Concentric Ball Screw Rotary Actuator With Interlaced Ball Recirculation
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Solution Overview
Problem
Conventional rotary actuators face challenges in achieving high torque efficiency and low friction, particularly in applications requiring compact and efficient rotary actuation, such as aircraft flight control surfaces and other industries.
Innovation Solution
A compact rotary actuator design featuring two concentric ball screws with an interlaced ball circuit, where one piston translates within an outer cylinder to cause opposite axial movement of the ball screws, recirculating ball bearings through shared paths, eliminating external ball return paths and reducing friction, and allowing for on-axis or off-axis positioning with mechanical links.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional acme screw assemblies are used to impart forces to a driven load, then the actuator can be simpler in structure, but high levels of friction along interfacing screw threads result in low torque efficiency and possible failure modes
Solution Approach 1:
The patent employs nested ball screws where an inner ball screw is positioned within an outer ball screw, both sharing common ball bearings and recirculation paths. This nested configuration allows the system to achieve high torque efficiency through ball bearing recirculation while maintaining a compact structure that does not significantly increase overall device complexity
Solution Approach 2:
The patent merges the recirculation functions of inner and outer ball screws by having them share common ball bearings and recirculation pathways. This consolidation reduces the total number of separate ball bearing sets and recirculation mechanisms needed, thereby maintaining structural simplicity while achieving high torque efficiency through the combined ball bearing recirculation system
2Force
If ball screw assemblies use low thread pitch to realize high linear force and translation, then output force is improved, but the actuator requires larger dimensions to accommodate the screw mechanism
Solution Approach 1:
By nesting the inner ball screw within the outer ball screw, the patent achieves a compact configuration where both screw mechanisms share the same radial space. This allows the actuator to maintain high force output capabilities while significantly reducing the overall volume and dimensions of the actuator assembly
Solution Approach 2:
The patent transitions from a conventional single-ball-screw configuration to a concentric dual-ball-screw arrangement, effectively utilizing the radial dimension to pack two high-force screw mechanisms into a compact volume. This dimensional arrangement allows high linear force generation without proportionally increasing actuator size
3Volume of moving object
If rotary actuators are made compact to reduce space requirements, then device size is reduced, but achieving high torque efficiency and low friction becomes more difficult
Solution Approach 1:
The nested ball screw configuration allows both inner and outer ball screws to share common ball bearings and recirculation paths within a compact volume. This arrangement maintains low friction and high torque efficiency by ensuring proper ball bearing recirculation while keeping the actuator size compact
Solution Approach 2:
By merging the recirculation systems of the inner and outer ball screws into shared pathways, the patent achieves efficient ball bearing recirculation for both screws within a compact actuator volume, thereby maintaining low friction operation without requiring a larger actuator size
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves high torque efficiency and low friction, enabling compact and efficient rotary actuation, reducing the need for mechanical linkages and underwing fairings, while maintaining reliability and adaptability across various applications.
Implementation Method 1
the ball bearings recirculate between the inner and outer ball screws through shared ball paths
Implementation Method 2
The rotary actuator may be employed as an on-axis or an off-axis solution for efficiently driving a revolute hinged joint... configured to provide high torque efficiency and low friction
Implementation Method 3
one or two pistons translate within an outer cylinder in response to admitted fluid pressure from an external pressure supply
Implementation Method 4
two concentric ball screws sharing/recirculating ball bearings therebetween... One of the ball screws is positioned radially within the other ball screw
Data Source
Figure 1
Figure 2A~2D
Figure 3
AI summary
A rotary actuator (200, 20) for a hinged panel assembly (190, 19), e.g., of a fixed-wing aircraft (10), includes ball bearings (42), an outer cylinder (126, 26), a piston (24), and an inner shaft (225, 25). The outer cylinder (126, 26) admits fluid pressure from a fluid pressure supply (15). The piston (24) is circumscribed by the outer cylinder (126, 26). The piston (24), outer cylinder (126, 26), and ball bearings (42) collectively forming an outer ball screw (29). The piston (24) translates along a longitudinal center axis (A20) in response to the fluid pressure. The inner shaft (225, 25) is circumscribed by the piston (24), with the inner shaft (225, 25), piston (24), and ball bearings (42) collectively forming an inner ball screw (29) that is concentric with the outer ball screw (29). The ball screws form an interlaced ball circuit (50) with one or more shared ball paths (40). Piston (24) translation rotates the piston (24) and inner shaft (225, 25), and to thereby recirculates the ball bearings (42) between the outer ball screw (29) and the inner ball screw (29) through the interlaced ball circuit.