Direct drive electromechanical linear actuators

Abstract

Direct drive electromechanical rotary-to-linear actuators include one or more electric motors mounted in a housing. Each motor includes a stator and a rotor. The motor drives a planetary drive mechanism that includes an elongated central shaft having one or more helical threads on an external surface coupled to the rotor for conjoint rotation. A planetary nut having helical threads on an internal surface is disposed concentric to the shaft, and a plurality of planetary rollers are disposed concentrically between the shaft and the planetary nut. Each of the rollers has a helical thread on an external surface that is complementary to and in engagement with a thread of the shaft and a thread of the nut. Rotation of the rotor is converted with mechanical advantage into linear movement of the planetary nut. The actuators provide backlash-free operation, higher stiffnesses, slew rates and frequency responses, and better overall efficiency.

Description

TECHNICAL FIELD [0001] This invention relates to motion control or actuation devices in general, and in particular, to direct drive electromechanical rotary-to-linear motion actuators. BACKGROUND [0002] Electromechanical actuators are rapidly displacing hydraulic devices in a wide range of industries, including aviation. Improvements in solid state switching devices, their digital control and in the performance of magnetic materials have all contributed to an increased interest in electric actuators. Electromechanical linear actuators are particularly well suited to flight control applications, as well as a multitude of industrial uses, particularly in production automation. Automotive and other vehicle applications also abound, as may be found, for example, in the variable transmissions and caliper or disk brake actuators described in, e.g., U.S. Pat. Nos. 6,837,818 and 6,626,778 to Kapaan et al., and 6,367,597 and 6,318,512 to De Vries et al. [0003] Flight applications, such as ac...

AI Technical Summary

Benefits of technology

[0015] Means are provided for releasably holding the spool in the first position during normal operation of the actuator. In a simple yet reliable implementation, these means can comprise a plurality of ball bearings disposed in apertures in the spool and held captive in an adjacent circumferential groove by an arm of a solenoid. The same solenoid can be used to selectably release the spool from the first position for movement to the second position, e.g., in response to a malfunction of the main motor, whereupon the actuator rapidly switches to a “fail operational” mode in which the backup motor takes over operation of the actuator from the malfunctioning main motor.

[0017] In an alternative embodiment, the rollers can be located in adjacent planes perpendicular to the spindle, each plane containing a radially symmetrical array of two or more rollers. In another advantageous variation, the wall of the drum can be strained from a cylindrical shape to a trochoidal shape incorporating a plurality of longitudinal zones having a smaller radius alternating with a plurality of longitudinal zones having a larger radius. The resulting beam-bending thereby imposed in the wall of the drum, coupled with the stiffening effect of the corrugations therein, provides an inward-directed restoring force that engages the rollers in diametral compression between the walls of the drum and the motor spindle.

Problems solved by technology

These problems include backlash, wear, complexity and cost and life limitations.

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