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issue: September 2006 APPLIANCE Magazine

Motor Technology
Stepping Inside

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From the outside, the new SST43D motor may appear to be a standard NEMA 17 stepper, but a redesigned interior reportedly provides NEMA 23 performance.

The SST43D from SKC (Culver City, California, U.S.) is said to offer high torque without consuming large amounts of power. “Because this motor is more energy efficient, it converts the input energy into more usable work turning the motor shaft driving the design,” explains Nao Yamashita, senior applications engineer. “Since it converts energy better, you gain more torque for the same input power given.”

According to Shinano Kenshi Corporation (SKC), maker of brushless DC motors and stepper motors, its new SST43D stepping motor is not a standard NEMA 17 model. Of course, the motor meets all necessary specs, but a proprietary rotor design is said to enable a range of competitive features, including high torque and low audible and frequency noise.
Nao Yamashita, senior applications engineer, says the motor’s new interior design resulted in higher conversion of input power into usable output shaft torque. “We enlarged the rotor area slightly and reduced the area for stator region, while adjusting the profile of the rotor and stator teeth to help focus the magnetic flux in the air gap,” Yamashita explains. “The resulting optimum balance of rotor/stator area and more focused teeth achieved the extra torque and better smoothness and vibration characteristics.”
In fact, the new motor reportedly has 30 percent more torque than its predecessor, with 3 dB to 6 dB lower audible noise for a motor with equal torque. Yamashita says the majority of the torque increase was created by enlarging the rotor area, which allowed for more magnetic materials and a stronger field. The balance of the torque increase was achieved with the better tooth profile. This helps the motor operate smoother, with less pole ringing and, thus, more usable torque for the application. This also makes the motor quieter, although noise improvement is based on the motor speed.
SKC says it built a smaller NEMA 17 motor with the power of a NEMA 23 motor to help customers save costs. “Every application will save motor cost within the design if they can downsize from one stack length to a shorter one, which uses less material,” Yamashita notes. “This achieved without changing any current settings or drive methods within any design, existing or new.” Of course, achieving the necessary power required adding more magnetics, but Yamashita says no expensive, extra high-powered materials were used. Instead, the company utilized more of the magnetic material it already uses in great quantities during production. The motors are also designed to be built on newer, more-productive automated manufacturing lines, further reducing cost.
Yamashita says that it is important for design engineers to remember that there have been no changes in the physical size of the motors, so there is no need for spatial packaging concerns. “Engineers will find more power from a given body length unit,” he says. “They can use that power in many ways—use the higher torque headroom and take the safety margin, run at higher speeds because the motor has more torque to give, or reduce the current to the motor by 30 percent, resulting in equal torque but with less power supply requirements, less motor heating because underdriving below rated current and longer life because of the less heat on the bearings.”
End applications for the RoHS-compliant stepper include high-speed printing applications, medical IV pumps, DVD peripheral products, and surveillance security cameras. They are available in D1 and D2 heights and come standard with an integrated connector.

Suppliers mentioned in this article:
Shinano Kenshi Corp.

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