Smart Actuators for Outstanding Load Carrying Capacity: Innovative Screw Drives for Electromechanical Linear Actuators

2015-02-03 | 000-005-561 DE-EN

SCHAEFFLER AG, BERLIN/SCHWEINFURT

Schaeffler at the Hannover Messe 2015 (Hall 22, Booth A 12)

Smart Actuators for Outstanding Load Carrying Capacity: Innovative Screw Drives for Electromechanical Linear Actuators

Schaeffler is expanding its range of spindles through the addition of a screw drive that features a new design and functional principle and delivers both a high load carrying capacity and a high power density. The technical characteristics of the so-called planetary screw drive or PWG make it the perfect addition to Schaefflers range, which includes the ball screw drive (KGT) and roller screw drive (RGT). The high power density of the PWG means that it can also be used as a substitute for hydraulic drives. Schaeffler thus has a complete range of screw drives and can deliver the perfect solution for every application in terms of speed, precision, and load carrying capacity. The planetary screw drive (PWG) paves the way towards smart actuators: Electromechanical linear actuators that combine the highest possible efficiency with the smallest possible design envelope.

The ball screw drive and roller screw drive have both become well established on the screw drive market. The ball screw drives outstanding strengths include high dynamics due to the high spindle pitch, low-friction running, and a high level of positioning and repeat accuracy. For geometrical reasons, however, low spindle pitches cannot be achieved. By comparison, the roller screw drive offers a higher load carrying capacity at spindle pitches from approx. 10 mm and high positioning accuracy.

The missing third element is a design that can support even higher loads at small spindle pitches of less than 5 mm. For this type of application, Schaeffler has developed the so-called planetary screw drive (PWG): This design features planetary gears with v-shaped parallel grooves that roll up and down the spindle. The rotation of these planetary gears and the planetary screw drive is ensured by the two-piece screw drive nut, which also has grooves at the ends that engage with the ends of the planetary gears. The very high number of rolling contacts means that the PWG achieves a higher load carrying capacity and rigidity than the other two designs. Friction levels remain low thanks to the good internal load distribution and the optimized osculation between the spindle thread flanks and the crowned flanks of the planetary gear grooves. When planetary gears with the correct groove diameter are selected, overall pitches of just 0.75 to 5 mm can be achieved.

The special features of this design include the manufacturing process itself: The spindles and planetary gears are manufactured using forming methods, which makes good material compression possible together with optimum grain flow, the highest possible strength, and therefore a further 15% increase in load rating compared to conventional technologies. This manufacturing method also reduces the costs to a level comparable with that of ball screw drives manufactured using forming methods. Clearance free, preloaded units can easily be created by adding a spacer washer between the two halves of the spindle nut.

Reduced design envelope, higher power density, and cost savings

The PWG closes the gap between the RGT and KGT in the spindle diameter range between 5 and approximately 30 mm when it comes to very high load carrying capacities and the smallest possible overall pitches. For example, the PWG generates an impressive 200 N of axial force from only 40 Ncm with an overall pitch of 0.75 mm. Consequently, very high axial forces can be achieved even with small motors. Schaefflers planetary screw drive (PWG) thus makes it possible not only for actuators driven my electric motors with a high power density, long rating life, and low maintenance outlay to be developed, but also for low-cost motors to be used. The electric drive can be easily integrated using a feather key connection on the outside diameter of the spindle nut.

Applications and initial projects can be found in areas like mirror tracking systems in the solar power sector, azimuth adjustment systems in the wind power sector, feed units for sheet metal forming in the mechanical engineering sector, in sheet metal bending machines, in locking cylinders for plastic injection molding machines, in riveting and cutting devices, and in adhesive metering systems. The PWG is already in volume-production use in clutch actuators for the automotive industry.

LINK:	http://www.ina.de/content.ina.de/en/press/press-releases/press-details...
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