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Planetary roller-screw drive

by John Lewis, Regional Technical Editor -- Design News, January 7, 2002


By integrating PSRD translator, motor, and feedback technology, engineers have created a new class of actuator for applications ranging from intricate, small-range motion tasks to automtovie systems and heavy-lifting gear.

Achieving a range of precision motion with minimal components in a compact volume, the German Aerospace Research Center (DLR) has developed a series of electromechanical actuators designed around patented, planetary roller-screw drives (PRSD). Originally designed for a robotic-hand application, the PRSD combines a planetary gear, roller bearing, and motor technology to transform fast rotary motion into powerful, low-speed linear movement.

The translator structure includes three basic components: an outer cage, a spindle rod, and a planetary set of grooved rollers sandwiched in between. The combination of the outer cage and planetary roller set, linked to the cage by retainer rings, acts as a nut engaging the screw with markedly reduced friction, as the whole assembly constitutes a roller bearing.

Substituting roller bearings with different roller and screw diameters and different pitch directions allows engineers to change reduction ratios without increasing the number of components. Blending brushless dc motor technology with PSRD achieves a compact, simple alternative to hydraulic and pneumatic actuators. For programmable impedance and dynamic behavior in closed loop systems, engineers can integrate position or force sensors for feedback.

Martjin Rasser, Yet2.com 17 Monsignor O'Brien Hwy., Cambridge, MA 02141; Tel: (617) 557-3800 Ext. 127; Fax: (617) 523-8232; E-mail: mrasser@yet2.com.

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Submit your ideas and rough drawings for this section to John Lewis, Designer's Corner, Design News, 275 Washington St., Newton, MA 02458

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