Bearingless Planetary Gearbox with Compound Planets
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Solution Overview
Problem
Conventional robotic gearbox systems face limitations in achieving high torque density, compactness, and low backlash due to high manufacturing complexity, cost, and weight, particularly in applications requiring wide reduction ratios and high precision, such as robotic joints and space applications.
Innovation Solution
A bearingless planetary gearbox design featuring two planetary stages that share compound planets, eliminating the need for a planet carrier and bearings, allowing for a floating structure that reduces mass, cost, and manufacturing complexity while achieving high efficiency and a wide range of reduction ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional planetary gearboxes use bearings and planet carriers to support planet gears, then the structure is stable and reliable, but the device complexity, weight, and manufacturing cost increase
Solution Approach 1:
The patent removes the planet carrier and bearings from the conventional planetary gearbox structure. The planet gears are no longer supported by a carrier assembly but instead float freely within the gear train, directly meshing with the sun gear and ring gear. This extraction of the carrier and bearing components eliminates the associated complexity and weight while maintaining structural integrity through the gear meshing itself.
Solution Approach 2:
The sun gear and ring gear perform dual functions: they transmit torque and simultaneously provide radial support for the planet gears through their meshing engagement. This eliminates the need for dedicated support structures (carrier and bearings), as the existing gear components assume multiple roles in the system.
2Force
If high reduction ratios are achieved using multi-stage planetary gearboxes, then the output torque is high, but the overall size and weight of the gearbox increases substantially
Solution Approach 1:
The patent implements a nested compound planet structure where two different planet gear sets are combined into a single integrated planet assembly. The first planet gear meshes with the sun gear, and the second planet gear meshes with the ring gear, with both planets rigidly connected. This nested arrangement achieves high reduction ratios in a single stage without requiring multiple separate gearbox stages, thereby reducing overall size and weight.
3Volume of moving object
If standard planetary gearboxes use a small sun gear pinion to limit size, then the gearbox is compact, but the maximum torque that can be generated is limited by the sun gear size
Solution Approach 1:
The patent employs asymmetric planet gear configuration where the two planet gears in the compound structure have different sizes and tooth counts. The first planet gear is optimized for meshing with the sun gear, while the second planet gear is optimized for meshing with the ring gear. This asymmetric design allows each gear to be sized optimally for its specific function, maximizing torque transmission capability while maintaining compact dimensions.
Data Source
AI summary
A planetary gearbox including a first sun gear; a first ring gear; a first set of planet gears meshing with the first sun gear and the first ring gear; a second sun gear; a second ring gear; a second plurality of planet gears meshing with the second ring gear and the second sun gear, wherein the ith gear in the first set of planet gears is fixed to the ith gear in the second set of planet gears so that the gears in the first set and the second set rotate together coaxially. The resulting planetary gearbox can be readily integrated into compact robotic joints. Its few lightweight components can be manufactured with high accuracy with standard machining techniques.