The Koko Smartrainer exercise machine, manufactured by Koko Fitness Inc. (Norwell, MA), includes an integrated computerized "personal trainer" that automatically customizes each workout to an individual's particular needs. Not surprisingly, given the level of technology involved, actually manufacturing such a system required overcoming a number of assembly challenges.

For example, early on in the design process, engineers realized they had to find a viable fastening method for installing a printed circuit board assembly that senses the location of a pin in the weight stack, thereby tracking how much a user should lift.

"We needed [fasteners] that would allow us to position, align and join the sensor-board assembly to a metal tray that houses the electronic system components," says Joe Gately, director of manufacturing at Koko Fitness. Ultimately, Koko Fitness elected to perform the job using PEM ReelFast SMT threaded surface mount spacers from PennEngineering (Danboro, PA).

According to Koko Fitness Senior Product Engineer, Jeff Pearson, the company tried a number of alternatives, including a screw-and-nut arrangement, which required a through-hole in the sensor boards. However, such options took up too much room, given that the electronics had to fit in a very tight space.

"The amount of hardware with a screw-and-nut assembly would have doubled if we [had] opted for a screw, spacer, washer and nut," Pearson says. The PEM spacers require only a mating screw, which means less hardware and easier assembly. The fasteners also needed to be small enough to accommodate various traces and wiring. Measuring just 0.065 inch, the PEM spacers met this requirement.

In the final design, Koko Fitness engineers chose to use a pair of carbon steel spacers with an electroplated bright tin finish on each 0.06-inch-thick sensor board. These spacers are installed by an outside electronics contract manufacturer at the same time and in the same manner as the boards' other surface mount components, prior to the automated solder reflow. Being a permanent part of each board, Koko Fitness production engineers and operators don't have to worry about any loose spacers or nuts falling out and damaging electronic components as the boards are being installed. The spacers also ensure correct alignment during final assembly.

PennEngineering supplies the fasteners in a tape-and-reel configuration, with each recyclable 13-inch reel carrying up to 1,500 components. Reels conform to EIA-481 for automated assembly. Having the fasteners installed during board fabrication reduces the risk of boards being damaged by operators installing them with off-line equipment. It also accelerates final assembly.

For more on threaded fasteners in electronics applications call 800-237-4736 or visit www.pemnet.com.