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Machine Vision-Based Video Gauging
by Nello Zuech, Contributing Editor - AIA Posted 07/11/2006
While my introduction to what we now call ‘‘machine vision’‘ was back in 1969, the initial applications of the then primitive technology were in government R&D labs or government funded university labs. It was not until 1978 that I became involved in what we now call machine vision. The company I was with was not really in the imaging business. Their principal business was in electro-optic devices. However, the Engineering Manager at the time had this passion for computer-based television and so he essentially bootlegged the development of the first computer-based video-based gauging system targeted at offline dimensional measurements of parts that fit into a 6’‘ measurement envelope.
Market research was also bootlegged to assess the specifications for such an instrument that would appeal to a reasonably large percentage of the formed product markets. The challenge, however, was to actually design and build a system that would satisfy the specification when developed given the state-of-the-art components required by such a system: analog vidicon cameras, optics, X-Y tables, not to mention the computer technology available at the time. Compounding the development work was the regrettable decision that the translation stage could be designed and built internally. Significantly, the company did not have a single mechanical engineer on the staff.
The combination of drift experienced with the analog vidicon camera, magnification errors associated with the optics (telecentric optics were a dream at the time – much too expensive to even consider), and translation stage errors, while at the same time the parent company finding out about the bootlegged project and recognizing it as a dilution of limited engineering resources that could be better directed toward enhancing the traditional product line, ultimately doomed the product.
Nevertheless, as the product was widely promoted at Quality trade shows and physically transported in a van throughout the country for local demonstrations, the seed was planted for the concept and it was not long after that companies produced versions that did meet the original specifications. Today with the advances in the underlying technology (solid-state megapixel cameras, telecentric optics, precision stages, lighting as well as computers) machine vision-based video gauging systems can be found throughout manufacturing industries engaged in forming products based on one process or another.
Today one finds a range of such products both in terms of measurement envelope, features and capabilities. Versions include totally interactive systems where an operator physically positions cursors between points to be measured (the system actually performs edge enhancements and often sub-pixel processing), systems that have part-specific programmable X-Y translation stages to those that are completely part-specific programmable and do not require any operator intervention at all to make the measurements on the part. With megapixel cameras there are versions that perform full field-of-view measurements and do not have a translation stage. Versions also come with different lighting arrangements that can optimize the lighting required for the specific part geometry. Versions also come with various 3D measurement capabilities, both contact and non-contact.
Needless to say the price range is proportional to the features of the system – from under $10K to upwards of $200K.
With all this in mind we solicited input for this article from all known sources of machine vision-based video gauging systems. Two companies elected to participate. However, it is noted that one of the responders actually represents four companies that are now under one umbrella, so to speak, after a series of acquisitions.
- Richard B. Amon, President, Optek
- Fred Mason, Marketing Communications Manager, Quality Vision International
1. How would you describe your product line?
[Richard B. Amon – Optek] Our company designs and manufactures a comprehensive line of video-based (VideoMic) and x-ray based (InnerVision) coordinate measuring machines.
[Fred Mason – Quality Vision International] We have four companies that market video measuring systems. I am with the parent company, which does not market its own brand.
OGP (Optical Gaging Products) - We offer 3 lines of SmartScope® systems, with models ranging from bench-top to large travel floor models in each line. Most OGP systems are available with other sensors (multisensor) to get more measurements from a single setup (than is possible using video alone).
RAM Optical offers a range of products from simple vision inspection systems up to CNC measuring systems.
VIEW Engineering offers 3 lines of systems aimed at process control and electronics applications.
Micro-Metric offers a range of systems based on microscopic imaging - some general-purpose, some application-specific.
2. What specifically differentiates the models you offer?
[Fred] OGP SmartScope systems are known for their ease of use for any application. The multisensor versions are known for the tight integration of the sensors into the metrology software, and for user-friendly features such as sensor deployment and retraction under program control. These general-purpose machines support a wide range of applications in a wide range of industries around the world.
RAM Optical systems are known for their simplicity. The ‘‘inspection made simple’‘ theme applies to all RAM systems. RAM brings video inspection and measuring to users who want to do the job and go on to the next thing.
VIEW Engineering systems are known for unique features and capabilities like dual magnification optics that provide instantaneous mag change, and high-speed linear motor drives. VIEW Pinnacle systems combine high-accuracy and high-speed stages.
Micro-Metric systems use turret-mounted microscope optics in its range from manual bench-top machines to the 1.5 meter travel VPM for measuring Gen 6 & 7 LCD photomasks.
[Richard] Our systems are predominantly ‘large format’ machines, the smallest of which has a measuring envelope of 28’‘ X 24’‘.
3. Would you characterize machine vision-based offline video gauging systems as ‘‘hardware-centric’‘ or ‘‘software-centric’‘ and why?
[Richard] Neither. The systems are co-dependant on hardware and software. Today’s machines must be made physically repeatable in order to benefit from the mapping and correction capabilities of the software.
[Fred] Both. Although it is easy to generalize that all systems have optics, camera, stages, scales, lighting...the quality and capabilities of any of those items can vary dramatically. In addition, the ultimate capability of a measuring system is determined by its software. The best hardware components operated by weak, limited software is not a good value. Nor is heavy-featured software with mediocre components. This issue is even more critical when additional sensors are brought into play.
4. What are the critical parameters of a machine vision-based offline video gauging system that a prospective customer should understand?
[Fred] See previous. In addition the total cost of ownership must be understood. The initial system price is just one factor. The quality of components and fit and finish come into play over time. Long term stability, serviceability, and reliability must be taken into account. An unreliable measuring system used for critical measurements is not a very good value, but important process and business decisions can be made with an accurate, well-designed video system.
[Richard] From my experience, the least understood parameter affecting machine performance (accuracy) is the machine’s environment. Prospective customers should consider their accuracy requirements carefully before positioning a machine in a measurement-hostile environment.
5. What are the skills required to program and operate a machine vision-based offline video gauging system?
[Richard] Our systems utilize one of the ‘industry-standard’ software packages – QC-5000 – from Metronics. This Windows® based program is easily taught to individuals who have a basic understanding of metrology – and the Windows operating system.
[Fred] Speaking only of programmable systems, this is an area where it is important to understand where and how a system will be used. Unless there is one person who will program and operate the machine, many companies instead have a programmer and several operators. Programmers must understand how to use the system tools to get the best results from every situation, so the part routines function properly when used by others. Programs can be written so all the operator needs to know is how to load parts and start the routine. This allows video measurement in a work cell where a machine tool operator can load parts he/she makes into a video measuring machine, start a routine, and go back to making parts. And with programming tools it is easy to copy and edit a part routine to deal with part specification changes and other production variations.
6. How do you support your products - training, documentation, warranty, post installation service, software revisions? Are these free or is there a fee?
[Fred] This can vary by company, but in general training is provided at system installation. Hardware and software documentation is either online or hardcopy, or both. All systems have a standard warranty. Extended warranties and service contracts are available. The software revision policy depends on the extent of the revision and the version/age of the system involved.
[Richard] Our company provides training either directly or through factory-trained representatives. All documentation – including part views, exploded views, BOM’s, wiring diagrams, and schematics are accomplished in 3D-CAD with each machine stored on CD in its particular configuration. Periodic software upgrades are provided free-of-charge.
7. Where do you see breakthroughs coming in the specific infrastructure technologies (hardware and software) that are the basis of machine vision-based offline video gauging systems that will result in further improvements in the near future - next three years?
[Richard] Line-scan cameras, megapixel cameras, laser probes, flat panel x-ray detectors and software enhancements will be the primary enablers for machine enhancements over the next several years.
[Fred] Although multisensor video measuring machines first appeared 20 years ago, they are now becoming more prevalent and widely used. The benefit of doing more measurements in a single setup is consistent with the push for improved productivity. Rather than measure one part on three different machines, each with its own fixture, unique software, associated training issues, and service requirements, a multisensor video measuring machine can use three (or more) sensors in one setup, all operating automatically while the operator is doing something else to add value to the organization. The range of sensors being integrated is expanding. On the software side, continued tightening of integration with CAD drawings is making programming easier and measurement data more meaningful. Fitting software is taking video measurement results and doing more with them to take analysis up another notch.
Another new technology is offered by VIEW Engineering. Unlike traditional video measurement where the part or optics moves from site to site, stopping for each measurement, flowing video is a technique where images are captured without stopping the stage. Images are processed at the same time improving total throughput 3-5 times.
8. What specific performance improvements are anticipated driven by these forthcoming technological changes? How will they impact the use of these systems?
[Fred] The performance improvements are in overall productivity of the organization using the measurement system. High volume, low mix manufacturers can get high throughput, consistent with production rates. High mix, low volume manufacturers can easily change part programs to get required measurements without delaying switchover production rates. Consistent, accurate performance of the measuring systems means manufacturers can concentrate on designing parts and processes that make them competitive. The continuous image capture capability allows more measurements per unit of time (3-5 times faster).
[Richard] Today’s products demand more precise measurements because of their increased complexity. This is especially true in the Printed Circuit Board industry – a focus of our engineering efforts. The measured features, while decreasing in size, are also increasing in number with 20,000 holes on a PC Board commonplace. Multilayer PC boards are also becoming more complex with customers designing boards with as many as 80 layers and measuring 50’‘ X 36’‘. Our InnerVision x-ray systems are designed to optimize the alignment of these layers so that their interconnection is possible.
9. What are the main markets for these systems and are there market changes within those markets that are driving the adoption of machine vision-based offline video gauging systems?
[Richard] While our company focuses on the electronics industry, there are many others that will benefit from machine improvement. Sheet metal, plastics, glass, and other laminates are being machined for a variety of precision applications that are ideally suited for use with our OPTEK machines.
[Fred] The QVI companies do not build market-specific systems. Any manufacturer with parts that have dimensions that fit into our range of capabilities is a candidate. The speed of video measuring systems and their ability to measure many points at once is making them attractive to companies that have relied on single point measurement such as CMMs. In addition, tighter tolerances are forcing manufacturers to abandon hand gages for the accuracy and repeatability of video measurement.
10. What impact do these changes have on the inspection requirements for machine vision-based offline video gauging systems? And how will machine vision systems have to change to address these more demanding requirements?
[Fred] The machines will continue to change as available technologies develop and application requirements change. For example, the need for larger travel machines is being partially driven by the increasing size of LCD TVs. On the other hand, smaller critical features of MEMS require measurements at higher magnifications.
[Richard] Speed, accuracy, price, and dependability are critical parameters that will all have to be addressed in the increasingly competitive international marketplace.
11. As a supplier of machine vision-based offline video gauging systems what are some challenges you face in marketing machine vision systems?
[Richard] One of the biggest problems in marketing our systems internationally is the extremely high cost of shipment – by air or sea. By nature these machines are not only large – but being granite based - quite heavy. Duties and other import/export fees as well as restrictive crating issues are also costly. Another problem is ‘specmanship’ – where competing companies make speed and accuracy claims that cannot be supported. Purchasing agents become involved in the sale and frequently go for the ‘lowest bidder’.
[Fred] A marketing challenge is helping our customers understand about all the things to consider when choosing a particular system.
12. What advice would you give to a company investigating the purchase of a machine vision-based offline video gauging system?
[Fred] Make an informed decision. The best test is to get data from the machine using your parts. Even then, be sure to consider the longer-term issues of system reliability, quality of construction, and durability. Also consider the manufacturer - do they have a track record? Are they committed to the technology? Do they engineer systems or simply assemble parts? Will they be there for you next year and five years from now?
[Richard] My personal advice to companies considering the purchase of a machine is to actually run their products on the machine they are considering. Further – they should, if possible, visit the company that produces the equipment and accomplish accuracy and repeatability tests. A purchase of this magnitude – in some cases exceeding US$100,000 - warrants the establishment of a relationship as this machine could easily be in use for decades.
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