Eccentric Oscillation Gear Fastening for Stable Axial Tension
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Solution Overview
Problem
Conventional eccentric oscillation gear devices experience instability due to variations in frictional force among fasteners, leading to uneven axial tension and preload in main bearings, affecting rotational stability and accuracy.
Innovation Solution
The use of a fastening system with an externally threaded fastener of Rockwell hardness HRC 44 or higher and an internally threaded portion of lower hardness, allowing for plastic deformation of thread surfaces to increase contact area and stabilize axial tension, ensuring consistent preload and reduced frictional variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fasteners with uniform hardness are used to fasten the hold and shaft portion, then the fastening structure is simple, but the frictional force varies among fasteners causing instability in axial tension
Solution Approach 1:
The patent applies different hardness values to different components of the fastening system. Specifically, the fastener is made with higher hardness (HRC44 or higher) while the internally threaded portion is made with lower hardness. This local differentiation of material properties ensures that the harder fastener can plastically deform the softer internally threaded portion, increasing contact area and stabilizing frictional force across all fasteners, thereby resolving the axial tension instability without requiring complex additional structures.
2Reliability
If the fastener has high hardness to increase contact area through plastic deformation, then the contact area increases and frictional force stabilizes, but the internally threaded portion must have lower hardness which may reduce its strength
Solution Approach 1:
The patent carefully controls the hardness parameters of both the fastener and internally threaded portion. The fastener has hardness of HRC44 or higher, while the internally threaded portion has lower hardness but within a controlled range that maintains sufficient strength. This parameter optimization allows the softer internally threaded portion to undergo controlled plastic deformation that increases contact area and stabilizes friction, while still maintaining adequate structural strength for the application.
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 stabilizes axial tension, evenly preloads main bearings, and enhances rotational stability and torque density, improving the positional and trajectory accuracy of robots and industrial machines.
Implementation Method 1
The threads of the externally threaded portion having the above-mentioned hardness can plastically deform the rough surface or micro projections of the threads of the internally threaded portion when the first and second members are fastened.
Data Source
AI summary
An eccentric oscillation gear device includes a casing, a first member supported by the casing via a first bearing, a second member supported by the casing via a second bearing, and a fastening portion fastening the first and second members in an axial direction of the casing. The fastening portion includes an internally threaded portion formed in the first member, and a fastener having an externally threaded portion. The fastener has a Rockwell hardness (HRC) of 44 or higher, and the internally threaded portion has a lower hardness than the fastener.