Levitated Impeller Startup Sequence for Centrifugal Pump
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Centrifugal pumps with magnetically levitated impellers face excessive wear during startup due to unbalanced axial forces and high normal forces between the impeller and the housing before levitation is achieved, leading to mechanical damage and potential blood clot formation.
Innovation Solution
A centrifugal pump system with a disc-shaped impeller and a controller that uses a commutator circuit and sensing circuit to determine phase voltages, employing a pseudo impeller phase and gradually increasing magnetic field to minimize mechanical wear by ramping up phase voltage commands and accelerating rotation, avoiding the need for a strong stationary magnetic field during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a strong stationary magnetic field is used to align the impeller during startup, then the impeller can be quickly positioned, but excessive mechanical wear occurs due to high normal forces and rubbing against the housing
Solution Approach 1:
The system performs preliminary positioning of the impeller using a weak stationary magnetic field before applying the rotating magnetic field. This preliminary action orients the impeller in a known direction without generating high normal forces that cause wear, thus preparing the system for subsequent rotation while avoiding the harmful rubbing that occurs with strong field alignment
Solution Approach 2:
The patent transitions from a static strong magnetic field alignment method to a dynamic rotating magnetic field method. The rotating field gradually accelerates the impeller from rest, maintaining lower normal forces throughout the acceleration process compared to the instantaneous strong field alignment, thereby reducing mechanical wear while achieving the desired rotational speed
2Productivity
If the impeller is accelerated quickly to levitation speed, then productivity is improved, but mechanical wear increases due to high normal forces before separation
Solution Approach 1:
The system uses a rotating magnetic field that gradually accelerates the impeller from rest to levitation speed. This dynamic acceleration process maintains lower normal forces between the impeller and housing compared to instantaneous high-speed engagement, reducing mechanical wear while achieving quick startup through controlled rotational acceleration
Solution Approach 2:
The patent changes the parameters of the magnetic field over time during startup - specifically, the rotating magnetic field's strength and frequency are gradually increased to accelerate the impeller. This parameter change approach allows rapid acceleration to levitation speed while controlling the normal forces to minimize wear during the transition period
3Device complexity
If the impeller rests against chamber walls due to unbalanced axial forces, then the magnetic bearing structure is simplified, but mechanical wear and potential blood clot formation increase
Solution Approach 1:
The patent replaces the mechanical bearing system with a magnetic bearing system that uses a rotating magnetic field to levitate the impeller. This substitution eliminates direct mechanical contact between the impeller and chamber walls, preventing wear and thrombus formation while maintaining structural simplicity through the use of electromagnetic forces alone
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
Reduces mechanical wear and prevents blood clot formation by gradually aligning and rotating the impeller, ensuring it levitates without initial contact with the housing, thus maintaining the impeller's integrity and reducing the risk of mechanical damage.
Implementation Method 1
A multiphase magnetic stator is disposed at a second end of the pump housing for generating a rotating magnetic field for axially and rotationally attracting the second magnetic structure
Implementation Method 2
A levitation magnetic structure is disposed at a first end of the pump housing having a levitating magnetic field for axially attracting the first magnetic structure
Implementation Method 3
A controller is suitable to calculate successive commanded values for the phase voltages during a running state in response to a desired impeller speed and an actual impeller phase
Data Source
Figure 1~3
Figure 2
Figure 4
AI summary
A centrifugal pump system having an impeller rotating with first and second magnetic structures on opposite surfaces. A levitation magnetic structure is disposed at a ftrst end of a pump housing having a levitating magnetic field for axially attracting the first magnetic structure. A multiphase magnetic stator at a second end of the pump housing generates a rotating magnetic field for axially and rotationally attracting the second magnetic structure. A commutator circuit provides a plurality of phase voltages to the stator. A sensing circuit determines respective phase currents. A controller calculates successive commanded values for the phase voltages during a running state in response to a desired impeller speed and an actual impeller phase. The controller has a startup interval during which the commanded values of the phase voltages are determined in response to a pseudo impeller phase and in response to a ramping gain factor.