Parallel Eccentric Rotary Actuator with Circular Arc Gears
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Solution Overview
Problem
Existing parallel eccentric rotary actuators face inefficiencies due to high sliding friction, high internal force magnification, and low stiffness, which limits their effectiveness in complex duty cycles requiring high torque density, high efficiency, and shock resistance, especially in applications like fighter aircraft control and construction machinery.
Innovation Solution
A simplified parallel eccentric rotary actuator design featuring circular arc gear teeth, reduced rolling element bearings, Oldham crosslinks with high contact surface stiffness, and a pancake configuration with lightly loaded bearings to achieve high torque density and shock resistance, while minimizing weight and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard compound gears with parallel shafts are used, then manufacturing is simplified using AGMA standards, but sliding friction increases and torque density decreases
Solution Approach 1:
The patent employs circular arc gear teeth instead of standard involute teeth, creating curved contact surfaces that reduce sliding friction. The circular arc profile allows for more favorable contact geometry between mating gears, transforming the friction characteristics while maintaining manufacturability through specialized but not excessive complexity
Solution Approach 2:
The invention changes the fundamental gear tooth geometry parameters from standard AGMA involute profiles to circular arc profiles with specific radius ratios. This parameter change fundamentally alters the friction and contact characteristics, enabling reduced sliding friction while maintaining the parallel shaft configuration
2Power
If parallel eccentric gear reducers are used, then torque density improves, but device complexity increases with multiple crankshafts and bearings
Solution Approach 1:
The patent combines multiple eccentric mechanisms into a single integrated crankshaft structure with multiple eccentrics positioned at different angles. This merging of functions reduces the number of separate components (fewer crankshafts and bearing sets) while maintaining the torque density benefits of parallel eccentric gearing
Solution Approach 2:
The single crankshaft with multiple eccentrics serves multiple functions simultaneously: it drives multiple parallel eccentric gears, provides synchronized motion control, and reduces overall structural complexity. This multi-functional design element replaces what would traditionally require multiple separate driving mechanisms
3Stability of the object's composition
If rolling element bearings are used in parallel eccentric actuators, then support and stability improve, but weight increases and shock resistance decreases
Solution Approach 1:
The patent removes rolling element bearings from the eccentric gear support positions and replaces them with alternative support mechanisms such as journal bearings or direct journal contacts. This extraction of the rolling element bearing component reduces weight and increases shock resistance while maintaining adequate support through the alternative bearing arrangement
Solution Approach 2:
The design employs simpler, lighter bearing solutions that may have shorter service lives but provide adequate support for the application requirements. These simpler bearing elements reduce overall actuator weight and allow for easier replacement, trading long service life for reduced weight and improved shock characteristics
4Ease of manufacture
If conventional gear teeth profiles are used, then manufacturing is straightforward, but contact ratio is limited to slightly more than 2 teeth
Solution Approach 1:
The circular arc tooth profile creates extended contact paths between mating gears, allowing more teeth to be in contact simultaneously compared to standard involute profiles. The curved geometry naturally increases the contact ratio while maintaining manufacturability through specialized cutting processes that are not excessively complex
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 provides exceptional rigidity, high torque density, and reduced inertia, enabling effective operation in complex duty cycles with improved responsiveness and reduced maintenance needs, making it suitable for replacing hydraulic systems in heavy-duty applications.
Implementation Method 1
circular arc gear teeth
Implementation Method 2
high sliding friction
Implementation Method 3
Oldham crosslinks with high contact surface stiffness
Implementation Method 4
reduced rolling element bearings
Data Source
AI summary
A rotary actuator (101) is provided which includes first and second opposing endplates (107); a stator (105) having a first end which is attached to said first endplate, and a second end which is attached to said second endplate; a rotor (103) having first and second eccentrics (125) on a surface thereof; an output attachment ring gear (135) disposed about the periphery of said first and second opposing endplates; a first parallel eccentric gear (131) which is disposed between said first eccentric and said output gear and which meshes with said output gear; a second parallel eccentric gear which is disposed between said second eccentric and said output gear and which meshes with said output gear; a first crosslink (113) which engages said first endplate and said first eccentric gear by way of a first set of surface features (143, 153); and a second crosslink which meshes with said second endplate and said second eccentric gear by way of a second set of surface features. The rotary actuator further includes a star compound gear train which includes a star gear which is in mesh with the output gear across a second mesh, wherein the first mesh is radially separated from the second mesh across an open space.