Multistage Planetary Transmission for Compact High-Torque Actuation

The transmission system is divided into multiple planetary gear stages (first stage, second stage, third stage) with different reduction ratios. Each stage handles a portion of the total reduction ratio, distributing the mechanical load across multiple gear meshes rather than concentrating it in a single stage. This segmentation allows the system to achieve high overall reduction ratio (600 or higher) while maintaining acceptable bearing capacity in each individual stage.

The patent employs a multistage planetary gear mechanism that adds a temporal/dimensional dimension to the torque transmission. Instead of achieving high reduction in a single mechanical stage, the system progresses through multiple sequential stages (first, second, third), each contributing to the cumulative reduction ratio. This multi-dimensional approach enables high torque capability while distributing stress across multiple gear interfaces.

The planetary gear mechanism employs a nested structure where planetary gears are arranged within the annular space between the sun gear and the internal gear. The multiple stages are configured to nest within each other, with each subsequent stage utilizing the space efficiently. The planetary gears of each stage are positioned in the radial space between the sun gear and internal gear, maximizing space utilization and reducing the overall volume of the actuator.

By transitioning from a single-stage to a multistage planetary gear system, the patent effectively uses the axial dimension to achieve high reduction ratio. Each planetary gear stage adds a compact axial layer, allowing the system to achieve reduction ratio of 600 or higher without proportionally increasing the radial or lateral dimensions. This dimensional approach enables high torque capability while maintaining a compact actuator size suitable for surgical applications.

In the last planetary gear stage, the patent employs an asymmetric arrangement of four planetary gears instead of a symmetric configuration. The planetary gears are positioned at unequal angular intervals around the sun gear, creating an asymmetric load distribution that balances the radial forces. This asymmetric positioning causes the radial load to cancel out, achieving zero net radial load on the sun gear and internal gear, which reduces wear and improves reliability.

The patent applies different gear arrangement strategies to different stages of the planetary gear mechanism. The first, second, and third stages use conventional symmetric arrangements, while only the last stage employs the asymmetric four-gear configuration. This localized application of asymmetric arrangement targets specifically the stage where radial load reduction provides the greatest benefit, while maintaining simpler manufacturing in other stages.