Motors

Ultraminiature Brushless Dc Motor Available for Medical Applications

Will enable further miniaturization of devices

RMB MINIATURE BEARINGS INC. (Mountain View, CA), a manufacturer of precision miniature bearings, has developed an ultraminiature brushless dc motor. Being dubbed as the world's smallest commercially available motor, the Smoovy comes in diameters of 3 and 5 mm.

With this small size, design engineers will be able to miniaturize existing devices and create new ones that were previously unattainable. Possible medical applications include endoscopic camera positioning systems, microdrives used in minimally invasive surgical instruments, pump drives for microdosage systems in implantable and external dosage pumps, and pump drives for micro analyzing systems.

Low inertia makes the Smoovy motor capable of quick changes in speed and direction as well as rapid start/stop cycles. It can be configured as a stepper motor, a high-speed motor with variable speeds ranging up to >110,000 rpm, or as a powerful switch. Short-term bursts of high torque are possible with high voltages and current.

The efficient brushless dc construction provides powerful initial torque and a mechanical time constant of 130 milliseconds. According to RMB, the motor offers distinct advantages over motors with brushes, such as lower friction, better starting when heavily loaded, higher power density, improved efficiency, longer life span, the use of fewer mechanical parts, and cleaner operation since there are no brushes to wear out.

Constructed of high-quality parts built to tolerances of ±1 µm, the motor is available with ball, ruby, or sleeve bearings. The ball bearing design includes 17 balls measuring 0.2 mm diam with roundness tolerances to within 0.0002 mm. High-precision, standard, and economy versions can be selected depending on the user's speed, load, and life-span requirements. RMB can also custom design motors using its proprietary software.

The Smoovy motor operates in a range of 2 to 9 V dc rated at a current range of 20 to 200 mA. Power can be supplied by batteries connected to a three-phase controller. At optimal operating speeds, the temperature of the motor decreases, providing benefits for applications requiring sustained high speeds. A motor rotating at speeds up to 5000 rpm can also be reversed by switching the direction of the rotating stator field. This functionality makes the Smoovy suitable for direction-switching micro applications.

Precision planetary gearheads are being developed for both the 3- and 5-mm versions and will be made available by mid-1997.

Plastics

Medical-Grade Polypropylene Resins Withstand Repeated Gamma Radiation

Resins will not degrade, deteriorate, or discolor

GAMMA-10 PLASTICS, INC. (Minneapolis) has formulated a line of medical-grade polypropylene resins that can withstand repeated, high doses of gamma radiation, as well as other methods of sterilization such as EtO and autoclaving. According to the manufacturer, the various grades of Gamma-Resin can be radiation processed with virtually no degradation, deterioration, or discoloration. The materials can be sonic welded, heat welded, or heat sealed.

Both extrusion and injection molding grades are available, as well as two film grades that have been engineered to provide unidirectional linear-tear capability for such applications as pouches, bags, drapes, and tapes. Two resins are particularly well suited for syringe manufacturers that want to switch to gamma or E-beam sterilization methods.

Motion Control

Linear-Motion Guides Eliminate Ball-to-Ball Friction

Reduce noise levels by up to 50%

LINEAR-MOTION GUIDES equipped with specially designed nylon raceways that eliminate ball-to-ball friction have been developed by THK America Inc. (Schaumburg, IL). The SSR-series linear-motion guides eliminate friction between adjacent balls by cushioning them with a lubricating oil film. The absence of metal-to-metal contact results in a 5-db reduction in noise emissions, a 50% improvement over the company's previous line. In addition, the retainer has been designed with a wide contact area between the balls and the oil pockets, allowing for smooth, high-speed ball rotation with less heat generation and longer maintenance-free operation than traditional technologies. The balls are uniformly lined and circulated, producing smooth movement with 1/10 of the torque variation of conventional systems.

Since the reduction in noise emissions is a critical issue in hospital environments, the guides have numerous potential applications within the medical device sector. Medical scanners are but one example of the type of hospital equipment where silent operation is an important factor. In addition to medical equipment, SSR LM guides are well suited for cleanrooms and any other environment where low friction, long life, and low noise emissions are desired.

The guides come in rail widths of 15, 20, and 23 mm and are supplied with standard blocks measuring 34, 42, and 48 mm in overall width and 57, 66.5, and 83 mm in overall length (excluding the lubricating nipples). Dynamic load-carrying capacities are 9.51, 12.5, and 20.3 kN; in static mode, the capacities are 16.5, 23.4, and 36.4 kN. Five accuracy standards are available, ranging from normal to ultraprecision.