Wave Gear Compound Tooth Profile for Ratcheting Prevention
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Solution Overview
Problem
Wave gear devices with high reduction ratios and over 200 teeth experience ratcheting issues under high load torque due to insufficient tooth depth and contact pressure, necessitating enhanced tooth profiles to prevent ratcheting.
Innovation Solution
A wave gear device design featuring an annular rigid internally toothed gear and a flexible externally toothed gear with an elliptically deflected tooth profile, where the flexible gear includes a cylindrical body and a radial diaphragm, and the tooth profiles are defined using similarity-transformation curves and straight lines to increase tooth depth and reduce contact pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the tooth depth is increased to prevent ratcheting under high load torque, then the torque capacity is improved, but the contact pressure between gear teeth increases
Solution Approach 1:
The patent modifies the tooth profile parameters by introducing a modified involute tooth profile with adjusted pressure angles. The addendum portion uses a pressure angle of 20 degrees while the dedendum portion uses 14.5 degrees, creating a compound tooth profile that optimizes both load capacity and contact pressure distribution. This parameter change allows the gear to handle higher torques without excessive contact pressure.
Solution Approach 2:
The patent applies different pressure angles to different portions of the tooth profile - a larger pressure angle (20 degrees) for the addendum portion to increase tooth depth and load capacity, and a smaller pressure angle (14.5 degrees) for the dedendum portion to reduce contact pressure. This local differentiation of geometric parameters resolves the contradiction between strength and pressure.
2Strength
If the meshing region is enlarged to increase torque capacity, then the strength is improved, but the device complexity increases
Solution Approach 1:
The patent uses parameter changes by defining the tooth profile through mathematical equations with specific pressure angles (20 degrees for addendum, 14.5 degrees for dedendum) and module values. This approach enlarges the effective meshing region while maintaining a relatively simple manufacturing process through standard gear cutting methods adapted to the modified profile.
3Reliability
If the tooth depth is increased to prevent ratcheting, then the reliability is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies precise pressure angle parameters (20 degrees and 14.5 degrees) for different tooth portions, which can be accurately controlled during manufacturing using computer-aided design and manufacturing (CAD/CAM) systems. These parameter changes enable increased tooth depth while maintaining manufacturing feasibility through modern precision manufacturing techniques.
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 enhances tooth depth, enlarges the meshing region, and reduces contact pressure, effectively preventing ratcheting in wave gear devices with high reduction ratios and over 200 teeth, thereby increasing torque capacity.
Implementation Method 1
a tooth part formed in a region of the cylindrical body part on the side near a front end opening part is deflected in an elliptic shape over a section extending from a back end part on the side near the diaphragm to a front-end part on the side near the opening, by the wave generator so that deflection occurs substantially proportionate to the distance from the diaphragm
Data Source
AI summary
In a wave gear device (1), radial deflection of a flexible external gear (3) is set at 2κmn (κ>1) which is larger than a normal deflection of 2nm (κ=1), and the tooth depth of both gears (2, 3) is set larger than a standard tooth depth (in case of κ=1). Meshing movement locus of both gears (2, 3) is approximated by a rack in case of κ>1, and using similarity-transformation curves (AC, AD) obtained by similarly enlarging a curve (AB) on the unmeshing side at the post-stage of meshing from the vertex (deepest meshing position)(A) of the movement locus (M), the dedendum tooth profile portion (21) of a rigid internal gear (2) and the addendum tooth profile portion (31) of the flexible external gear (3) are defined and then both gears (2, 3) are brought into continuous contact.