#Arm50: The origins of the portable measuring arm

Today’s portable measuring arm class of measurement devices has its beginnings in 1973, when the original Vector 1 tube measuring arm was developed Homer Eaton, of the Eaton Leonard corporation

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Where did the portable measuring arm come from?

The Absolute Arm range – Hexagon’s portable measuring arm portfolio – has its origins with the creation of the Vector 1, a measuring arm developed specifically for tube measurement applications. Its originator was Homer Eaton, who founded the Eaton Leonard corporation in May 1973 to bring his creation to market.

Eaton had always had a fascination with tubes, going back to his high school days when he bent exhaust tubes for hot rods in his garage. Following the company’s first sale in October 1974, the original patent for the Vector 1 was filed on April 18, 1974, and was eventually granted patent number 3,944,798.

A little over a decade later Eaton partnered with Romaine Granger to co-found ROMER, which later became part of Hexagon. In 1986, ROMER introduced the first ‘portable’ measuring arm to the market, the System 6, and the device class has only grown from there, leading to the modern eight-generation 3D-scanning-capable Absolute Arm currently offered by Hexagon.

There’s no doubting the debt the current Absolute Arm – and every other portable arm on the market – owes to Eaton’s original Vector 1.

What were those first measuring arms like?

That first incarnation of measuring arm was bench mounted and used a computer the size of a compact refrigerator to power it’s by modern standards primitive software, which was also developed by Eaton. The device would capture the bend geometry of a bent tube such as an exhaust pipe, using a set of electrical contacts inside its V-shaped head.

This legacy can be clearly seen in the modern Absolute Arm generation, which still supports tube geometry calculation using a specialised infrared tube probe operated through Hexagon’s dedicated tube and wire inspection software platform BendingStudio XT.

It wasn't until later that the arm was re-imagined as a device to capture the geometry of all kinds of other objects – not just tubes – and advances in computing technology made the devices at first ‘luggable’, and then – with the advent of the laptop computer – truly ‘portable’.

That was the objective when Eaton and Granger founded ROMER: to introduce a portable articulated arm into the metrology marketplace. The timing was nearly perfect with the advent of the personal computer, while the 3D measurement needs of the aerospace and automotive industries were simultaneously rapidly emerging to create demand for such a product: the ROMER System 6 was born.

Talking with the grandfather of the measuring arm

Homer Eaton has been an inventor and entrpreneur his entire life, and was involved with the research and development of measurement and inspection hardware, electronics and software throughout his career.

Several years ago, Hexagon’s Bill Fetter interviewed Eaton to hear in his own words how he experienced those early days of what we now call portable metrology.

FETTER: What problem were you trying to solve when you conceived the Vector 1?

EATON: I was trying to measure the geometric path of a bent tube shape, rather than the difficult convention of measuring the component features of lengths and angles.

FETTER: What level of precision where you looking to achieve at the time?

EATON: I was looking to achieve an accuracy of 1/32" [0.8 millimetres].

FETTER: Did you envision the product as a solution for mainstream metrology applications?

EATON: No, I did not at the time.

FETTER: Were there any huge ‘A-ha!’ moments in the history of the product that you remember in particular? If so, what were the circumstances surrounding them?

EATON: Yes, there were. The first was simultaneously measuring a point and a vector, and this was the origin of the ‘Vector 1’, the articulating arm for measuring bent tube shapes. The second moment was the infinite rotation, where we digitised raw encoder signals and transmitted digital data through slip rings. And lastly was the GridLok concept of the arm inside a virtually unlimited measuring envelope, allowing leapfrogging without error stack up. The beauty is that this was accomplished with virtually no hardware – it's just a mathematical feat involving triangles.

FETTER: At what point did you decide to make the jump from inspection of tubes to other components?

EATON: In 1974, George Goodreau, plant manager at Westinghouse, inspired me to build units for measuring steam turbine blades on the shop floor. We built a number of roll-around arms for this purpose.

FETTER: When did you realise this technology could be a truly portable device?

EATON: In the late eighties, Romain Granger convinced me that we could build an even lighter unit and fold it into a more compact shape by adding one more axis. It was about this same time Toshiba introduced the portable computer.

FETTER: What were the main initial impediments to portability?

EATON: There were three distinct roadblocks:

Having a portable computer – the Vector 1 minicomputer weighed 40 pounds [18.1 kilograms].
Being outcasts from the ‘CMM’ world in a world of granite, walls and arrogance.
Needing a rigid support base for the arm.

FETTER: What do you consider to be the most interesting application for the arm that you've seen?

EATON: Measuring a Steinway piano and letting metrology merge into the world of art.

FETTER: Which do you prefer to invent: hardware or software?

EATON: Hardware. It is more tangible, challenging and creative.

FETTER: Your volumes of notebooks of ideas are somewhat legendary at ROMER. How many things in those notebooks do you suppose actually turned into products or product enhancements?

EATON: My notebook ideas turned into hardware, electronics, software – well over 50 products in the long run.

FETTER: Where do you draw your inspiration from?

EATON: Stress, the mother of innovation!

FETTER: What were the most difficult design challenges throughout the history of the arm products?

EATON: The main challenges were the twisting of the wires at the arm joints, and the elimination of the mechanical coupling between the encoder and the arm axis.

FETTER: Thinking back over the entire history of these products, what feature or product are you the most proud of?

EATON: Definitely arm calibration. Creating the mathematical algorithms and artefact techniques for calibrating the arm was the fundamental basis for our success.