Speed Reducer with Eccentric Shaft for Bearing Load Balancing
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Solution Overview
Problem
Existing speed reducers in trochoid systems face issues with whirling and precession due to uneven load distribution on bearings, leading to reduced bearing lifetime and increased manufacturing costs, especially when using cross roller bearings.
Innovation Solution
The implementation of multiple external gears assembled to an eccentric shaft, where moments are cancelled out by adjusting distances and loads, allowing for reduced internal moments on the output member, enabling the use of inexpensive ball bearings and reducing the size and thickness of the motor while extending bearing lifetime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single bearing is used to support the output member, then the device complexity is reduced, but the output member experiences whirling and precession due to unbalanced moments, reducing reliability
Solution Approach 1:
The patent divides the single bearing support into multiple bearing supports (first bearing and second bearing) to share the load and eliminate whirling. This segmentation of the support function resolves the contradiction by maintaining simplicity while improving stability through distributed support points.
Solution Approach 2:
The patent positions the external gear and output pins such that the moment generated by the external gear load is counterbalanced by the moment generated by the output pin reaction forces. This creates a self-balancing system where moments cancel each other, preventing whirling and precession without requiring complex additional components.
2Reliability
If cross roller bearings are used to support thrust and radial loads, then the reliability is improved, but the manufacturing cost increases significantly
Solution Approach 1:
The patent designs the gear and output pin arrangement to automatically balance moments and distribute loads in a way that standard ball bearings can handle. The system self-regulates the load distribution through its geometry, eliminating the need for expensive specialized bearings while maintaining reliability.
Solution Approach 2:
The patent changes the geometric parameters (distances, positions) of the gear and output pins to optimize load distribution. By carefully selecting these parameters, the moments are balanced and load capacities of standard bearings are sufficient, avoiding the need for costly cross roller bearings.
3Strength
If output pins are made longer to connect to the output member, then the strength is improved, but the moment arm increases causing greater moments and whirling
Solution Approach 1:
The patent positions the output pins and external gear such that the moment generated by the output pin forces counterbalances the moment from the gear load. This moment cancellation prevents whirling even with longer output pins, allowing the pins to be sufficiently long for strength without creating instability.
Solution Approach 2:
The patent resolves the moment issue by introducing axial positioning of multiple external gears at different locations. This transforms the problem from a two-dimensional moment arm issue to a three-dimensional balanced system where axial distribution creates counterbalancing moments.
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 effectively reduces internal moments and load deviations, preventing whirling and precession, thereby extending the lifespan of bearings and enabling a compact, durable motor with reduced manufacturing costs.
Implementation Method 1
the first external gear and the second external gear are assembled to the eccentric shaft in this order in the axial direction so that moments obtained by multiplying distances in an axial direction from a position of a center line of the outer bearing to center positions of the first external gear and the second external gear by loads acting on first output pins and second output pins at positions are cancelled out with one another
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
To provide an inexpensive and thin motor with a speed reducer capable of elongating lifetime of bearings by reducing the effect of internal moments acting on an output member without using expensive bearings. A motor with a speed reducer performing output with a gear mechanism rotating to reduce speed around an electric motor M and an eccentric shaft (8) driven to rotate by the electric motor M, in which a plurality of external gears (9), (10) are respectively assembled to the eccentric shaft (8) at positions where moments obtained by multiplying distances in an axial direction from a position of a bearing (12b) provided in a speed reducer housing (5) by magnitudes of loads acting on output pins (14) at the positions are cancelled out with each other.