Exoskeleton Actuator Structure for Misaligned Load Back Drive
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Solution Overview
Problem
Existing linear actuators face issues with back drive and lack of flexibility due to misaligned loads, particularly when converting rotary motion to linear motion, as they do not allow for bi-directionality and efficient force application off-axis from the screw axis, limiting their use in compact applications.
Innovation Solution
A linear actuation device with a threaded shaft and a movable element constrained by guiding rods and ball joints, allowing rotation to translate linearly while preventing transverse moments and enabling force application misaligned with the shaft, ensuring continuous operation and bi-directionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a screw-nut assembly is used for converting rotary motion to linear motion, then the actuator can achieve compact dimensions, but it cannot handle misaligned loads without back drive problems
Solution Approach 1:
The patent introduces a movable element with a cavity that receives the threaded shaft, acting as an intermediary between the screw mechanism and the load. This movable element can translate along the shaft axis while accommodating misaligned forces, preventing direct transmission of transverse moments to the screw-nut assembly and eliminating back drive issues while maintaining compact dimensions
2Device complexity
If the nut screw is rigidly connected to the load component, then the structure is simplified, but misaligned loads cause binding and loss of reversibility
Solution Approach 1:
The patent employs two guiding rods that are movable relative to the movable element, constrained only in the axial direction. This dynamic arrangement allows the guiding rods to automatically adjust and accommodate misaligned loads, enabling the actuator to handle off-axis forces without binding while maintaining simple structure and full reversibility
3Reliability
If linear rails are added to constrain the nut screw, then misalignment problems are reduced, but the actuator still cannot eliminate back drive issues and complexity increases
Solution Approach 1:
The patent divides the movable element into first and second elements constrained with each other, where the first element couples to the threaded shaft and the second element couples to the guiding rods. This segmentation allows independent optimization of each component's function, achieving reliable alignment stability through the guiding rods while keeping the overall structure simpler than traditional linear rail solutions
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 solution enhances back drive operation and flexibility, allowing for compact and reversible actuation with continuous translation and reduced binding, enabling applications with misaligned force application and minimizing overall dimensions.
Implementation Method 1
a threaded shaft (2) connected at one end to driving means intended to allow the threaded shaft to rotate about its longitudinal axis, and a movable element (3) provided with a cylindrical cavity, intended to receive the threaded shaft, and configured such that a rotation of the threaded shaft corresponds to a translation of the movable element along the longitudinal axis
Implementation Method 2
two guiding rods (4, 4') coupled to the movable element and constraining the translation thereof along a direction parallel to the longitudinal axis
Implementation Method 3
the portion and the seat are shaped such that the contact between the seat and the portion occurs in a contact area within a plane comprising the longitudinal axis and it is parallel to the plane comprising the development axes of the two guiding rods
Data Source
Figure 1~2
Figure 3~4c
Figure 5~6
AI summary
The present invention relates to an actuation device (1) comprising a threaded shaft (2) connected at one end to driving means adapted to allow the threaded shaft (2) to rotate about its longitudinal axis (a). The device further comprises a movable element (3) provided with a cylindrical cavity (30) adapted to receive the threaded shaft (2), and configured in such a way that a rotation of the threaded shaft (2) corresponds to a translation the movable element (3) along the longitudinal axis (a). The device (1) further comprises two guiding rods (4, 4') coupled to the movable element (3) and adapted to constrain the translation of the latter along a direction parallel to the longitudinal axis (a). The movable element (3) comprises a first (31) and a second (32) element constrained to each other, wherein the first element (31) is coupled to the threaded shaft (2) and the second element (32) is coupled to the two guiding rods (4, 4'). A portion (320) protrudes from the second element (32) adapted to fit into a seat (312) formed in the first element (31), and wherein the portion (320) and the seat (312) are shaped in such a way that the contact between the seat (312) and the portion (320) takes place in a contact zone that extends along a section of the portion (320) whose midpoint lies in a plane that comprises the longitudinal axis (a) and is parallel to the plane which comprises the development axes (β,β ') of the two guiding rods (4, 4').