Author: Jaycen

I have worked in the roll forming industry since January 11, 1999. I started out at the premier machine controls company for the industry at that time, and have since gone to work on the end-user side of manufacturing. My expertise is in general roll forming principles, length control, punching, servo systems, flying die, feed-to-stop, boosts, Lean Six Sigma, and Computer Integrated Manufacturing. I have installed, retrofitted, moved, or started up hundreds of roll forming lines in dozens of companies on four continents. For a number of years I was a presenter for the Fabricators & Manufacturer's Association at their annual World Class Roll Forming event, as well as at annual trade shows.

Press Consistency

Unless you’re using a servo, press consistency is crucial to length accuracy in flying punch and cut applications.  Without servo positioning, timing variances in the press will directly relate to length tolerance error, and the faster you run the line, the worse even small timing variances will affect length.

For instance, if you’re running a roll former at 400 fpm, that’s 80 ips.  At that speed a timing variance as small as ±0.003 s will cause a total length variance of ±0.24″!

Even the best 24 VDC relays have a switching time of ± 0.003 s.  Thus, running a press fire output through an electro-mechanical relay could easily induce a total length variance of almost 0.5″.  That assumes you have no encoder tracking issues.

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We Don’t Know What Our Margins Are – How Do We Take Decisions?

During my time in the Roll Forming Industry, I have been in dozens of companies across the United States and around the world.  Frequently, I have found myself in conference rooms with C-level groups trying to implement a new ERP system.  Since I worked for a company that made MRP scheduling software for manufacturers, we were a critical vendor and typically brought in early in the process to consult.

In these meetings, I have heard the same conversation over-and-over.  The first time I heard it, I was shocked, but since then I realize most companies must operate the same way.  It usually comes from someone in Accounting, and it goes something like this, “We don’t even look at the paperwork that comes off the floor anymore.  It’s usually meaningless.  Every time we’ve tried to reconcile what the Operators write down with what we measure coming off the line, it’s either wildly inaccurate, or there’s so much error it doesn’t matter.  We know what we spent last month to purchase things.  We know what we shipped out.  The rest must be waste.  We just have no idea where all the waste is coming from.”

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Encoder Measuring Wheels

Throughout my career, people have asked which type of measuring wheel is the best for use with a rotary encoder. The short answer is, whichever one gives you the best result on your specific application. Obviously, the real answer is a bit more complicated.

There are four main types of encoder wheel:

  • Rubber or Rubber-coated
  • Magnetic
  • Phenolic
  • Knurled Steel or Aluminum
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Quadrature allows a length control system to count four counts for one pulse from a bi-directional (two-channel) encoder.

A two-channel encoder is capable of reporting direction as well as movement.  Typically, there is an A channel and a B channel.  As the shaft of the encoder turns, pulses from both channels are being sent to the length control system.  The two channels are always offset by 90 degrees, so one channel will always lead the other channel depending on direction.

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Encoder Basics

Since the majority of roll forming lines use a computer to control punch and shear operations, the majority are also using rotary encoders to measure length.  If the computer control system is the brain of the machine, then the encoder is the eyes and ears of the brain.  Everything the length control system knows about the material – distance, speed, direction of movement – comes from the encoder and the measuring wheel affixed to its shaft.  It is for this reason that nearly all length variance problems are due to the encoder, the measuring wheel, and how they are tracking the material.  The computer that controls the machine and its parameters are almost never the cause of length variance.  Variance usually comes from the real world.

To understand how the encoder plays such a vital role in controlling length, it’s critical to understand how an encoder works.  You must also understand some fundamentals about the geometry of the measuring wheel and how alignment and mechanical backlash (slop) affect consistency.  This post will cover the fundamentals of encoder function.

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Length Control

There are three primary methods of controlling length on a roll former – gauge bars, positive stop, and encoders.  The first two methods are completely mechanical, with the last being electro-mechanical.

Length Control Methods

  • Mechanical
    • Length Gauge Bar
    • Positive Stop
  • Electro-mechanical
    • Encoder

Length Gauge Bars and Positive Stops

Gauge bars and positive stops have been around since the start of flying die applications.  They are probably the oldest method of length control for roll forming applications, but they’re still in use today.  That’s because they typically offer the best accuracy and consistency for the lowest cost.

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I’m Back!

After a long absence, the website is back.  I’ve changed jobs a couple of times in the last few years, and my hosting company sold out to another company.  It took months for them to move everything over to the new company, and in the end they lost my database.  Shame on me for not keeping an up-to-date backup.  Yet, here we are.

Most of what was on the site was a version of a whitepage I’d written for some function or another, so it won’t take long to recover most of the material.  In reality, most of my traffic is from people looking for the correct methods to calculate things like encoder resolution, but I’m glad to provide a useful service, no matter how small.

If you’re in the industry, have an interest in things “roll forming”, and are looking to learn a few things about the process then bookmark the page and check back from time-to-time.