Dual-Type Wave Gear Tooth Gap Layout for Wear and Fatigue Strength
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Solution Overview
Problem
Dual-type strain wave gearing faces challenges in enhancing wear resistance and fatigue strength due to uneven tooth-flank load distribution and stress concentration, which affects the transfer load torque and bearing durability.
Innovation Solution
Incorporating a rigid first and second internally toothed gear with a flexible externally toothed gear, featuring a gap between the first and second external teeth as a cutter clearance area, and optimizing the wave generator's support rigidity through equidistant ball bearing placement, to maintain uniform tooth contact and load distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the first and second external teeth are formed in the outer peripheral surface of a shared flexible cylindrical body with different tooth numbers, then the speed ratio can be easily realized as less than 50, but high stress concentration and large torsion occur in portions between the first and second external teeth
Solution Approach 1:
The externally toothed gear is divided into two separate flexible cylindrical bodies: a first flexible externally toothed gear and a second flexible externally toothed gear. Each gear has its own distinct tooth structure (first external teeth and second external teeth respectively), eliminating the stress concentration issues that occur when different tooth types share a single cylindrical body. This segmentation allows each gear to be independently optimized for its specific tooth configuration.
Solution Approach 2:
The problematic connection portions between first and second external teeth on the shared cylindrical body are completely removed. By extracting these high-stress connection zones and separating the gear structures, the design eliminates the source of stress concentration and torsion while maintaining the ability to achieve speed ratios less than 50 through the differential tooth counts of the two separate gears.
2Strength
If the tooth-flank load distribution is made uniform to increase tooth bottom fatigue strength, then the transfer load torque increases, but the support rigidity of the wave generator must be increased
Solution Approach 1:
Different wave generators are assigned to different gear functions: a first wave generator supports the first flexible externally toothed gear with first external teeth, and a second wave generator supports the second flexible externally toothed gear with second external teeth. Each wave generator can be independently designed with appropriate support rigidity tailored to the specific load characteristics of its associated gear, avoiding the need to uniformly increase support rigidity across the entire system.
Solution Approach 2:
The system uses two independently controllable wave generators that can dynamically adjust their support characteristics. This allows the support rigidity to be optimized for each specific gear-tooth configuration rather than requiring a single high-rigidity support structure, enabling uniform tooth-flank load distribution without proportionally increasing overall device complexity.
3Power
If the meshing states along the tooth trace direction are not appropriate, then the transfer load torque is decreased, but the bearing-ball load distributions become uneven
Solution Approach 1:
The bearing support system is segmented into two independent subsystems: a first wave bearing supporting the first wave generator and a second wave bearing supporting the second wave generator. This segmentation allows each bearing subsystem to be independently optimized for its specific gear's meshing characteristics, ensuring that bearing-ball load distributions remain even while maintaining appropriate meshing states for maximum transfer load torque.
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 enhances the wear resistance and fatigue strength of the externally toothed gear, improves the load transfer torque, and extends the service life of the wave generator by reducing torsion and stress concentration.
Implementation Method 1
a flexible externally toothed gear in which first external teeth capable of meshing with the first internal teeth and second external teeth capable of meshing with the second internal teeth are formed in an outer peripheral surface of a radially flexible cylindrical body
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
An externally toothed gear (4) of a dual-type strain wave gearing (1) is provided with first and second external teeth (7, 8) having different teeth numbers, and a gap (9) formed between these teeth as a cutter clearance area for tooth cutters. Where L1 is the maximum width of the gap (9), t1 is a depth from the tooth top land of the first external teeth (7) to the deepest part (9a) of the gap (9), h1 is the tooth depth of the first external teeth (7), t2 is a depth from the tooth top land of the second external teeth (8) to the deepest part (9a), and h2 is the tooth depth of the second external teeth (8), any one of the following conditions 1 to 3 is satisfied: Condition 1: L1=0.1L-0.35L, t1=0.9h1-1.3h1, and t2=0.3h2-0.9h2 Condition 2: L1=0.1L-0.35L, t1=0.3h1-0.9h1, and t2=0.9h2-1.3h2 Condition 3: L1=0.1L-0.35L, t1=0.3h1-0.9h1, and t2=0.3h2-0.9h2 It is possible to obtain a dual-type strain wave gearing in which wear resistance and tooth bottom fatigue strength are increased.