Fluidic Bladder Pressure Control with Equal-Length Hoses
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Solution Overview
Problem
Existing systems for measuring and regulating pressure in a bladder with a circulating fluid face errors due to fluid density and elevation differences between the bladder and pressure sensor, especially when using denser fluids like water, leading to significant head pressure errors and complications with fluid flow.
Innovation Solution
A pressure measurement and control system that uses a pump, supply and return hoses of equal length to separate the bladder from pressure sensors, with a controller generating error signals based on the difference between setpoint and average pressure measurements from supply and return sensors, and compensates for head pressure by estimating it when the pump is turned off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If water or liquid coolant is used to pressurize the bladder for cooling purposes, then thermal transfer characteristics are improved, but head pressure error increases significantly due to fluid density and elevation difference
Solution Approach 1:
The system uses feedback control by continuously monitoring pressure at both supply and return lines and adjusting pump operation to maintain accurate bladder pressure control despite head pressure variations. The controller compares measured pressures against desired setpoints and modifies pump output accordingly.
Solution Approach 2:
The system changes the measurement approach by taking the average of supply and return pressure measurements to compensate for head pressure effects. This parameter change in the measurement method allows accurate bladder pressure determination even when using dense liquid coolants with significant elevation differences.
2Ease of operation
If the pressure sensor is located remotely from the bladder, then system flexibility and ease of operation are improved, but measurement accuracy deteriorates due to head pressure and turbulent flow effects
Solution Approach 1:
Remote pressure sensing is enabled through feedback control that uses both supply and return line pressure measurements. The system compensates for line losses and head pressure by continuously adjusting based on the difference between measured pressures and desired bladder pressure, allowing accurate remote monitoring without requiring sensors at the bladder location.
Solution Approach 2:
The system uses the return line as an intermediary measurement point that, when combined with supply line measurements, provides accurate bladder pressure information. The return pressure sensor acts as a mediator that helps compensate for the effects of remote sensing and turbulent flow in the supply line.
3Ease of manufacture
If supply and return fluid lines are made equal in length and diameter, then system complexity is reduced and manufacturing is simplified, but pressure measurement accuracy is compromised due to turbulent flow pressure drops
Solution Approach 1:
The system compensates for pressure drops in equal-length supply and return lines through feedback control. By monitoring both pressures and comparing their difference against expected values, the system can accurately determine bladder pressure even when line configurations are simplified and turbulent flow causes pressure losses.
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
This system accurately measures and regulates bladder pressure by compensating for head pressure errors, ensuring that the pressure setpoint is achieved regardless of elevation differences, even with turbulent fluid flow, and maintains flexibility in cuff design and operation.
Implementation Method 1
a pump coupled to a reservoir, a first fluid line coupled from the pump to supply pressurized fluid to a cuff bladder, the cuff bladder having a return line returning the circulated fluid to the reservoir
Implementation Method 2
when the objective of the bladder is also cooling of an encircled limb, water or other liquid with greater density and greater thermal transfer characteristics may be used
Implementation Method 3
A first error is an offset error associated with the fluid density and elevation difference between the bladder and pressure sensor. When water is used as a coolant, the added fluid pressure from the elevation difference between the fluid and pressure sensor measurement point, known as 'head pressure,' increases to 9.8 Pa per mm of head height
Implementation Method 4
the pressure measured by taking the average of the supply pressure sensor measurement and return pressure sensor measurement
Data Source
AI summary
A process for a therapeutic bladder pressure estimator is operative with a pump connected, in sequence, to a first hose, a supply pressure sensor, a second hose, a bladder having an inlet coupled to the second hose, a bladder outlet coupled to a third hose of substantially equal length to the second hose, a return pressure sensor, and a fourth hose coupled to the return pressure sensor and returning fluid from the pump to the reservoir. The process forms an error signal from the difference between a setpoint and the average of the supply and return pressures. A head pressure measurement may be done by turning the pump off after a steady state reading is made.