Everting Sheath Reel Torque Control for Predictable Deployment
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Solution Overview
Problem
Everting sheaths, or everting tube robots, face challenges in controlling their growth rate and estimating the position of the leading tip during expansion due to nonlinear material properties, leading to unpredictable deployment and potential trauma in sensitive environments.
Innovation Solution
A system with a rotatable reel and torque mechanism, such as a brake mechanism or eddy current brake, applies passive torque to control the release rate of the sheath from the reel, enhancing control over the eversion process and enabling accurate estimation of the leading tip position without additional sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If fluid pressure is increased to expand the everting sheath, then the sheath extends to longer lengths, but the growth rate becomes unpredictable and may decrease or stop until a certain pressure is attained
Solution Approach 1:
The patent employs feedback control by sensing the actual growth rate of the everting sheath and adjusting the fluid pressure accordingly. Sensors monitor the position of the leading tip and this information is fed back to a controller that modulates the pressure to maintain a desired constant growth rate, resolving the unpredictability issue
Solution Approach 2:
The patent dynamically changes the fluid pressure parameter based on the observed growth behavior. When the growth rate decreases or stops, the controller increases pressure; when the growth rate is appropriate, pressure is maintained or reduced. This dynamic parameter adjustment ensures reliable and predictable extension
2Length of moving object
If fluid pressure is increased to expand the everting sheath, then the sheath extends to longer lengths, but the sheath may explosively deploy at an uncontrolled high speed
Solution Approach 1:
The feedback control system continuously monitors the growth speed and adjusts pressure in real-time to prevent explosive deployment. When the sheath approaches a certain length or speed threshold, the controller reduces pressure to maintain controlled expansion, preventing uncontrolled high-speed deployment
Solution Approach 2:
The patent applies preliminary anti-action by using the torque mechanism to counteract the fluid pressure before explosive deployment can occur. The torque mechanism creates a balancing force that prevents the sheath from accelerating uncontrollably, especially as the sheath extends to longer lengths where pressure buildup could lead to explosive deployment
3Ease of operation
If conventional everting sheath design is used, then passive self-navigation is achieved, but control over growth rate and leading tip position is lost
Solution Approach 1:
The patent introduces a reel as an intermediary mechanism between the fluid pressure source and the everting sheath. The reel provides mechanical advantage and controlled release, allowing the operator to regulate the eversion process while maintaining the passive self-navigation benefit of the original design
Solution Approach 2:
The patent replaces direct fluid pressure control with a mechanical reel-based control system. Instead of relying solely on fluid pressure to drive eversion, the reel mechanism provides precise mechanical control over the release rate, enabling accurate positioning without sacrificing the passive navigation capability
4Strength
If inelastic materials are used for the sheath, then deformation under load is facilitated, but nonlinear material properties make modeling and control challenging
Solution Approach 1:
The feedback control system compensates for the nonlinear material behavior by continuously sensing the actual position and growth rate, then adjusting pressure in real-time. This closed-loop approach eliminates the need for complex predictive modeling of the nonlinear inelastic material properties
Solution Approach 2:
The everting sheath material serves itself by utilizing its inherent nonlinear deformation characteristics under fluid pressure. The material's ability to deform and creep under load is harnessed rather than fought against, with the control system adapting to the material's natural behavior rather than requiring the material to conform to linear elastic models
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 system provides predictable and controlled eversion, minimizing trauma to surrounding tissues by ensuring smooth expansion and accurate tip positioning, particularly useful in medical applications.
Implementation Method 1
a torque mechanism operable to apply a passive torque (such as a brake mechanism, a centrifugal clutch, an eddy current brake, a passive motor, or other suitable passive torque mechanisms) to the reel
Implementation Method 2
an eddy current brake
Implementation Method 3
a centrifugal clutch
Implementation Method 4
a torque mechanism operable to apply a passive torque (such as a brake mechanism, a centrifugal clutch, an eddy current brake, a passive motor, or other suitable passive torque mechanisms) to the reel (such as via the axle or other component that drives the reel) to adjust a rate at which the sheath is released from the reel as the sheath everts from the retracted position to the extended position
Data Source
AI summary
Apparatuses, systems, and methods are disclosed for regulating an eversion process in everting sheath systems to avoid uncontrolled deployment of the sheath. The sheath system includes a reel and a sheath stored thereon, where the sheath is capable of everting from a retracted position to an extended position as the reel rotates about a rotational axis. The rotational characteristics of the reel are controlled by a torque mechanism operable to directly or indirectly apply a passive torque to the reel to adjust a rate at which the sheath is released from the reel as the sheath everts from the retracted position to the extended position.