While I worked for Panasonic Factory Automation, I installed several MVIIc chip shooters. These machines placed about 10 surface mount chips per second. If the placement rate dropped below about 99.99 percent, it was time to stop and fix the problem. I had installed and verified the calibration of a machine in a new manufacturing area at Celestica, then a subsidiary of IBM. During the acceptance testing, the chips were slightly skewed, but within specifications. The machine didn’t fail, but it wasn’t as good as we expected it to be.
The calibration involved the theta 1, 2, and 3 axes. The procedure was to install the large camera jig to a head on the turret, manually index it to the theta 1, and engage the axis. Then we would carefully index the turret backward to the placement position and use the X-Y table and a dial indicator to measure the runout. To do theta 2 and 3, the turret was indexed backward to the axis, engaged, indexed forward, and measured. All three theta axes were less than the specified runout spread. I think it was 0.1mm across 1 inch, but the chips were still skewed.
I checked and rechecked the theta axes calibration. A senior technician also checked the calibration and found nothing wrong. The manufacturing area was not in production yet, so the problem was not urgent. The fall-back position was that the chips skewing were still within specifications, so we could get along with the skew, but it wasn’t ideal.
The problem bothered me. I continued to wonder why the calibration was good while the placement was skewed. Eventually, I reviewed the placement sequence of operations step-by-step in my mind. The theta 1 engages the nozzle and rotates it to the pickup orientation. The machine indexes to pick up, picks a chip, and then indexes to theta 2, machine vision. Then it takes a picture of the chip on the nozzle. The machine then indexes to theta 3 and corrects angle variations detected at theta 2. The chip is then placed.
The machine then selects the nozzle for the next chip placement and indexes to theta 1. The nozzle brake at theta 1 contacts the nozzle to create drag to ensure engagement. But what was the theta 1 brake actually doing? The exact indexing angle of the theta 1 nozzle brake engagement and disengagement was not in the technical manual. I carefully indexed the turret manually a little at a time, walking from the front to the back, and observing the theta 1 nozzle brake. Lo and behold, the brake was contacting the nozzle during the turret indexing. I adjusted the theta 1 brake to clear the nozzle during indexing, and the skewing went away.
This entry was submitted by Glenn Aitchison and edited by Rob Spiegel.
Glenn Aitchison’s first field service job was in 1987. Since then, he has worked with automotive robotics and other industrial automation and machinery. He has received his Certificates of Qualification as an industrial electrician and as an industrial mechanic (Millwright).
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
This post is a good example of getting things just right. Even though the production was working OK, Glenn decided things weren't entirely right and he did something about it.
This seems a classic example of the value of having experienced people take a look at operations once in a while. A person who knows the process will have built up a "feel" for how things should run, and will often be able to spot when something isn't quite right -0 even when it is "within spec". Following up on such observations often discovers a problem that will eventually become a bigger problem. Nipping it in the bud prevents later losses that may include production loss due to work stoppages, equipment damage, etc. etc.
Alas, modern "lean" production systems are trying hard to eliminate those experienced people, who are perceived as too expensive, or discourage them from "gilding the lily" by trying to fine tune a process that is already within spec.
These trade-offs are subtle, but over time they make the difference between a "good" company and a "cheap" company.
And this principle applies not only to manufacturing, but to all sorts of other endeavors. My own field is embedded software engineering, where I increasingly see schlock completely clogging up the systems.
In the last couple of weeks, I have been immersed in a reference design package for a new microprocessor that my company will be adopting. Even though it comes from a large semiconductor house with a good reputation, it is full of stuff that looks like it was never reviewed. Many corners of the design have timing that is out of spec. The memory map is contorted. Elements of the software kit came from 3 different sources that were never reconciled, so the same registers are defined 3 different ways in different include files etc etc. It scares me to think that this stuff will end up in safety critical systems in many industries.
You're right about losing those experienced engineers. A lot of them were cut during the 2008 through 2009 recession. I understand that many of the experienced plant engineers are baby boomers who have retired over the past few years. I remember in 2007, there was concern in the automation industry that there were not a sufficient number of experienced engineers, but the recession took that pressure off.
Talk about getting things just right: It's instructive to note that placement of the surface mount chips was within 0.1 mm across one inch. Since a millimeter is 1/25th of an inch, it means that these chips were being placed with 1/250th of an inch...and this was unsatisfactory.
That was a while ago, but I think the brake pad was a rubber piece on a pivoting arm. The brake does not hold the rotational orientation of the nozzle - inherent friction in the assembly does that. The brake holds the nozzle still from spinning until the theta 1 meshes. There is very little friction wear in the braking action. The theta engagement is a steel V-block that nests into a matching V-slot in the steel nozzle. The wear that does happen is the V-shape of the block, from the vertical engagement about 10 times per second.
The loss of experienced engineers is most tragic indeed. My boss says (thinks) we can get replacements easily. I have seen examples of these replacements firsthand and have yet to be impressed. One can hire poor engineers and technicians for ten cents a pound, and they are overpriced. Great ones are cheap at one hundred dollars an ounce, but are difficult to find.
In my experience engineers and techies are one of two flavors. The first are hourly employees who think only of the paycheck and watch the clock. Most belong to a union but I have no problem with that. The second are the guys who think only of the problem(s) at hand and are somewhat mystified that somebody keeps putting money in their checking account. In the late 60's accountants in the company I worked for kept calling me because I seldom cashed my paychecks. Direct deposit later fixed this problem. Last Sunday I received a PDF manual on some equipment we were having problems with. This vendor went into work to find, and send me, the documentation. He is one of the second flavors.
Parado was exactly correct with the 20-80 rule where 20 percent of the people perform 80 percent of the work. In the long run the 20 percent earn much more money but usually find little time to spend it. Of that original 20 percent, twenty percent of them are the true Golden Child ones.
Good observation, Chuck. That shows just how precise it needs to be in order for it to be "right." So you have to hand it to this Sherlock Ohms to correct a situation that was so very close and "within spec."
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
4 
