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Design News, May 2013

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A typical DC iron core motor has a wound rotor, which is basically just a mass of iron. The coreless design means there is no iron core to the center. Using magnets, the tube and a custom winding eliminates the large iron core, saving weight from the system standpoint. Because of the type of construction, the motors can be much smaller in diameter, down to eight millimeters. For a portable lab analyzer, for example, being able to reduce the size provides more portability. For an infusion pump that a patient will wear on their hip, the goal is for the unit to be as small as possible. Using an 8-mm-diameter motor and associated Customizations of slotted DC motors for medical device applications include hollow shaft designs, which put the motor directly inline versus offsetting it with gearing to reduce 8-mm gearbox provides a very comsize, weight, and cost of materials. pact, yet powerful package. New designs are also achieving indevices. By drawing less current and putting less stress on that creased flexibility because neodymium magnets that increase battery, that is definitely a benefit. power density are becoming more widely used. And even in "Higher motor efficiency ripples through the entire design the smaller sizes, the design is not sacrificing the output of the of portable devices," said Dave Beckstoffer, project manager motor itself. for Portescap. "But more than anything, it offers increased "When you look at the difference between a coreless and an flexibility for the design engineer. The motor is not the only iron core motor, you don't have the iron losses as the motor is device in the system that is drawing power. If before the appli- rotating," said Beckstoffer. "With an iron core motor, there are cation had x amount of power from a 9V battery, for example, significant losses which translate into a lack of efficiency. The then suddenly if the motor rather than using one volt of that power put in is not achieving equivalent power out of the monow is using half of a volt, additional features and functionaltor. With coreless technology, these losses are practically elimiity can be added into the system using that additional power nated, which increases the efficiency of the motor's operation." that has opened itself up." In terms of a portable medical device running on a battery, Other applications for slotless motors include infusionbattery life is critical. The efficiency increase by coreless motype diabetic pumps where there has been a migration from tors extends the battery life of the device, allowing the cuscoreless motors to using brushless operation due to overall im- tomer longer time between charges or extended use of the deprovements in the price to performance of brushless motors. vice. This creates a better customer experience for the patient. The major differentiator for brushless motors is that applica"What we have done in terms of motor design over the last tions are able to achieve much higher speeds and longer life. few years has been focused on adding the ability to use neoTypical brushless speeds range from -10,000 to 50,000 RPM, dymium magnets to increase the power density. If the motor and can reach up to 100,000 RPM, compared to brush mois able to produce more power, it requires less power in for the tors speeds that are typically 12,000 RPM or lower. same equivalent power out. An additional benefit from a design standpoint with coreless DC motors is increased flexibilCoreless DC Motors ity in terms of motor diameters and motor lengths. The result From a DC motor standpoint, coreless motors are extremely is increased performance and tighter motor packages." easy to use because the application involves applying a voltage for the motor to produce the speed and torque. They're ideal Slotted DC Motors for portable devices because speed and torque are controlled In terms of brushless designs, another important category for by the voltage, requiring no electronics. portable medical device applications is slotted motors. With "The top design goals with portable devices are size and these motors, Portescap typically winds the core by hand to weight, and obviously the portable device needs to be easy for increase power density compared to slotless motors where the consumer or patient to use," said Beckstoffer. "The adthe core is automatically wound. Some benefits with a slotted vantage that coreless DC motors offer compared to a DC iron design are more flexibility in controlling the trade-off with core motor based on their construction is the fact that they are I2R losses and the ability for designers to maximize efficiency lighter weight and more efficient." compared to torque. Typically a slotted motor allows for betT8 T REND WAT C H : ME D I C A L / A S U P P L E M E N T T O D E S I G N NE WS MAY 2013 magenta cyan yellow black [www.designnews .com] ES245663_DNTW1305_T8.pgs 05.03.2013 01:32 UBM Source: Portescap M E D I CA L

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