Electronic Design

What's all this Carpal-Tunnel Stuff, Anyhow?

About 20 years ago, I was working on manufacturing methods. I had designed a new VFC circuit with a new printed-circuit layout. Not only was it a good circuit with a very effective design, it used just a handful of parts and the layout was improved for easier, cheaper manufacturing. I turned it over to the manufacturing engineers, and was very surprised when they listed the estimated assembly time as longer than my previous, comparable circuits.

I confronted the manufacturing manager. Armed with my computations, I showed him that this circuit should definitely take LESS assembly time, as I was using their list of individual component assembly times. According to these rules, if installing a resistor flat on the board was supposed to take 15 seconds, but installing a resistor on end was supposed to take 20 seconds, and I only built in horizontal resistors in this layout instead of the older vertical resistors of previous layouts, then they had better have a good reason not to say the assembly time would be shorter.

I got a big runaround. They never did come up with any satisfactory or rational reason, and they kept insisting they could set any arbitrary number they wanted to. I concluded the whole mess was completely corrupt. I mean, several other engineers and I had designed circuits that were supposed to have a LOWER assembly cost, and after they got in production we were told they actually had a HIGHER assembly cost. So if we thought we had done our jobs in designing a new, cheaper, more competitive product - and if the manufacturing guys, without any factual basis, were able to say the part was MORE expensive to make - then we could not possibly do our jobs. They were using a warped yardstick, and we weren't permitted to question them. That was the year about 10 engineers left Philbrick, and I was one of them.

But I did get to work with a couple fairly smart manufacturing engineers. We discussed why one design was more expensive to build than another. In the Philbrick tradition, we didn't just install a 1/4-W carbon-composition resistor in the board, like all of the other manufacturers. The assembler had to scrunch the leads really tight, and put the resistor into two 0.030-in. holes spaced exactly 5/16-in. apart. Now, every rulebook I ever saw for installing a resistor that has a body 1/4-in. long allows 3/8-in. space minimum between the mounting holes - and preferably 7/16 or 1/2 in. for ease of assembly.

However, at Philbrick, we bent the leads good and hard, and stuffed the leads in, and we never had any significant problems. No reliability problems. It did take more care and assembly time, though. But we always thought it was well worth it - because we were able to pack in more transistors, more Rs and Cs, more diodes, and a more complex circuit, getting higher performance than any competitor that used conservative spacings on their layouts. We always laughed when we saw pc boards with as much as an eighth or a quarter of an inch between components! How absurd!

Then, after the assembler stuffed in the part, she had to bend the leads over, flat and tight, and cut off the leads with her little 4-1/4-in. diagonal nippers. This was to make sure the resistor did not fall out, and to provide a good place for the solder to flow and make a good joint between the lead and the foil. The engineer who was working with me said that some of the assemblers got really sore in their wrists and had to leave their jobs. Other assemblers never had any such problem. That was my first introduction to what we once called Repetitive Stress Syndrome, or Carpal Tunnel Syndrome. (The word "carpal " means pertaining to the wrist.) These women who had to make 500 or more snips per hour, without much of a break, were doing lots of work with their wrists, and when they weren't snipping, they were grasping those nippers, clutching them tight. Some of them got along with that work just fine - and some just could not take it.

Personally, I always enjoyed building things and installing the resistors and bending the leads exactly right, and snipping off the ends. I never got quite good enough to get up faster than the standard work rate - I was neither methodical nor consistent enough. If I had worked at it for 8 hours a day for a few months, I might have come up with some different opinions. But I had lots of fun, and I learned a lot. I convinced myself that I knew how to design printed-circuit layouts that could be manufactured small and quickly - even though the manufacturing manager insisted that I should shut up because I didn't know what I was talking about.

NOW, if you do certain motions with your hands and they really hurt, and then you get smart and stop doing it and your hands feel better - hey, no problem. BUT a lot of these women not only had real pain, debilitating pain in their wrists, they found that when they stopped, it did NOT get better for a LONG TIME!! THAT is not linear - that hurts!! So over the last 10 years, a lot of people have found out about Repetitive Stress problems.

Over the last 20 years, lots of people have been doing much more typing, data entry, and word processing. I certainly have been doing a lot more typing. My columns alone take about 50,000 words of typing per year, and my recreational typing almost that much, and my typing at work is comparable. This doesn't seem to bother me at all. But I've talked with people who find that they're doing so much typing that their wrists are going to ruin. They can't drive their car; they can't hold a pencil; they can't put on their clothes. They find that they have to stop and rehabilitate their wrists, and do a completely different type of work, with no typing, until their wrists are recovered. It's NOT a joke, even though it's hard for us sturdy types to comprehend.

Why do wrists get sore? Well, your wrist bones make a little slot or "tunnel " - the carpal tunnel - where your tendons and nerves pass through on the way to your hand. If these tendons go through a great deal of activity and start to swell up, there's no place for them to go, so they expand and start to crush the nerves. If this doesn't stop, these nerves can be badly damaged, and may recover very slowly.

So my first advice is, if you're doing a lot of typing or any other repetitive hand motion, and your wrists are getting sore, STOP IT REAL FAST. Because it ain't likely to get better, and it's likely to get worse. AND, worst of all, it will probably not get better very quickly when you stop. So, it's important to STOP and get good medical advice. Now, I'm not a doctor. But, from what I've read1, if you stop for a good while and let your wrists get better, and then take precautions, you may eventually be able to return to that type of work. For example, you may have to get a different type of ergonomically friendly keyboard. You may need a wrist-cushion to cut the strain on your arms. You may have to force yourself to take plenty of breaks, and cut down considerably on your total typing. But you will have a chance to recover - something you won't have if you just try to gut it out.

Let me cite a similar example - mountain sickness. When hikers from the western world go to the Himalayas, they go from a hiking experience of 10,000 or 12,000 feet, maximum, to up above 18,000 feet or higher. I mean, almost none of us has any experience at sleeping above 14,000 feet, but in Nepal or Kashmir or Tibet, any serious expedition goes way above that. As the expedition ascends, some people start feeling lousy and weak, with trouble breathing, etc. Many young hikers think they're so tough, they think they can just tough it out and climb higher the next day. Those are the ones that die. The ones who get good advice from their expedition leader, or their medical guys, and go down the mountain - they all recover. The chances of death or serious injury are negligible if you descend fairly promptly. Young bucks hate to do this - they hate to admit to any weakness. But you HAVE TO descend - there's no known medical treatment to "cure " mountain sickness. (Some expeditions bring along a "Gamow bag, " a sort of inflatable sleeping bag that can add some pressure and let a sick person get some of the effects of lower altitude without descending, but that's just a temporary deal.)

Likewise, if your wrists feel like they're being ripped up by repetitive stress, you must stop, or they will NOT get better. Stop, and consult with medical experts who know about this stuff. Avoid the possibility of permanent nerve damage. Years ago, when people didn't know any better, and even most doctors didn't know about it, ignorance was excusable. Not any more.

Who else does repetitive stuff? Musicians. Most concert musicians and symphony artists do a LOT of practice - sometimes more than is good for them. Some people can take it, while others get damaged. Pianists who use all their fingers and practice until perfection can have this problem. It's not a matter of not trying - it's a matter of trying too hard. Don't be ashamed of stopping. It's not anything that you have any choice about, and it's not a matter of willpower. I ran into one person who did a lot of typing, and I saw a splint on his wrist. When I inquired, he said that a little typing didn't bother him much, but he discovered that he slept at night with his wrist bent down as an unconscious habit. This wound up, when combined with a lot of typing, nearly wrecking his wrists. When he put on a short splint for typing, PLUS a long splint for sleeping, to prevent him from cocking his wrist hard for hours on end, the problem diminished to very manageable levels. Then, with an improved keyboard and rest pads for his wrists, he could do some typing. I know that I sometimes cock my wrist, a little bit one way or another, when sleeping. But it doesn't seem to have caused any problems - not yet anyway.

One time I discovered I was getting a real pain in my neck. I finally figured out why - I was assembling some special circuits at my kitchen table. I'm just near-sighted enough that I wanted to get my best view by bending my neck over to get a close-up look at this work. I decided to put my work on top of a stack of four big telephone books. The neck problem went away.

So just remember - pain is one way for your body to tell you that you ought to STOP what you're doing. Hey, I'm not a doctor, but I'm smart enough to warn you that in certain nonlinear cases, it's important to stop first, see a doctor, and ask questions before you resume your work - or else! For more information on Carpal Tunnel Syndrome, ask your company's medical advisor, or ask your doctor. Or buy the inexpensive brochure listed below.

All for now. / Comments invited! RAP / Robert A. Pease / Engineer

Address:
Mail Stop D2597A
National Semiconductor
P.O. Box 58090
Santa Clara, CA 95052-8090

Hide comments

Comments

  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Publish