Among the challenges to advanced robotics and other mechatronic applications is the ability to get a range of precision motion with few components in a compact volume. The Mechatronic Screw Drive System utilizes the well-known principles of the screw, the planetary gear, and the roller bearing to create a solution for a low-part-count rotation-to-translation converter. There is an inherent safety feature to the design whereby the translation stops and can even reverse if patent load is exceeded.

Components of the Planetary Roller Screw Drive.

The core element of the Mechatronic Screw Drive Systems is the patented Planetary Roller Screw Drive (PRSD), initially developed to meet the needs for compact, highly efficient, and reliable actuators for the Rotex-Experiment of the German D2-SpaceLab mission. The PRSD combines the tried-and-true principles of the planetary gear and roller bearing in a unique fashion to create a new type of linear translator that transforms fast rotary motion into powerful, low-speed linear movement. The translator features 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. A PRSD with small effective pitch and high reduction ratio for travel-to-rotation can be created by the choice of roller bearings with different roller and screw diameters and opposite sense of pitch, thus adding the advantage of a reduction gear to the PRSD without adding additional parts.

When PRSDs are blended with brushless DC motors, the result is a compact, simple alternative to hydraulic and pneumatic actuators for a broad spectrum of applications ranging from intricate, small-range motion tasks, to automotive systems, to heavy lifting gear. The integration of position and force sensors into the PRSD translators is leading to a new generation of mechatronic devices with programmable impedance and dynamic behavior. The design of translators and actuators is fully supported by a powerful expert system for mechanical and control layout as well as for runtime simulations.

By selecting the material elasticity parameters and/or the profiles in such a way that the diameter of contact between the screw and the rollers changes with load, a translator with inherent safety is obtained, as the translation stops and even reverses if a preset load is exceeded. The translator is transformed to a position-impedance controlled actuator by fitting it with integrated absolute and incremental position sensors and a force sensor.

This technology was developed by DLR German Aerospace Center and is offered by yet2.com. For more information, view the yet2.com TechPak at http://info.hotims.com/ 45611-129 .


Motion Control & Automation Technology Magazine

This article first appeared in the December, 2013 issue of Motion Control & Automation Technology Magazine.

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