Constant Force Spring Hydraulic Actuator Design
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Solution Overview
Problem
Existing hydraulic actuators with fail-safe retraction features require large springs, increasing the actuator's length, which is a concern in applications where space is limited, and these springs are not adequately protected from harsh environments.
Innovation Solution
The use of constant force retraction springs packaged within a hydraulic fluid cavity to provide fail-safe retraction while minimizing the actuator's length and protecting the springs from contaminants like seawater and sand, along with an optional sensor to detect the piston's linear position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard fail-safe springs (coil or wave springs) are used for retraction, then fail-safe retraction functionality is achieved, but the actuator length increases significantly to accommodate spring travel and solid height
Solution Approach 1:
The patent changes the fundamental parameter of spring force characteristics from variable force (standard coil/wave springs) to constant force (progressive unwinding rolled ribbon springs). This parameter change allows the spring to maintain a compact form factor while providing sufficient retraction force throughout its entire travel range, resolving the contradiction between reliability and length.
Solution Approach 2:
The patent transitions from using traditional three-dimensional coil or wave spring geometries to a two-dimensional rolled ribbon spring configuration. This dimensional change enables the spring to be packaged in a much smaller volume while maintaining the necessary travel distance and force characteristics, directly addressing the length constraint.
2Length of moving object
If constant force retraction springs are used, then actuator length is minimized, but the springs are exposed to harsh environments (seawater, sand, contaminants)
Solution Approach 1:
The patent places the constant force retraction spring inside the hydraulic fluid cavity, nesting the spring within the existing actuator structure. This nested configuration provides natural protection from environmental contaminants while the hydraulic fluid acts as an additional barrier, resolving the contradiction between compact design and environmental protection.
Solution Approach 2:
The hydraulic fluid cavity serves as an intermediary barrier between the constant force spring and the harsh external environment. The cavity walls and hydraulic fluid protect the spring from seawater, sand, and contaminants while allowing the spring to function normally, thus resolving the contradiction between minimizing length and protecting from harmful factors.
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 allows for a compact hydraulic actuator design that maintains fail-safe functionality even in harsh environments, ensuring reliable retraction without the length constraints of traditional springs and providing environmental protection for the spring mechanisms.
Implementation Method 1
The constant force retraction spring(s) described herein can be any constant force spring construction in which the force it exerts over its range of motion is constant.
Implementation Method 2
The hydraulic fluid cavity is in fluid communication with the piston chamber to allow passage of hydraulic fluid between the hydraulic fluid cavity and the piston chamber.
Data Source
AI summary
A fail-safe hydraulic actuator that uses one or more constant force retraction springs to provide fail-safe retraction of the piston and piston rod in the event of loss of hydraulic pressure. The constant force retraction spring(s) can be packaged in a small volume thus decreasing the overall length of the actuator. This allows the actuator to be utilized in areas where length is a concern. The constant force retraction spring(s) are part of constant force retraction spring mechanism(s) that can be mounted within a hydraulic fluid cavity of the fail-safe hydraulic actuator to protect the constant force retraction spring mechanism(s) from the environment surrounding the actuator. A sensor that detects the linear position of the piston within the piston chamber may also be provided.