Modified Parallel Eccentric Rotary Actuator Gear Train

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Solution Overview

Problem

Existing rotary actuators face challenges with torque density, lost motion, stiffness, efficiency, complexity, and cost effectiveness due to the use of cycloidal wave/pin mesh and involute gear teeth, which result in high internal forces, deformations, and inefficiencies.

Innovation Solution

The Modified Parallel Eccentric (MPE) gear train employs circular arc gear teeth and a simplified structure with a central crankshaft driving two parallel eccentric gears, using rolling element bearings and Oldham couplings with embedded splines to reduce friction and wear, eliminating the need for front-end gears and minimizing internal bearings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If cycloidal wave/pin mesh and involute gear teeth are used in rotary actuators, then the actuators can achieve rotational motion, but they suffer from high internal forces, deformations, and inefficiencies resulting in low torque density and high complexity

Engineering Contradiction:

Improvetorque densityVSAvoidgear train complexity

Core Design Contradiction:

PowerVSDevice complexity

Solution Approach 1:

The gear train is segmented into modular components: a crankshaft with eccentrics, parallel oscillating gears, and a hypocyclic gear set. This segmentation allows each component to be optimized independently, reducing overall complexity while maintaining high torque density. The parallel eccentric gears are divided into multiple teeth that engage sequentially with the hypocyclic gear, distributing loads and reducing internal forces.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent inverts the traditional gear train architecture by using a crankshaft-driven parallel eccentric mechanism instead of conventional motor-driven gearboxes. The crankshaft converts rotational motion to oscillating motion, which then drives the hypocyclic gear train in reverse of typical configurations, achieving higher torque density with fewer components.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If traditional cycloidal/pin drives are used, then rotational motion is achieved, but lost motion and low stiffness occur

Engineering Contradiction:

ImprovestiffnessVSAvoidlost motion

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The hypocyclic gear teeth are designed with curved profiles that conform to spherical geometry principles, ensuring continuous contact and eliminating backlash. The oscillating parallel gears engage with the stationary hypocyclic gear through curved tooth profiles that maintain constant velocity ratios, preventing lost motion and enhancing stiffness.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The gear train maintains continuous engagement of multiple teeth between the oscillating parallel gears and the stationary hypocyclic gear throughout the oscillation cycle. This continuous multi-point contact ensures no lost motion occurs and maintains high stiffness throughout the entire range of motion.

Inventive Principle:

Principle #20Continuity of useful action

3Productivity

If conventional gear trains with multiple bearings are used, then structural support is provided, but friction and wear increase reducing efficiency

Engineering Contradiction:

ImproveefficiencyVSAvoidfriction loss

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent extracts and eliminates unnecessary bearings from the gear train by using a simplified crankshaft-supported parallel eccentric mechanism. Only essential bearings remain at critical locations, removing sources of friction and wear while maintaining structural support. The oscillating gears are directly supported by the crankshaft eccentrics without intermediate bearings.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The oscillating parallel gears serve their own support function through direct engagement with the crankshaft eccentrics, eliminating the need for separate bearing structures. The gear teeth themselves provide the necessary support and positioning, reducing friction points and improving overall efficiency.

Inventive Principle:

Principle #25Self-service

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 MPE gear train achieves higher torque density, reduced lost motion, increased stiffness, and improved efficiency by up to 5 times compared to traditional cycloidal/pin drives, with a 3 to 4 times increase in torque density and 6 to 8 times greater output stiffness, while minimizing deformation and operational costs.

Implementation Method 1

using rolling element bearings and Oldham couplings with embedded splines to reduce friction and wear

Methodology Applied

Scientific EffectRolling element bearing: Ball Bearing

Implementation Method 2

The MPE gear train employs circular arc gear teeth and a simplified structure with a central crankshaft driving two parallel eccentric gears

Methodology Applied

Scientific EffectGear teeth contact: Gear

Data Source

PatentUS10655706B2Modified parallel eccentric rotary actuator

Publication Date: 2020.05.19 FATHOM5 CORP

AI summary

A rotary actuator is provided which includes an internal gear, first and second parallel eccentric gears which mesh with said internal gear, a crankshaft equipped with first and second eccentrics which are 180° out-of-phase and which drive said first and second parallel eccentric gears, respectively, a prime mover which drives said crankshaft, first and second crosslinks which prevent the rotation of said first and second parallel eccentric gears, respectively, and first and second sets of splines which engage said first and second parallel eccentric gears, respectively.