Compound Harmonic Gear Actuator Backlash Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional compound harmonic drive assemblies in aircraft rotary actuators face challenges in reducing backlash and vibration while maintaining high reduction ratios, particularly in applications requiring large torque and precise control of flight surfaces.
Innovation Solution
The compound harmonic actuator incorporates a wave generator with a scalloped outer surface and roller bearings, a single unitary flex spline, and a coupling system to securely interface with multiple ring gears, allowing for efficient torque transmission and reduced cyclic stresses, thereby enhancing the actuator's ability to control aircraft surfaces with high precision and torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a compound harmonic drive is used to achieve high reduction ratios with concentric shafts, then the speed reduction capability is improved, but backlash and vibration increase
Solution Approach 1:
The wave generator is segmented into multiple lobes (typically 2-4 lobes) around its circumference, with each lobe engaging a corresponding number of teeth on the flex spline. This segmentation allows the harmonic drive to achieve high reduction ratios while distributing the meshing forces across multiple engagement points, thereby reducing vibration and backlash compared to single-point engagement mechanisms.
Solution Approach 2:
The flex spline is constructed as a thin-walled elastic component that can deform elastically under the action of the wave generator. This flexibility allows the flex spline to conform to the elliptical shape imposed by the wave generator, enabling smooth continuous motion transmission with minimal backlash. The elastic deformation absorbs vibrations and allows for precise tooth engagement without the gaps typical in rigid gear systems.
2Object-generated harmful factors
If the wave generator imparts continuously moving elliptical form to the flex spline, then the meshing of teeth progresses in rolling fashion reducing backlash, but the cyclic stresses increase causing fatigue
Solution Approach 1:
The wave generator creates a periodic elliptical deformation pattern in the flex spline that repeats with each rotation. This periodic action ensures that any cyclic stresses are distributed uniformly across all teeth of the flex spline over time, preventing stress concentration at single points. The regular rhythm of engagement and disengagement allows for predictable fatigue loading that can be designed into the component's lifespan.
Solution Approach 2:
The elliptical shape parameters of the wave generator (major axis, minor axis, lobe count) are carefully optimized to control the magnitude and distribution of cyclic stresses in the flex spline. By adjusting these geometric parameters, the design balances the need for smooth rolling meshing (which reduces backlash) with the need to limit stress amplitudes (which prevents fatigue). The thickness and material properties of the flex spline are also tuned to accommodate the cyclic deformation without excessive stress.
3Power
If roller bearings are arranged circumferentially about the scalloped outer surface of the wave generator, then the torque transmission is improved, but the device complexity increases
Solution Approach 1:
The roller bearings are integrated directly into the scalloped outer surface geometry of the wave generator, merging the bearing support function with the wave-generating geometry. The scallops themselves serve as bearing races, eliminating the need for separate bearing housings or mounting structures. This integration maintains high torque transmission capability while reducing the number of discrete components and simplifying the overall assembly.
Solution Approach 2:
The scalloped outer surface of the wave generator serves multiple functions: it generates the elliptical wave motion in the flex spline, provides structural support for the roller bearings, and transmits torque from the input shaft to the flex spline. By combining these functions into a single component geometry, the design achieves high torque transmission without proportionally increasing complexity, as the same structural features perform multiple roles.
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
This configuration reduces backlash and vibration, enabling precise control of aircraft surfaces with improved torque transmission and reduced fatigue, thus enhancing the performance of aircraft actuation systems.
Implementation Method 1
roller bearings arranged circumferentially about the scalloped outer surface
Implementation Method 2
roller bearings arranged circumferentially about the scalloped outer surface
Implementation Method 3
The wave generator is rotatably drivable by the motor and shaped to form the flex spline into an elliptical shape
Data Source
AI summary
A compound harmonic actuator is provided and includes a motor, a flex spline disposed about the motor and a wave generator radially interposable between the motor and the flex spline. The wave generator being rotatably drivable by the motor and shaped to form the flex spline into an elliptical shape with an axis such that wave generator rotations drive rotations of the axis of the ellipse of the flex spline.