Harmonic Drive Tooth Profile for Continuous Gear Engagement
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Solution Overview
Problem
In harmonic drive gears, the contact area between external and internal teeth is often insufficient, leading to decreased precision and torque due to non-continuous engagement of tooth-tops and tooth-roots, especially at points of increased flex spline deformation.
Innovation Solution
The use of similarity curves to generate tooth profiles for both external and internal teeth, where the tooth profile of the external teeth is enlarged based on positive-deviation moving paths and the internal teeth's profile is generated by further enlargement, ensuring continuous contact between tooth-tops and tooth-roots through a linear connection, even at increased deformation points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If tooth height is adjusted according to axial position for three-dimensional engagement, then engagement precision is improved, but engagement rate decreases at parts where flex spline deformation increases
Solution Approach 1:
The patent transitions from two-dimensional tooth profiles to three-dimensional tooth surfaces by introducing axial position as an additional dimension. The tooth profiles are defined by equations that include axial coordinate z, creating curved tooth surfaces that adapt to the flex spline's deformation throughout the axial length, thereby maintaining continuous contact in regions of high deformation.
Solution Approach 2:
The patent modifies the tooth profile parameters by introducing axial position-dependent variations. The tooth height, pressure angle, and profile shape are all made functions of axial position z, allowing the tooth geometry to change continuously along the axial direction to compensate for flex spline deformation and maintain optimal engagement conditions.
2Force
If contact area between external teeth and internal teeth is increased, then torque transfer is improved, but tooth-tops and tooth-roots may not come into continuous contact
Solution Approach 1:
The patent creates dynamically adaptive tooth surfaces that adjust their contact characteristics along the axial direction. The tooth profiles are designed to be curved in the axial direction, allowing the contact point to move smoothly from tooth-root to tooth-top regions as the flex spline deforms, ensuring continuous contact while distributing the load across the entire tooth surface for improved torque transfer.
Solution Approach 2:
The patent pre-configures the tooth profiles with predetermined curvature and shape variations along the axial direction that anticipate the flex spline's deformation pattern. By designing the tooth surfaces in advance to match the expected deformation, the system ensures continuous contact is maintained without requiring real-time adjustment during operation.
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 solution ensures continuous contact between external and internal teeth at points of increased flex spline deformation, enhancing precision and torque transfer in harmonic drive gears.
Implementation Method 1
The flex spline is formed of an elastically deformable material with external teeth disposed on its exterior. The flex spline rotates in connection with the wave generator. Since the flex spline is elastically deformed while rotating, the external teeth of the flex spline and the internal teeth of the circular spline are engaged with each other.
Data Source
AI summary
The present invention relates to a harmonic gear device in which a first similarity curve obtained by similarly transforming a reference curve representing a moving locus of an external tooth with respect to an internal tooth in a non-deflected state and a second similarity curve generated by similarly transforming the first similarity curve are used as a criterion for generating a tooth profile, wherein the present invention may provide the harmonic gear device that enlarges a first curve represented by a moving locus of positive deflection located above the apex of the reference curve among the moving loci of positive deflection of the external teeth on the basis of the reference curve to approximate an approximate reference point arranged on the second similarity curve to create a second curve, and uses the second curve as the top of the tooth profile of the external tooth.