Compound Planetary Gear Actuator for High Reduction and Back-Drivability
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Solution Overview
Problem
Conventional actuators face limitations in providing a high reduction gear ratio, leading to increased size and complexity, while also experiencing high frictional forces and low reverse driving characteristics, which are essential for sophisticated operations like robot control.
Innovation Solution
A planetary gear actuator design featuring a sun gear, rotary internal gear, fixed internal gear, and compound planetary gears with specific tooth configurations and arrangements, allowing for a high reduction gear ratio, reduced volume, lower frictional force, and improved back-drivability, while minimizing the number of components and processing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple stages of speed reduction are used to achieve high reduction gear ratio, then the reduction gear ratio is improved, but the size and structural complexity of the actuator increases
Solution Approach 1:
The patent combines multiple planetary gear stages into a single integrated planetary gear set, merging the functions of multiple speed reduction stages into one unified structure. This allows achieving high reduction gear ratio (e.g., 1:100 or higher) without requiring multiple separate reduction stages, thereby reducing structural complexity while maintaining high productivity.
Solution Approach 2:
The patent employs a nested configuration where planetary gears are arranged concentrically around a sun gear, with planet gears mounted on a carrier that rotates around the sun gear. This nested arrangement allows multiple gear interactions (sun gear with planet gears, planet gears with ring gear) to occur within a compact volume, achieving high reduction ratio in a single stage without increasing overall structural complexity.
2Productivity
If conventional planetary gear structures are used, then the actuator can provide speed reduction, but the frictional force is high and reverse driving characteristic is low
Solution Approach 1:
The patent optimizes the local quality of gear tooth surfaces through precise tooth profile design and appropriate material selection, reducing frictional losses at critical contact points. The planetary gear set is designed with optimized tooth geometry and surface treatments that minimize friction while maintaining high load capacity, thereby reducing energy loss without compromising speed reduction capability.
3Volume of moving object
If the actuator volume is reduced, then compactness is improved, but the number of components and processing cost may increase
Solution Approach 1:
The patent merges multiple functional components into fewer parts, such as integrating the carrier structure with support functions and using a unified planetary gear assembly that combines multiple gear stages. This reduces the total number of discrete components, simplifying assembly and reducing processing costs while achieving compact actuator volume.
Solution Approach 2:
The planetary gear set is designed with multi-functional components that perform multiple roles simultaneously. For example, the carrier not only supports the planet gears but also provides structural support and mounting functions. This multi-functionality reduces the number of dedicated components needed, lowering manufacturing complexity and cost while maintaining compact dimensions.
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 achieves a higher reduction gear ratio, increased rotary power, lower frictional force, and higher efficiency compared to conventional structures, with a smaller volume and reduced component count, enhancing the actuator's performance and cost-effectiveness.
Implementation Method 1
a pin bearing inserted into a through hole extended in a thickness direction of the first planet gear, and arranged in the first and second extension portions
Data Source
AI summary
A planetary gear actuator including a sun gear, a rotary internal gear being concentric with the sun gear, a fixed internal gear being concentric with the sun gear, compound planetary gears, and a carrier connected to each of the compound planetary gears so as to be rotatable relative to each of compound planetary gears may be provided, Each of the compound planetary gears may include a first planet gear engaged with the sun gear, a second planet gear at one side of the first planet gear, engaged with the rotary internal gear, and having a smaller number of teeth than the first planet gear, and a third planet gear at another side of the first planet gear, engaged with the fixed internal gear, and having a smaller number of teeth than the first planet gear. One compound planetary gear may overlap another compound planetary gear in a thickness direction.