Ten in the bed: ten motors drive medical imager's print mechanism. (Application Ideas).

The Horizon Multi-Media Dry Imager from Codonics, Middleburg Heights, OH, is capable of developing printed images and reports for MRI, CT, ultrasound, fluoroscopy, oncology, PACS and nuclear medicine units. It handles three, easy-to-load, sealed, disposable media cassettes at once, allowing the Horizon to switch from color to grayscale without manual intervention. (The Horizon is said to be the first imager on the market capable of this feat.) This diagnostic imager creates dry images on film and paper. Grayscale images are direct thermal, while the color images use dye sublimation technology.

Print speed is considered an essential asset. But in order to fulfill this time-sensitive operation, all components must work in unison. The image must be received and processed; the mechanism in turn must actually produce a copy from this operation. The components carry media through the imager, bring printing components into contact with the media, or drive components into positions from which they can drive the media. Often several of these operations are working simultaneously and must be coordinated with speed and accuracy. Since not everything moves at once, the actual rate of motion is very important. According to Kevin Roach, mechanical engineer for the Horizon product, "The faster our mechanisms can get into position, and the faster they can physically move the media through the system, the better off we are. We needed motors with a higher power output, allowing us to move everything faster, but with the same load capacities. The result is faster print times with the same image quality and reliabilit y."

By the time the motor decision was made, almost all the gear and part placements had been selected. Documentation provided all the necessary technical information to allow the company to predict which motor! gearbox combinations would be best suited to each of the applications within the imager. For the purposes of making the equipment rugged enough to handle repeated use, the company elected to use metal gearboxes. "The gearboxes were available with planetary geartrains, which also made for a more rugged product," Kevin adds.

Codonics performed extensive testing of the motors and their mechanisms. "A lifetime's worth of testing for specific mechanisms that have a hard stop, and a lifetime's worth of normal operations," Kevin said. "Using encoders allowed engineers to always know how fast the motor rotated, so that they could squeeze all the speed possible Out of the system," according to Kevin.

Seven 22 mm and three 16 mm DC motors from Maxon Precision Motors, Burlingame, CA, are used in the imager. A variety of gearbox ratios are used in conjunction with Maxon-supplied rotary encoders, which are installed on all but two of the motors. The encoders provide the home and feedback signals necessary for the hardware/software controls to pick, feed, print, and select a receive tray. In order to understand the motor applications within the unit, it's best to know a little more about the imager operation. There are ...