U.S. patent application number 13/793937 was filed with the patent office on 2013-09-26 for method and apparatus for sensing of levitated rotor position.
This patent application is currently assigned to World Heart Corporation. The applicant listed for this patent is WORLD HEART CORPORATION. Invention is credited to Gill Beamson, Carl C. Ketcham.
Application Number | 20130251502 13/793937 |
Document ID | / |
Family ID | 48014304 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130251502 |
Kind Code |
A1 |
Ketcham; Carl C. ; et
al. |
September 26, 2013 |
Method and Apparatus for Sensing of Levitated Rotor Position
Abstract
A pump with magnetically-levitated rotor includes a position
sensor having an eddy-current sensor coil that operates as a
resonating element in a low frequency oscillator located within the
pump housing. The oscillator is operably interconnected with
additional electronics that shift the frequency of the oscillator
output signal to a lower frequency. The lower frequency signal is
directed to a frequency measurement circuit that provides a value
representing a position of the rotor.
Inventors: |
Ketcham; Carl C.; (Murray,
UT) ; Beamson; Gill; (Salt Lake City, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
WORLD HEART CORPORATION |
Salt Lake City |
UT |
US |
|
|
Assignee: |
World Heart Corporation
Salt Lake City
UT
|
Family ID: |
48014304 |
Appl. No.: |
13/793937 |
Filed: |
March 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61613307 |
Mar 20, 2012 |
|
|
|
Current U.S.
Class: |
415/1 ;
415/118 |
Current CPC
Class: |
F04D 29/048 20130101;
F04D 15/0088 20130101; F04D 29/049 20130101; F04D 15/00 20130101;
F04D 29/058 20130101 |
Class at
Publication: |
415/1 ;
415/118 |
International
Class: |
F04D 15/00 20060101
F04D015/00 |
Claims
1. A pump system configured to provide fluid flow, comprising: a
stator housing having an inlet and an outlet and a fluid pathway; a
rotor disposed within the fluid pathway between the inlet and the
outlet, the rotor hub comprising a body having a leading portion
positioned adjacent the inlet, a trailing portion positioned
adjacent the outlet; an eddy current sensor coil positioned
external the fluid pathway and operable to determine a position of
the rotor hub relative to the stator housing, the sensor coil
operating as a resonating element in a low-frequency
oscillator.
2. The pump system of claim 1, further comprising a frequency
shifting device that shifts a frequency of an output signal from
the oscillator to a lower frequency signal.
3. The pump system of claim 2, further comprising a frequency
measurement circuit that measures the frequency of the lower
frequency signal and outputs a value representative of a position
of the rotor hub relative to the stator housing.
4. The pump system of claim 3, wherein the value output from the
frequency measurement circuit is in the form of a binary number, an
electrical current, or an electrical voltage.
5. The pump system of claim 1, further comprising a phase-locked
loop that locks a phase of an output from the oscillator.
6. The pump system of claim 1, further comprising a
frequency-locked loop that locks a frequency of an output from the
oscillator.
7. The pump system of claim 1, further comprising a memory element
containing at least one of calibration, characterization and
correction parameters for the sensor coil.
8. The pump system of claim 2, further comprising a high speed
counter configured to measure an interval of time between cycles of
the lower frequency signal.
9. The pump system of claim 2, further comprising a high speed
counter configured to measure a number of cycles of the lower
frequency signal over a specified time interval.
10. The pump system of claim 1, further comprising a pump housing,
the stator housing, the rotor hub, and the sensor coil are
positioned in the pump housing.
11. The pump system of claim 10, further comprising a
microprocessor positioned remote from the pump housing.
12. The pump system of claim 1, further comprising at least one
permanent magnet bearing and a magnet motor, the magnet motor
comprising a motor magnet carried by the rotor hub and a motor coil
carried by the stator housing, the at least one permanent magnet
bearing levitating the rotor hub within the stator housing, and the
magnet motor operable to rotate the rotor hub within the stator
housing.
13. A sensor assembly for a pump with magnetically-levitating
rotor, the sensor assembly comprising: a sensor coil positioned on
a stator of the pump; a rotor of the pump arranged within the
stator and having a conductive surface; a low frequency oscillator
positioned within a housing of the pump; wherein the sensor coil
operates as a resonating element in the low frequency oscillator in
response to a change in relative position between the rotor and
sensor coil, and an output signal from the low frequency oscillator
is used to adjust a position of the rotor relative to the
stator.
14. The sensor assembly of claim 13, wherein an output of the low
frequency oscillator is in the range of about 200 kHz to about 350
kHz.
15. The sensor assembly of claim 14, wherein an output of the low
frequency oscillator is a sine wave signal.
16. An active magnetically levitating pump system configured to
provide fluid flow, comprising: a stator housing having a fluid
pathway; a rotor disposed within the fluid pathway; an eddy current
sensor coil positioned external the fluid pathway and operable to
determine a position of the rotor with respect to a defined axis of
the stator housing, the sensor coil operating as a resonating
element in a low-frequency oscillator.
17. The active magnetically levitating pump system of claim 16,
wherein the eddy current sensor coil is operable to determine a
position of the rotor with respect to a longitudinal axis of the
stator housing.
18. The active magnetically levitating pump system of claim 16,
wherein the eddy current sensor coil is operable to determine a
position of the rotor with respect to a lateral axis of the stator
housing.
19. The active magnetically levitating pump system of claim 16,
further comprising a pump housing, the stator housing, rotor and
eddy current sensor coil being positioned in the pump housing.
20. The active magnetically levitating pump system of claim 16,
wherein the low-frequency oscillator is positioned in the pump
housing.
21. A method of determining a rotor position in a stator housing,
the method comprising: providing a stator housing having a fluid
pathway, a rotor hub positioned in the fluid pathway, a sensor coil
positioned external the fluid pathway, and an oscillator; inducing
eddy currents in the rotor hub via the magnetic field of the sensor
coil, which eddy currents in turn produce magnetic fields that
interact with the magnetic fields of the sensor coil as the rotor
hub is moved relative to the stator housing; determining a position
of the rotor hub relative to the stator housing using an output of
the oscillator.
22. The method of claim 21, further comprising shifting a frequency
of a signal output from the oscillator to create a lower frequency
signal, measuring the lower frequency signal, and providing a
correction value for the measured lower frequency signal, the
correction value representing a position of the rotor hub relative
to the stator housing.
23. The method of claim 21, further comprising locking a phase of a
signal output from the oscillator to create a phase locked signal,
measuring the phase locked signal, and providing a correction value
for the measured phase locked signal, the correction value
representing a position of the rotor hub relative to the stator
housing.
24. The method of claim 21, further comprising locking a frequency
of a signal output from the oscillator to create a frequency locked
signal, measuring the frequency locked signal, and providing a
correction value for the measured frequency locked signal, the
correction value representing a position of the rotor hub relative
to the stator housing.
25. The method of claim 21, further comprising
magnetically-levitating the rotor hub in the fluid pathway, and
controlling a longitudinal position of the rotor hub relative to
the stator housing in response to the determined position of the
rotor hub.
26. A method of determining a position of a rotor within a housing
in a pump with magnetically-levitating rotor system, the method
comprising: providing a controller and a pump, the pump having a
rotor, a stator, a position sensor, and an oscillator, the rotor
being positioned inside the stator, the position sensor being
positioned on the stator, and the position sensor comprising a
coil; creating a change in frequency in the oscillator with the
position sensor in response to a change in position of the rotor
relative to the stator; processing an output signal of the
oscillator with the controller to create a correction value
representative of the change in relative axial position; correcting
a position of the rotor based on the value.
27. The method of claim 26, further comprising correcting the
position of the rotor with a voice coil.
28. The method of claim 26, further comprising providing a
controller that is positioned remote from the oscillator, the
controller comprising a microprocessor configured to determine the
correction value using the output signal of the oscillator.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/613,307, filed Mar. 20, 2012, entitled
"Method and Apparatus for Sensing of Levitated Rotor Position,"
which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates generally to position
sensors, and more specifically relates to position sensors for
magnetically-levitating pumps, such as cardiac assist pumps that
may be implanted in a patient.
BACKGROUND OF THE INVENTION
[0003] Rotor dynamic pumps, such as centrifugal, mixed-flow, and
axial-flow pumps with mechanical bearings or magnetically suspended
systems, have been widely used as a ventricular assist device to
support patients with heart diseases. In magnetically-levitated
blood pumps, which generally include an impeller or rotor that is
both magnetically suspended and rotated without mechanical means,
the magnetic bearings may be used to constrain motion in a
longitudinal direction and active elements may be used to control a
lateral position of the rotor. There is a relatively narrow region
of travel along the longitudinal axis over which this constraint
applied by the magnetic bearings occurs, and over which there is an
adequate force to maintain the concentricity of the rotating
element (e.g., rotor) with the longitudinal axis. The magnetic
bearing forces tend to push the rotor longitudinally away from this
narrow functional region. A control system is used to sense the
longitudinal position of the rotor, and based on this position,
apply a force to counter the travel away from the intended location
and maintain the rotor in the desired longitudinal position.
[0004] For magnetically-levitated pumps, it has historically been a
difficult problem to determine the rotor's longitudinal position
with suitable precision and with a sufficient bandwidth to maintain
a stable position along the longitudinal axis. This difficulty is
due, at least in part, to the sealed nature of the fluid flow path
through the stator. In particular, in blood pumps, titanium alloys
are used for compatibility with the blood. The use of titanium
requires that the rotor position sensor be able to sense the
position of the rotor through at least one layer of titanium.
[0005] Existing control systems that attempt to address these
problems related to magnetically-levitated pumps have suffered from
a number of shortcomings. For example, such systems are sensitive
to external electrical noise such as radio signals, changing
magnetic fields within the pump, temperature changes in the pump,
temperature changes in the controller, and temperature changes in
the cable that connects the pump to the controller. These systems
also have limitations related to minimizing a size of the pump
housing because of the large number and size of the electronics
that are typically required to be positioned inside the pump
housing. The sensitivity to changes in cable impedance is also
problematic due to fluid ingress, flexure or other reasons.
SUMMARY OF THE INVENTION
[0006] Various embodiments of position sensors for
magnetically-levitated pumps are set forth herein in accordance
with the present disclosure.
[0007] In accordance with one embodiment of the present disclosure,
a magnetically-levitated pump includes a position sensor having an
eddy-current sensor coil that operates as a resonating element in a
low frequency oscillator located within the pump housing. The
oscillator is operably interconnected with additional electronics
that shift the frequency of the oscillator output signal to a lower
frequency. The lower frequency signal is directed to a frequency
measurement circuit that provides a value representing a position
of the rotor along the longitudinal axis of the pump. The value may
be in the form of, for example, a binary number, an electrical
circuit, an electrical voltage, or other representation.
[0008] An alternative position sensor includes an eddy-current
sensor coil that operates as a resonating element in a low
frequency oscillator that is positioned within the pump housing. An
output from the oscillator may be operably connected with the input
to a phase locked loop or frequency locked loop. The output of the
phase locked loop or frequency locked loop may be a feedback value
that represents a position of the rotor along the longitudinal axis
of the pump. The feedback value may be in the form of, for example,
a binary number, an electrical current, an electrical voltage, or
other representation.
[0009] Either of the example position sensors described above may
be associated with at least one memory element that stores
calibration, characterization, correction, and other parameters for
the pump or the controller. The parameters may permit the pump to
be operably interchanged with any similar pump. For example, a
common controller positioned remotely of the pump housing may be
used with any of a number of different pumps because each pump
separately carries a number of the parameters stored in memory that
are accessible by the controller. Similarly, any given pump may be
used with a plurality of different controllers because of
parameters of the controller that are stored by the controller.
[0010] The frequency measurements in the example circuitry
described herein may include a high speed counter that is
configured to measure an interval of time between cycles of the low
frequency signal. The number of cycles of the low frequency signal
may be measured over a specified time interval. A microprocessor of
the pump system may include such a timer/counter subsystem.
[0011] Another aspect of the present disclosure relates to a pump
system configured to provide fluid flow and that includes a stator
housing, a rotor hub, and an eddy current sensor coil. The stator
housing has an inlet, an outlet and a fluid pathway. The rotor hub
is disposed within the fluid pathway between the inlet and the
outlet, and includes a body having a leading portion positioned
adjacent the inlet and a trailing portion positioned adjacent the
outlet. The eddy current sensor coil is positioned external the
fluid pathway and operable to determine a position of the rotor hub
relative to the stator housing. The sensor coil operates as a
resonating element in a low-frequency oscillator.
[0012] The pump system may include a frequency shifting device that
shifts a frequency of an output signal from the oscillator to a
lower frequency signal. The pump system may include a frequency
measurement circuit that measures the frequency of the lower
frequency signal and outputs a value representative of a position
of the rotor hub relative to the stator housing. The value that is
output from the frequency measurement circuit may be in the form of
a binary number, an electrical current, or an electrical voltage.
The pump system may include a phase-locked loop that locks a phase
of an output from the oscillator. The pump system may include a
frequency-locked loop that locks a frequency of an output from the
oscillator. The pump system may include a memory element containing
at least one of calibration, characterization, and correction
parameters for the sensor coil.
[0013] The pump system may include a high speed counter configured
to measure an interval of time between cycles of the lower
frequency signal. The pump system may include a high speed counter
configured to measure a number of cycles of the lower frequency
signal over a specified time interval. The pump system may include
a pump housing, wherein the stator housing, rotor hub, and sensor
coil are positioned within the pump housing. The pump system may
include a microprocessor positioned remote from the pump housing.
The pump system may include a permanent magnet bearing and a magnet
motor, wherein the magnet motor includes a motor magnet carried by
the rotor hub and a motor coil carried by the stator housing. The
at least one permanent magnet bearing levitates the rotor hub
within the stator housing, and the magnet motor is operable to
rotate the rotor hub within the stator housing.
[0014] Another aspect of the present disclosure relates to a sensor
assembly for a pump with a magnetically-levitating rotor. The
sensor assembly includes a sensor coil positioned on a stator of
the pump, a rotor of the pump that is arranged within the stator
and having a conductive surface, and a low frequency oscillator
positioned within a housing of the pump. The sensor coil may
operate as a resonating element in the low frequency oscillator in
response to a change in relative position between the conductive
surface and sensor coil. An output signal from the low frequency
oscillator is used to adjust a position of the rotor relative to
the stator. An output of the low frequency oscillator may be in the
range of about 200 kHz to about 350 kHz. An output of the low
frequency oscillator may be a sine wave signal.
[0015] Another aspect of the present disclosure relates to an
active magnetically levitating pump system configured to provide
fluid flow. The pump system includes a stator housing having a
fluid pathway, a rotor disposed within the fluid pathway, and an
eddy current sensor coil. The eddy current sensor coil is
positioned external the fluid pathway and operable to determine a
position of the rotor with respect to a defined axis of the stator
housing. The sensor coil operates as a resonating element in a
low-frequency oscillator.
[0016] The eddy current sensor coil may be operable to determine a
position of the rotor with respect to a longitudinal axis of the
stator housing. The eddy current sensor coil may be operable to
determine a position of the rotor with respect to a lateral axis of
the stator housing. The pump system may include a pump housing,
wherein the stator housing, rotor and eddy current sensor coil are
positioned in the pump housing. The low-frequency oscillator may be
positioned in the pump housing.
[0017] A further aspect of the present disclosure relates to a
method of determining a rotor position in a stator housing. The
method includes providing a stator housing having a fluid pathway,
a rotor hub positioned in the fluid pathway, a sensor coil
positioned external the fluid pathway, and an oscillator. The
method further includes inducing eddy currents in the rotor hub via
the magnetic field of the sensor coil, which eddy currents in turn
produce magnetic fields that interact with the magnetic fields of
the sensor coil as the rotor hub is moved relative to the stator
housing, wherein the sensor coil operates as a resonating element
in the oscillator. The method also includes determining a position
of the rotor hub relative to the stator housing using an output of
the oscillator.
[0018] The method may include shifting a frequency of a signal that
is output from the oscillator to create a lower frequency signal,
measuring the lower frequency signal, and providing a value for the
measured lower frequency signal that represents a position of the
rotor hub relative to the stator housing. The method may include
locking a phase of a signal output from the oscillator to create a
phase locked signal, measuring the phase locked signal, and
providing a value for the measured phase locked signal that
represents a position of the rotor hub relative to the stator
housing. The method may include locking a frequency of a signal
output from the oscillator to create a frequency locked signal,
measuring the frequency locked signal, and providing a value for
the measured frequency locked signal that represents a position of
the rotor hub relative to the stator housing. The method may
include magnetically-levitating the rotor hub in the fluid pathway,
and controlling a longitudinal position of the rotor hub relative
to the stator housing in response to the determined position of the
rotor hub.
[0019] Another example method in accordance with the present
disclosure relates to determining a position of a rotor within a
housing in a magnetically-levitating pump system. The method
includes providing a controller and a pump, wherein the pump
includes a rotor, a stator, a position sensor, and an oscillator,
the rotor is positioned in the stator, the position sensor is
positioned outside of the stator. The position sensor includes a
coil. The method includes creating a change in frequency in the
oscillator with the position sensor in response to a change in
position of the rotor relative to the stator, processing an output
signal of the oscillator with the controller to create a correction
or error value representative of the change in relative axial
position, and correcting a position of the rotor based on the
value.
[0020] The method may also include correcting the position of the
rotor with a voice coil. The method may include providing a
controller that is positioned remote from the oscillator and
includes a microprocessor configured to determine the correction or
error value using the output signal of the oscillator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The foregoing and other advantages of the invention will
become apparent upon reading the following detailed description and
upon reference to the drawings in which:
[0022] FIG. 1 is a block diagram showing an example pump rotor
levitation system in accordance with the present disclosure.
[0023] FIG. 2 is a block diagram showing additional features of the
pump system of FIG. 1.
[0024] FIG. 3 is a circuit diagram showing circuit components of
the pump system of FIG. 1.
[0025] FIG. 4 is a mechanical diagram showing bearing and
positioning components of a pump housing of the pump system of FIG.
2.
[0026] FIG. 5 is a flow diagram showing an example method in
accordance with the present disclosure.
[0027] FIG. 6 is a flow diagram showing another example method in
accordance with the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Embodiments are described more fully below in sufficient
detail to enable those skilled in the art to practice the system
and method. However, embodiments may be implemented in many
different forms and the present disclosure should not be construed
as being limited to the embodiments set forth herein. The following
detailed description is, therefore, not to be taken to be limiting
in any sense. For purpose of illustration, discussions of the
technology will be made in reference to its utility as a cardiac
assist blood pump. However, it is to be understood that the
technology may have a variety of wide applications to many types of
turbomachinery including, for example, commercial and industrial
pumps, compressors, and turbines.
[0029] The present disclosure is directed to a
magnetically-levitated pump system that includes a pump and a
controller. The pump and controller are typically positioned remote
from each other and interconnected with a cable. The pump includes
a magnetically-levitated pump and some circuitry. The controller
includes a microprocessor and other circuitry. The pump includes a
position sensor that senses a position of a rotor that is arranged
within a stator of the pump. The position sensor determines a
position of the rotor in a longitudinal direction with respect to
an inlet or outlet of a flow path through the stator.
[0030] The positioning sensor (also referred to as a resonance
sensor) may include a coil that acts as a frequency determining
element of a radio frequency oscillator positioned within a housing
of the pump. The output of the oscillator is directed to a
frequency measuring mechanism, the output of which is directed to
an analog or digital converter to obtain a sensor output. Described
in another way, the sensor coil acts as a resonant member of an
oscillator that varies in accordance with relative axial movement
between the rotor and stator. The oscillator, also positioned
within the pump housing in proximity to the pump, provides an
output signal that is output at a relatively high level (e.g., at
about 1 volt peak to peak) through the cable to the controller
where the controller operates to measure that frequency. The
measured frequency is correlated to an axial position of the rotor
relative to the stator. The output from the controller may be used
as a position value then used by a position altering device of the
pump (e.g., a voice coil) to move the rotor relative to the
stator.
[0031] The circuit components positioned inside the pump housing
may be selected such that the circuitry of the pump system is less
subject to external electromagnetic fields and radio signals. The
circuitry replaces the quadrature sensor and related Wheatstone
bridge used for the coil position sensor in prior devices. In one
example, the circuitry utilizes a Colpitts oscillator or other
oscillators well known in the art that have been updated to use
transistors and require a relatively small number and size for the
surface mount components.
[0032] Referring now to FIG. 1, an example magnetically-levitated
pump system 10 is shown schematically including a position sensor
coil 25 (also referred to as a rotor position sensor or a rotor
position sensor coil), an oscillator 28, a controller 14, and a
rotor positioning device 24 (also referred to as a voice coil 24).
The position sensor coil 25, oscillator 28 and rotor positioning
device 24 are typically positioned within a housing of the pump.
The controller 14 is typically positioned remote from the pump. The
coil position sensor 25 is typically mounted to an exterior of a
stator of the pump and includes a wire coil. A rotor positioned
within the stator may carry or comprise a conductive material. The
rapidly changing magnetic field induced by oscillator current
flowing through the position sensor coil 25 causes currents to be
induced in a conductive surface of the rotor. These currents, in
turn, produce a magnetic field which interacts with the
sense-coil-induced magnetic field, and affect a flow of energy from
a current in the position sensor coil 25, to a magnetic field, and
back to a current in the position sensor coil 25. This change is
reflected as a change in inductance of the coil position sensor 25,
which is a measurable parameter. The change in inductance, in turn,
changes the frequency of the oscillator 28.
[0033] An output of the oscillator 28 is delivered to the
controller 14 and converted to a value that represents a relative
position of the rotor to the stator. This value may be communicated
to a rotor positioning device 24 that adjusts the position of the
rotor relative to the stator. The rotor positioning device 24 may
be a voice coil. The voice coil may comprise a plurality of wire
coils positioned on an exterior of the stator and a magnet carried
by the rotor that is aligned radially with the wire coils of the
voice coil.
[0034] U.S. Published Patent Application No. 2011/0237863 discloses
various components of a magnetically-levitated pump such as the
rotor, stator, magnetic bearings and voice coil, and is
incorporated herein in its entirety by this reference. Many other
types of pumps and motors (e.g., a reciprocating pump) having
different configurations that utilize various technologies may also
be applicable to the present disclosure. FIG. 4 shows schematically
an example magnetically-levitated pump 112 having at least some of
the same or similar components included in pump 12. Pump 112
includes levitation components 122, rotor position components 125,
a stator housing 130, a rotor 132, fixed bearing magnets 134, 136
mounted to the stator housing 130, and suspended bearing magnets
140, 142 carried by the rotor 132. The levitation components 122
include a voice coil 138 mounted to the stator housing 130, and
first and second voice coil magnets 144,146 carried by the rotor
132. The rotor position sensor 125 includes a sensor coil 126
mounted to the stator housing 130. The stator housing 130 includes
a fluid channel 150, an inlet 152 and an outlet 154. The rotor 132
includes first and second ends 156, 158. The first end 156 may
function as a conductive sensor target. The rotor position sensor
125 may operate to determine a position of the rotor 132 with
respect to an axis or other feature of the stator housing 130, such
as a longitudinal position or a lateral position with respect to a
longitudinal or lateral axis of the stator housing 130,
respectively.
[0035] FIG. 2 illustrates additional components of the pump system
10. The pump system 10 includes a pump 12, the controller 14, and a
patient/clinical interface 15. The pump 12 and controller 14 are
typically interconnected with a cable that provides electronic
communication between the pump 12 and controller 14. The
patient/clinical interface 15 may be local to either the pump 12 or
controller 14 (e.g., included in the housing of the controller 14)
or positioned remotely via an electronic connection. The electronic
connection between any of the pump 12, controller 14, and
patient/clinical interface 15 may be wired or wireless, wherein the
wired or wireless connection may be accomplished at least in part
using a communications network such as the Internet.
[0036] The pump 12 may include, in addition to the stator housing
and the rotor positioned within the stator housing, a rotor
position sensor 25, an oscillator 28, a sensor coil 26, a
levitation drive 22, a voice coil 24, and a motor drive 20 that
includes a plurality of pump coils 21. The rotor position sensor
25, levitation drive 22, and motor drive 20 may each include at
least one magnet that is carried by the rotor and positioned within
the stator. The sensor coil 26, voice coil 24, and pump coils 21
are typically all positioned outside of the stator or at least
outside of a flow pathway within which the rotor is positioned.
[0037] The controller 14 comprises one or more microprocessors 36,
a motor control 40, the rotor position sensor 25, a levitation
control 42, a controller monitoring device 46, a data logging
device 48, a battery and charger 50, a power supply 52, a power
management device 54, an external communication 56, and a
levitation system 58 (e.g., a PID, VZP and PWM). The
microprocessors 36 communicate with each of the rotor position
sensor 25, levitation drive 22 and motor drive 20. The rotor
position sensor 25, levitation drive 22 and motor drive 20 may
communicate with the oscillator 28, voice coil 24, and pump coils
21, respectively, via electronic communication provided by a cable
interconnecting the pump 12 and controller 14.
[0038] The patient/clinical interface 15 may include a clinical
user interface 62, a patient user interface 64, and a wall power
interface and charger 66. The clinical user interface 62 may be
provided locally or remotely relative to the controller 14 and pump
12. Similarly, the patient user interface 64 may be carried by the
controller 14 or the pump 12. The clinical user interface 62 and
patient user interface 64 may provide a clinician and patient with
the ability to control, modify, and receive feedback from the pump
12 and controller 14.
[0039] Referring now to FIG. 3, various circuit components of the
pump system 10 are shown. The pump 12 may include the sensor coil
26 connected electronically to the oscillator 28. As described
above, the sensor coil 26 may act as a resonating element for the
oscillator 28. The pump may also include a stator 16 (also referred
to as a stator housing) and rotor 18 (also referred to as a rotor
hub). The sensor coil 26 may be mounted to the stator 16 and
positioned external of a flow pathway of the stator within which
the rotor 18 is positioned.
[0040] An output of the oscillator 28 may be directed to a
multiplier 30 (also referred to as a mixer 30) of the controller
14. Controller 14 also includes a low pass filter 32, a comparator
34, at least one microprocessor 36, and an amplifier 38. The
microprocessor 36 may be an MSP430 processor. The microprocessor 36
may provide a local oscillator signal 37 back to the multiplier 30.
A crystal 39 may be associated with the microprocessor 36 to
provide electronic stability. The microprocessor 36 may include a
timer/comparator input to receive signals from the comparator 34,
and a DAC output connected to the amplifier 38. The amplifier 38
may provide a sensor output 43 that is directed back to levitation
circuitry of pump 12 (e.g., a voice coil rotor positioning device)
to adjust a position of the rotor 18 relative to the stator 16.
Alternatively, the sensor output 43 may be coupled to the
levitation circuitry in a digital fashion, without need of a DAC or
amplifier.
[0041] In one example, the oscillator 28 typically oscillates at
around 250 kHz, and preferably somewhere in the range of about 220
kHz to about 350 kHz. The multiplier 30 may be a diode double
balanced mixer. The multiplier 30 may mix the signal received from
the oscillator 28 with the local oscillator signal 37 received from
the microprocessor 36. In one example, the microprocessor 36 may be
running at about 20 mHz, which frequency may be divided down to
whatever frequency is required for the local oscillator signal 37
for use in calibrating.
[0042] A frequency range received in the signal from pump 12 is
measured, and from that measured frequency a 20 kHz offset to the
local oscillator signal 37 may be used, followed by finding a
nearest integer divisor from 20 mHz that will be close to the local
oscillator signal 37. Typically, some correction factors are
applied such as a gain or an offset to obtain a signal that
accurately represents the rotor position.
[0043] In one example, the oscillator signal coming from oscillator
28 is about 250 kHz, which is nominal within about 250-254 kHz
moving over the range of the rotor positioning sensor. In one
example, the local oscillator signal 37 is preferably set at about
230 kHz. The difference frequency would be about 20 kHz up to about
24 kHz and a sum of the frequencies would be about 480 kHz to about
484 kHz. The signal is then directed through the low pass filter 32
that filters out the summed frequency so that the low frequency
component remains.
[0044] The low frequency component is then directed to the
comparator 34. The comparator 34 may be a squaring comparator that
provides a square wave output in the range of about 20 kHz. The
signal from the comparator 34 may be directed to a timer/comparator
input of the microprocessor 36, which may also be referred to as a
clock input, counter input or high speed counter. In at least one
example, a time interval measurement between when the signal
crosses zero becomes proportionate to a position of the rotor
relative to the stator. The microprocessor 36 corrects for
calibration errors and converts the signal to a number, possibly
represented by a voltage range that is appropriate for use by the
rotor positioning member (e.g., the voice coil).
[0045] By putting the oscillator 28 within a housing of the pump
12, the signal delivered to the microprocessor in the controller 14
and received back from the microprocessor 36 to the rotor
positioning member is much less sensitive to minor voltage changes
that may be induced with the cable that interconnects the pump 12
and controller 14. Some arrangements include positioning the
oscillator 28 at other locations, such as adjacent to the
controller 14 at a location remote from the housing of the pump
12.
[0046] Another aspect of the present disclosure relates to the
interchangeability of the pump 12 and controller 14 with other
pumps and controllers. The calibration constants for the pump may
be stored in memory (e.g., an ID chip) of the pump, and calibration
constants for the controller may be stored in memory of the
controller. For example, the pump may have calibration constants A,
B, C that are stored in memory of the pump. The controller may have
calibration coefficients D and E that are stored in memory of the
controller. When the pump is connected to the controller, an ID
chip of the pump is connected in electronic communication with the
controller. The pump calibration coefficients are downloaded to the
controller. The controller uses those pump coefficients to correct
the frequency of the signal received from the oscillator of the
pump. For example, the pump parameters are used to set the local
oscillator signal 37 in FIG. 3 so that the correct local oscillator
frequency 37 is used for calibrating the frequency that is being
received from the oscillator 28 of the pump.
[0047] In one example, the pump parameters are determined during
manufacture of the pump. The pump is tested during manufacturing to
receive certain data such as, for example, a frequency measurement
from the oscillator when the rotor is moved longitudinally to the
inlet and another frequency measurement when the rotor is moved to
the outlet of the stator. The various pump parameters may be
calculated based on these two frequency measurements. The pump
parameters may be used to determine, for example, the local
oscillator divisor or signal, a pump gain, and a pump offset. Those
parameters are stored in memory of the pump (e.g., on an ID chip of
the pump). Similarly, the controller is tested during manufacturing
to determine a DAC divisor and DAC offset, which is essentially a
first order correction to the sensor output 43 of FIG. 3.
[0048] In one example, the pump includes about 20 to 25 circuit
components as part of the oscillator 28 that are positioned inside
the pump housing. Of these components, 4 to 6 may critically affect
the accuracy of the oscillator. The controller may include multiple
resistors (e.g., preferably about 4 to 5 resistors) that set gains
and offsets for the controller output. The parameters of the pump
and controller are typically relatively stable in the presence of
variations in temperature. Further, a crystal 39, which is
typically stable with changes in temperature, is used in connection
with the microprocessor 36 to even further stabilize the pump
system 10.
[0049] Another aspect related to the pump system disclosed herein
relates to the number of components and the related complexity of
the system corresponding to the number of components. Some types of
pump systems include at least 50 components associated with the
accuracy of the position sensor circuitry. The numerous amplifier
stages and associated gains and offsets for these components all
affect the performance of the pump. The pump of the present
disclosure uses only a few critical circuit components, which are
primarily for the oscillator. The pump circuit components may be
thermally stabilized using known techniques, such as negative
temperature coefficient capacitors and properties of the sensor
coil and the larger capacitors that make up the oscillator. The
pump circuitry may be simpler to manufacture, test and maintain
because of its few number of critical components.
[0050] Another advantage related to the reduced number of
components in the pump system 10 as compared to other pump systems
relates to the power usage of the pump system. Other rotor sensor
systems use as many as at least 100 to 150 circuit components for
the pump and controller, which may consume several watts of power.
The rotor position sensor system of the present disclosure may be
configured to consume power in the order of 60 to 1,000 milliwatts
and more preferably in the range of about 20 to 100 milliwatts. In
scenarios where the pump system 10 is battery-operated, the amount
of power consumption can be an important design factor.
Furthermore, the increased use of power and the number of
components affects the amount of heat generated within the pump
housing and controller housing. The reduced number of components in
the pump system of the present disclosure and the related decreased
amount of heat generated may lead to improved consistency in
performance, increased component life, and increased battery
life.
[0051] Referring now to FIGS. 5 and 6, several example methods of
determining a rotor position in a stator housing are described.
FIG. 5 shows an example method 200 that includes a step 202 of
providing a stator housing having a fluid pathway, a rotor hub
positioned in the fluid pathway, a sensor coil positioned external
to the fluid pathway, a conductive target carried by the rotor hub,
and an oscillator. A step 204 includes changing coupling of the
eddy current target to the sensor coil by moving the rotor hub
longitudinally relative to the stator housing, thereby altering an
inductance of the sensor coil. The sensor coil operates as a
resonating element in the oscillator. A step 206 includes
determining a position of the rotor hub relative to the stator
housing using an output of the oscillator.
[0052] Other steps of method 200 may include shifting a frequency
of a signal output from an oscillator to create a lower frequency
signal, measuring the lower frequency signal, and providing a value
for the measured lower frequency signal that represents a position
of the rotor hub relative to stator housing. Another step for
method 200 may include locking a phase of the signal output from
the oscillator to create a phase locked signal, measuring the phase
locked signal, and providing a value for the measured phase locked
signal that represents a position of the rotor hub relative to the
stator housing. A further method step may include locking a
frequency of the signal output from the oscillator to create a
frequency locked signal, measuring the frequency locked signal, and
providing a value for the measured frequency locked signal that
represents a position of the rotor hub relative to the housing. The
method 200 may also include magnetically-levitating the rotor hub
in the fluid pathway, and controlling a longitudinal position of
the rotor hub relative to the stator housing in response to the
determined position of the rotor hub.
[0053] FIG. 6 illustrates a method 300 of determining a position of
a rotor within a housing in a magnetically-levitating pump system.
The method 300 includes a step 302 of providing a
magnetically-levitating pump system having a pump and a controller.
A step 304 includes providing the pump with a rotor positioned in a
stator, a position sensor positioned outside of the stator, and an
oscillator, wherein the position sensor comprises a coil. A step
306 includes creating resonance in the oscillator with the position
sensor in response to a change in relative axial position of the
rotor to the stator. A step 308 includes processing an output
signal of the oscillator with the controller to create a value
representative of the change in relative axial position. A step 310
includes correcting a position of the rotor based on the value.
[0054] The position of the rotor may be corrected using a voice
coil. The magnetically-levitating pump system may further include a
magnetic bearing and a magnetic motor. The controller may include a
microprocessor configured to determine the rotor position value
using the output signal of the oscillator. The controller may
include a multiplier, a low-pass filter, a comparator and an
amplifier to create an output signal having the value.
[0055] The term "resonant eddy current sensor" as used herein may
generally refer to the class of measuring based on currents induced
in a non-magnetic or non-contacting surface. The resonant eddy
current sensor as disclosed herein may be used for measuring
position based on magnetic or on electrical currents induced by a
magnetic field from a coil that is positioned somewhere that is not
touching the rotor. The term "frequency shifting" as used herein
may relate to shifting the frequency of resonance or the signal
that is the resonant frequency down to a frequency where the signal
may be more readily measured.
[0056] A "phase lock resonant eddy current sensor" may receive the
output of the oscillator 28 of the pump 12 and direct the output
signal to a phase detector (e.g., delta phase) where the output
signal is summed together and integrated. This summed and
integrated signal is returned back for comparing to the oscillator
output. The voltage (VCO) is adjusted to be analogous of the
frequency and is called a control voltage in a phase lock loop.
From there, the voltage may be digitized and used in a levitation
system.
[0057] A phase locked resonant eddy current sensor may have
similarities to a frequency locked resonant eddy current sensor. A
phase locked resonant eddy current sensor measures the phase
between two signals and controls the voltage based on that
comparison. A frequency locked resonant eddy current sensor
measures frequency and adjusts the voltage up and down on a DC arc
to control the frequency.
[0058] The principles of the coil positioning sensor disclosed
herein may be applied to magnetically levitated motor and
magnetically levitated pumps, and specifically to magnetically
levitated blood pumps. Principles disclosed herein may be useful in
other applications outside of blood pumps where accurate
measurements of the rotor position relative to the stator and
obtaining a position signal relatively free of influence from
outside environmental conditions is desired.
[0059] While the invention may be susceptible to various
modifications and alternative forms, specific embodiments have been
shown by way of example in the drawings and have been described in
detail herein. However, it should be understood that the invention
is not intended to be limited to the particular forms disclosed.
Rather, the invention includes all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the following appended claims. It is specifically
noted that any features or aspects of a given embodiment described
above may be combined with any other features or aspects of other
described embodiments, without limitation.
* * * * *