Linear back-drive differentials have been proposed as alternatives to conventional gear differentials for applications in which there is only limited rotational motion (e.g., oscillation). The finite nature of the rotation makes it possible to optimize a linear back-drive differential in ways that would not be possible for gear differentials or other differentials that are required to be capable of unlimited rotation. As a result, relative to gear differentials, linear back-drive differentials could be more compact and less massive, could contain fewer complex parts, and could be less sensitive to variations in the viscosities of lubricants.
Linear back-drive differentials would operate according to established principles of power ball screws and linear-motion drives, but would utilize these principles in an innovative way. One major characteristic of such mechanisms that would be exploited in linear back-drive differentials is the possibility of designing them to drive or back-drive with similar efficiency and energy input: in other words, such a mechanism can be designed so that a rotating screw can drive a nut linearly or the linear motion of the nut can cause the screw to rotate.
A linear back-drive differential (see figure) would include two collinear shafts connected to two parts that are intended to engage in limited opposing rotations. The linear back-drive differential would also include a nut that would be free to translate along its axis but not to rotate. The inner surface of the nut would be right-hand threaded at one end and left-hand threaded at the opposite end to engage corresponding right- and left-handed threads on the shafts. A rotation and torque introduced into the system via one shaft would drive the nut in linear motion. The nut, in turn, would back-drive the other shaft, creating a reaction torque. Balls would reduce friction, making it possible for the shaft/nut coupling on each side to operate with 90 percent efficiency.
This work was done by Peter Waydo of Caltech for NASA's Jet Propulsion Laboratory.
NPO-30366
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Linear Back-Drive Diiferentials
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Overview
This document presents a technical overview of a novel suspension system designed for mobile robots, particularly those used in exploration, such as NASA's rovers. The focus is on the Linear Backdrive Differential, which addresses the limitations of traditional gear-based differentials used in rocker-bogie suspension systems. These conventional systems often face issues related to mass, complexity, and reliability, especially under high loads and oscillating motions.
The Linear Backdrive Differential operates on principles of power screws and linear motion devices, offering a more compact and efficient solution tailored for oscillating motion. Unlike traditional gear differentials, which are bulky and complex, this new design minimizes the number of moving parts, enhancing reliability and reducing sensitivity to lubrication issues. The system utilizes a large-lead ball screw assembly that allows for both driving and backdriving, effectively converting rotational motion into linear motion and vice versa. This mechanism significantly reduces friction losses, achieving up to 90% efficiency per side.
The document outlines the advantages of this innovative differential over existing methods, such as gear differentials and rocker linkage differentials. The Linear Backdrive Differential is less massive, simpler, and more reliable, making it suitable for the unique demands of mobile robotic applications. It is particularly beneficial in environments where space is limited, as it requires less room for operation compared to traditional systems.
Additionally, the document highlights the potential applications of robots equipped with hopping and wheeled locomotion capabilities. These robots can be utilized in diverse fields, including agriculture, search-and-rescue operations, military tasks, landmine removal, law enforcement, and scientific exploration on Earth and other planets.
Overall, the document emphasizes the innovative nature of the Linear Backdrive Differential and its potential to enhance the performance and reliability of mobile robots, paving the way for advancements in robotic exploration and various practical applications. The work is conducted under the auspices of NASA and the Jet Propulsion Laboratory, showcasing the commitment to developing cutting-edge technology for future exploration missions.
