Patent Application
20110138949
The subject matter disclosed herein generally to the field of linear actuators.
A linear actuator is a machine designed to provide force and linear displacement to an object. A linear actuator may comprise an electromechanical actuator (EMA), wherein the actuator is powered by an electric motor. EMAs offer increased efficiency over hydraulic or pneumatic linear actuators while eliminating fire hazards and leakage problems associated with hydraulic fluids used in hydraulic actuation systems.
A linear actuator may comprise a ball screw actuator, in which an electric motor powers a rotating ball bearing screw, or ball screw. A ball screw actuator converts rotary motion from a rotating ball screw into linear motion by a translating nut via a spiral ball track. As the ball screw is rotated, the translating nut, which is engaged with the ball screw, is restrained from turning, and a set of ball bearings located between the screw and nut are forced to follow the spiral ball track, reducing friction between the ball screw and the nut. The nut is thereby translated in a linear direction by the rotation of the ball screw.
In order to restrain the translating nut from turning with the ball screw's rotation, a ball screw actuator requires that the torque associated with the rotating ball screw be reacted. The simplest way to react the driving torque is to utilize the structure associated with the actuator load. Ball screw actuators are typically used for applications in which the object being moved articulates on a structure that has a predetermined path; such a structure may be used to inhibit the rotation of the translating nut. However, in some applications, it may not be possible for the ball screw actuator to react the torque into the parent structure. In such an application, a torque reacting element, such as external torque reacting linkage or a torque reacting spline, may be incorporated into the actuator. In applications where the actuator may not incorporate an external torque reacting linkage (for example, due to packaging constraints), the torque reacting spline may be used. A torque reacting spline comprises a sliding interface located between the stationary and translating elements of the actuator, which accommodates the translating element's translation while reacting the torque from the rotating element. However, the sliding friction associated with a torque reacting spline's sliding interface absorbs energy from the system, reducing the actuator's overall efficiency. The torque reacting spline may also experience relatively high wear due to the sliding friction.
According to one aspect of the invention, a linear actuator includes a ball screw, the ball screw configured to rotate; a nut engaged with the ball screw, the nut configured to translate linearly in response to the rotation of the ball screw; and a ball bearing spline integrated into the nut, the ball bearing spline comprising a plurality of ball bearings, wherein the ball bearing spline is configured to react a torque from the rotation of the ball screw.
According to another aspect of the invention, a ball bearing spline is integrated into a translating nut of a linear actuator, the ball bearing spline comprising a plurality of ball bearings, wherein the ball bearing spline is configured to react a torque from a rotation of a ball screw engaged with the translating nut.
Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings.
Referring now to the drawings wherein like elements are numbered alike in the several FIGURES:
Embodiments of a linear actuator comprising a ball bearing spline are provided, with exemplary embodiments being discussed below in detail.
A ball bearing spline may be incorporated into the translating element, or nut, of a linear ball screw actuator. The ball bearing spline comprises a linear race that holds a plurality of rolling elements, or ball bearings. The ball bearings act to transfer a load linearly across the interface between the stationary housing and the translating nut while reacting the ball screw torque with relatively low friction, thereby increasing the efficiency of the actuator. A bearing ball spline may comprise a ball return, allowing the ball bearings to recirculate in the race by forcing ball bearings that exit the ball bearing spline's load path back to the entrance to the load path, allowing the ball bearing spline to operate over an unlimited stroke.
The technical effects and benefits of exemplary embodiments include a linear actuator spline having increased efficiency and decreased wear.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while various embodiment of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
