"Simple Medicine," Feature Article, August 2004

simple medicine

A medical device maker streamlines a mechanical design.

by Harry Hutchinson, Executive Editor

The maker of three new clinical testing machines is touting them for their efficiency. The manufacturer, Abbott Laboratories' diagnostics division, claims that the systems improve laboratory workflow. It also designed the machines to be efficient to assemble.

Abbott Diagnostics, based in Abbott Park, Ill., markets equipment for immunoassays and other chemical
analyses. These are the tests that can find cancer and
cardiac markers, hormones, drug traces, and other signs in the blood of medical problems or questionable behavior.

Sold under the brand name Architect, the machines are the i2000sr and the c8000. Each is designed to perform a battery of tests. When they are combined, they make up a third product, a configuration called ci8200.

Although the machines can analyze various body fluids, most of the tests are of blood samples. Depending on the type of testing, the i2000sr can perform as many as 200 tests an hour, and the c8000 as many as 1,200.

A patented feature of the machines is an automated system called the retest sample handler, which can hold up to 135 sample vials for the i2000sr, 185 for the c8000, and 335 for the ci8200. The samples, which are accessible to a three-axis carrier transport robot, can be picked up in any sequence so they can be retrieved for retesting when it is necessary.

According to Bob Luoma, a systems engineer at Abbott Diagnostics' design and manufacturing site in Irving, Texas, designers worked early on with an eye toward keeping manufacture of the sample handler simple and the number of parts small.

"Obviously, parts that don't exist don't have to be bought, inspected, or shipped, and they never arrive late from the vendor," Luoma said. "Moreover, when individual part functions are consolidated into single multifunctional components, the potential tolerance and wear problems that can occur between part interfaces are eliminated and quality improves." Abbott makes 400 to 500 of the machines a year.

Designers say they were helped by Design for Manufacture and Assembly, or DFMA, software during the development of the system to reduce part count and assembly time of a number of key subsystems. The software is the product of Boothroyd Dewhurst Inc. in Wakefield, R.I.

The original tray platform in the sample handler had 86 parts and took 12 minutes to assemble. Designers eventually reduced the part count to 46 and assembly time to five minutes.

Abbott eliminated a number of parts by designing a
single-piece aluminum structural extrusion to function as the backbone of the sample handler. The extrusion includes two rails for carrier transport rollers and a linear bearing guide for the carrier positioner mechanism. Eliminating separate rails and associated fasteners, and reducing machining of large surfaces resulted in significant cost savings. In addition, the single extrusion offers improved structural strength in the given space at the lowest weight. Fewer parts minimized tolerance stackup.

A single extrusion combines the functions of many individual parts.

The top rail, which supports the covers of the sample handler, started with 19 pieces and ended up as one. In an early prototype, the top rail was a custom extrusion with separate hinges, each of which was fastened with two screws. Eventually, designers incorporated the hinges into the extrusion itself, eliminating parts and fasteners.

Electronic components in the original design included circuit boards and cable harnesses in different configurations for each module type. The harnesses were bulky and difficult to install. "It was like trying to pack the nosecone of a rocket," Luoma said.

The final design has 18-inch-long circuit boards that can be joined to form a continuous board up to 10 feet long, without cables.

The development team included representatives from engineering, service, and the factory floor, to combine practical and theoretical perspectives. For example, factory assemblers were invited to examine the product design for ease of assembly and service.

Luoma said, "When you're living every day with a
design, it's really hard to get a perspective on it, and a factory assembler has a different mindset from an engineer."

Simply reducing the part count wasn't the only consideration in design. The tray platform contains power-bearing components and flip-up doors. "We wanted to ensure that those were all serviceable after the platform was assembled into the module," Luoma said.