U.S. patent application number 10/688795 was filed with the patent office on 2005-04-21 for method and apparatus for supplying refrigerant fluid.
Invention is credited to Copping, Gareth.
Application Number | 20050081541 10/688795 |
Document ID | / |
Family ID | 34465609 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050081541 |
Kind Code |
A1 |
Copping, Gareth |
April 21, 2005 |
Method and apparatus for supplying refrigerant fluid
Abstract
An apparatus is disclosed for supplying a refrigerant fluid to a
cooling device, such as a cryosurgical probe. An arrangement of
valves may control the supply of fluid to and from the cooling
device. Fluid may flow in a forward direction through the cooling
device for generating cooling by expansion of the fluid in the
cooling device. The apparatus may execute a programmed sequence of
cooling and heating cycles automatically. Backflushing of the fluid
may be used for clearing contaminants from the inlet side of the
cooling device. A pulse width modulated control signal may be used
to control one of the valves to have a variable effective aperture.
A flow rate sensor may detect the flow rate through the cooling
device. The detected flow rate may be used to detect an occurrence
of a blockage and/or for controlling the fluid supplied to the
cooling device. A blockage may be cleared by automatic
backflushing.
Inventors: |
Copping, Gareth; (Woking,
GB) |
Correspondence
Address: |
CHRISTOPHER P. MAIORANA, P.C.
24840 HARPER
ST. CLAIR SHORES
MI
48080
US
|
Family ID: |
34465609 |
Appl. No.: |
10/688795 |
Filed: |
October 17, 2003 |
Current U.S.
Class: |
62/177 ;
62/185 |
Current CPC
Class: |
F25B 9/02 20130101; A61B
2018/0262 20130101; A61B 18/02 20130101 |
Class at
Publication: |
062/177 ;
062/185 |
International
Class: |
F25D 017/00; F25D
017/02 |
Claims
1. Apparatus for supplying refrigerant fluid to a cooling device,
said apparatus comprising: an arrangement of valves for controlling
fluid flow to and from said cooling device; and a control unit
configured to control said arrangement of valves in: (i) a first
operating mode in which said refrigerant fluid flows in a first
direction through said cooling device for generating a cooling
effect in said cooling device; and (ii) a second operating mode in
which said refrigerant fluid flows at least momentarily in an
opposite second direction through said cooling device for
backflushing said cooling device.
2. The apparatus of claim 1, wherein in said second mode, an at
least momentary pressure differential is created across said
cooling device to cause said refrigerant fluid to flow in said
second direction.
3. The apparatus of claim 2, wherein said pressure differential is
greater than 300 psi.
4. The apparatus of claim 2, further comprising first and second
fluid conduits for communicating with said coupling device, and
wherein said control unit is configured in said second operating
mode to control said arrangement of valves to create a head of
pressure directly or indirectly in at least said second conduit,
and to vent pressure from said first conduit during or after
creating said head of pressure.
5. The apparatus of claim 4, wherein said control unit is further
configured to control the arrangement of valves in said first
operating mode to supply refrigerant fluid to said first conduit
and to vent fluid from said second conduit.
6. The apparatus of claim 4, wherein said control unit is
configured to control said arrangement of valves to vent said first
conduit after creating said head of pressure, and wherein said head
of pressure is created in said second conduit by a third operating
mode of supplying said refrigerant fluid through said first conduit
and said cooling device to said second conduit, and blocking
venting of fluid from said second conduit.
7. The apparatus of claim 6, wherein said third operating mode is a
thaw mode for heating said cooling device following a cooling
operation.
8. The apparatus of claim 1, wherein said first operating mode is a
cooling mode of said cooling device, and wherein said second
operating mode is a post-cooling mode subsequent to said cooling
mode.
9. The apparatus of claim 2, wherein said control unit is
configured to perform said second operating mode after each
performance of said first operating mode as part of a combined
cycle.
10. Apparatus for supplying refrigerant fluid to a cooling device,
said apparatus comprising: a first valve for controlling fluid flow
to said cooling device; and a control unit configured to generate a
pulse modulated control signal for controlling said first valve,
wherein said pulse modulated signal is effective to control said
first valve in a partly open condition.
11. The apparatus of claim 10, wherein said pulse modulated control
signal is a pulse width modulated signal.
12. The apparatus of claim 11, wherein said first valve is
configured to open to an extent responsive to a duty ratio of said
pulse width modulated signal.
13. Apparatus for supplying refrigerant fluid to a cooling device,
said apparatus comprising: a first valve for controlling fluid flow
to said cooling device; and a control unit configured to generate a
control signal for controlling an extent of opening of said first
valve, wherein said control unit is configured, in response to a
command to open said first valve, to generate said control signal
to open said valve gradually over an interval of time, whereby a
pressure of said refrigerant gas supplied to said cooling device
increases gradually.
14. The apparatus of claim 13, wherein said control signal is a
pulse modulated signal.
15. Apparatus for supplying refrigerant fluid to a cooling device,
said apparatus comprising: an arrangement of valves for controlling
fluid flow to and from said cooling device; and a control unit
configured to control said arrangement of valves in at least a
first mode of operation for generating cooling in said cooling
device, and a second mode of operation for generating heating in
said cooling device; said control device comprising a storage
device for storing data defining a program sequence of at least one
cycle of said first and second modes, and said control unit being
configured to execute said program sequence.
16. The apparatus of claim 15, further comprising an input device
for inputting a command to said control unit, wherein said control
unit is responsive to said command to begin execution of said
program sequence.
17. The apparatus of claim 16, wherein said input device comprises
a foot-switch.
18. The apparatus of claim 15, wherein said storage device is
configured to store a plurality of selectable program
sequences.
19. Apparatus for supplying refrigerant fluid to a cooling device,
said apparatus comprising: an arrangement of valves for controlling
a flow of said refrigerant fluid to and from said cooling device; a
flow rate sensor for sensing a flow rate of said refrigerant fluid
and for generating a flow rate signal; and a control unit
responsive to said flow rate signal and configured to control said
arrangement of valves.
20. The apparatus of claim 19, wherein said flow rate sensor is
coupled to a low pressure side of said cooling device.
21. The apparatus of claim 19, wherein said control unit is
configured to detect an occurrence of a blockage in said cooling
device when said flow rate signal indicates an abnormally small
flow rate of said refrigerant fluid.
22. The apparatus of claim 21, wherein said control unit is
configured to perform an unblocking operation in response to
detection of a blockage.
23. The apparatus of claim 22, wherein said unblocking operation is
a backflush of said refrigerant fluid through said cooling
device.
24. The apparatus of claim 19, wherein said control unit is
configured to adjust a pressure of said refrigerant fluid supplied
to said cooling device in response to the flow rate signal.
25. Apparatus for supplying a refrigerant fluid to a cooling
device, the apparatus comprising: a fluid supply conduit for
receiving refrigerant fluid from a supply source; first and second
coupling conduits for communicating with said cooling device; a
first valve coupled between said fluid supply conduit and said
first coupling conduit for selectively applying fluid pressure to
said first coupling conduit; a second valve coupled between said
fluid supply conduit said second conduit for selectively applying
fluid pressure to said second coupling conduit; a third valve
coupled between said first coupling conduit and a vent for
selectively venting said first coupling conduit independently of
said second coupling conduit; a fourth valve coupled between said
second coupling conduit and a vent for selectively venting said
second coupling conduit independently of said first coupling
conduit.
26. The apparatus of claim 25, further comprising a flow resistance
coupled in series with said second valve between said fluid supply
conduit and said second conduit.
27. The apparatus of claim 25, further comprising a flow rate
sensor coupled in series with the fourth valve between said second
coupling conduit and said vent.
28. The apparatus of claim 27, wherein said flow rate sensor is
coupled between said fourth valve and said vent.
29. The apparatus of claim 25, wherein said apparatus is configured
to operate in a cooling mode for supplying refrigerant fluid in a
forward direction through said cooling device, wherein said first
valve and said fourth valve are open, and said second valve and
said third valve are closed.
30. The apparatus of claim 25, wherein said apparatus is configured
to operate in a heating mode in which a head of pressure is created
directly or indirectly in each of said first and second supply
conduits, wherein at least one of said first and second valves is
open, and said third valve and said fourth valve are closed.
31. The apparatus of claim 25, wherein said apparatus is configured
to operate in a backflushing mode in which a head of pressure is
backflushed from said second conduit through said cooling device to
said first conduit, wherein said first valve and said fourth valve
are closed, and said third valve is open.
32. The apparatus of claim 25, wherein said first and second valves
are normally closed valves, and said third and fourth valves are
normally open valves.
33. A method of operation of an apparatus for supplying refrigerant
fluid to a cooling device, the method comprising: controlling an
arrangement of valves for controlling fluid flow to and from said
cooling device, in: (i) a first operating mode in which said
refrigerant fluid flows in a first direction through said cooling
device for generating a cooling effect in said cooling device; and
(ii) a second operating mode in which said refrigerant fluid flows
at least momentarily in an opposite second direction through said
cooling device for backflushing said cooling device.
34. A method of operation of an apparatus for supplying fluid
refrigerant to a cooling device, the method comprising: generating
a pulse modulated command signal indicative of a commanded extent
of valve opening; and applying said pulse modulated command signal
to a first valve configured for controlling refrigerant fluid flow
to said cooling device, to open said valve to said commanded
extent.
35. A method of operation of an apparatus for supplying refrigerant
fluid to a cooling device, the method comprising: providing data
representing a programmed sequence of operating modes of said
apparatus, said operating modes including a cooling mode and a
heating mode; and executing said program sequence automatically by
advancing from one mode to a next mode in a manner defined by the
programmed sequence.
36. A method of operation of an apparatus for supplying fluid
refrigerant to a cooling device, the method comprising: sensing a
flow rate of said refrigerant fluid; and controlling, in response
to said sensed flow rate, an arrangement of valves configured to
control fluid flow to and from said cooling device.
Description
FIELD OF THE INVENTION
[0001] The present invention may relate to supplying refrigerant
fluid to, for example, a cooling device for generating a cooling
effect based on Joule-Thompson expansion of the fluid. The
invention may be especially useful in the field of medical or
surgical use. The cooling device may, for example, be a cooling
probe.
BACKGROUND TO THE INVENTION
[0002] The Joule-Thompson principle of isenthalpic expansion of
certain refrigerant fluids (e.g., gases) through a micro expansion
orifice has long been used in the medical field to create a
freezing effect. Typically, the expansion orifice is located at the
tip of a probe through which the refrigerant fluid is driven under
pressure. The operation of the probe is controlled by a fluid
supply apparatus including one or more valves or regulators for
controlling the flow of fluid in the probe. A conventional fluid
supply apparatus is described, for example, in WO 00/35362.
[0003] A significant problem is that the micro expansion orifice in
the probe is vulnerable to blocking by foreign matter such as dust
particles or other contaminants that may be contained in the
refrigerant fluid or otherwise enter the probe. A blocked probe
normally has to be returned to a service center or factory for
thorough cleaning before the probe can be used reliably again. For
many cyro-surgeons and probe operators, the problem of probe
blocking is considered to be a highly inconvenient, yet regular,
occurrence that has to be tolerated as a result of the nature of
the probe design.
[0004] Other problems remain in terms of difficulty of use of the
fluid supply apparatus and the probe, difficulty of handling fault
conditions such as a blocked or faulty probe, and difficulty of
reducing the risk of occurrence of probe blockage.
SUMMARY OF THE INVENTION
[0005] A first aspect of the present invention may be to provide an
at least momentary backflushing of fluid through a cooling device.
The backflushed fluid may be the same fluid as that used as the
refrigerant. The backflushing may be effective to clear or dislodge
any foreign matter that may have been driven into an expansion
orifice of the cooling device by the usual flow of fluid in the
forward direction.
[0006] The backflushing may be controlled by an arrangement of
valves. The valves may be configured in a first mode of operation
in which refrigerant fluid may be caused to flow in a forward
direction through the cooling device. The valves may further be
configured in a second mode of operation in which fluid may be
caused to flow, at least momentarily, in a reverse direction
through the cooling device. In one form, the second mode may be a
mode in which the cooling device may be pressurized such that
pressure may develop in both an inlet side and outlet side of the
cooling device, whereafter the inlet side may be vented to cause
pressurized fluid on the outlet side to backflush through the
cooling device. Such a configuration may generate an abrupt
pressure differential or pressure wave that may be extremely
effective to dislodge foreign matter blocking the cooling
device.
[0007] The backflushing may be carried out when a blockage is
detected in use. Additionally or alternatively, the backflushing
may be carried out routinely at intervals in use of the cooling
device. For example, the backflushing may be carried out following
each freeze and/or thaw cycle (or each combined freeze-thaw cycle)
of the cooling device. Such frequent backflushing has been found to
be highly effective in reducing the risk of occurrence of a
blockage, even if the cooling device is used many times.
[0008] A second aspect of the invention may be to use, as a valve
between a high pressure refrigerant fluid source, and an inlet side
of a cooling device, a valve that is responsive to a pulse
modulated electronic control signal. The pulse modulated signal may
be a pulse width modulated signal (PWM), or a pulse density
modulated (PDM) signal. A pulsed valve may have a fast response,
and be less expensive and yet more reliable and durable than an
equivalent servo driven valve.
[0009] A third aspect of the invention may be to implement an
automatic gradual application of pressure to an inlet side of a
cooling device, instead of an abrupt application of refrigerant
fluid at high pressure. Such a gradual application of pressure may
be referred to as a "soft start". The gradual application of
pressure may help reduce the risk of blockage in the cooling device
by avoiding an abrupt pressure wave in the forward direction
through the cooling device that may otherwise force foreign matter
on the inlet side of the cooling device into the expansion
orifice.
[0010] A fourth aspect of the invention may be for a control unit
of the fluid supply apparatus to be provided with one or more
program sequences each of one or more freeze-thaw cycles. The
control unit may be responsive to a manual start command from an
operator to begin performing a selected program sequence.
Thereafter, the control unit may be configured to automatically
advance through the program sequence without any further input from
the operator. The control unit may be responsive to an interrupt
command from the operator to enable the program sequence to be
halted at any moment if desired by the operator.
[0011] A fifth aspect of the invention may be to measure the flow
rate of refrigerant fluid passing through the cooling device, at
least in one or more certain modes of operation of the cooling
device. A flow rate sensor may be coupled to a low pressure side of
the cooling device. Coupling the flow rate sensor on the low
pressure side may enable a less expensive flow rate sensor to be
used.
[0012] The measured flow rate may be used to detect the occurrence
of a blockage in the cooling device. For example, a blockage may be
identified when the flow rate is zero or unusually small. In
response to a detected blockage, a warning signal may be generated.
Additionally or alternatively, a self-unblocking operation may be
initiated to try to clear the blockage. The self-unblocking
operation may include backflushing fluid through the cooling device
in an opposite direction to the normal flow during cooling.
[0013] The measured flow rate may also, or alternatively, be used
in combination with a measured fluid pressure and/or temperature,
in a feedback loop for regulating the fluid pressure applied to the
cooling device in order to control the performance of the cooling
device.
[0014] Other features, objects and advantages of the invention may
be defined in the claims and/or apparent from the following
description of a preferred embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] A non-limiting preferred embodiment of the invention is now
described by way of example with reference to the claims and
accompanying drawings in which:
[0016] FIG. 1 is a schematic diagram of fluid and control circuitry
for a refrigerant fluid supply apparatus;
[0017] FIG. 2 is a schematic flow diagram illustrating operating
modes of the fluid supply apparatus;
[0018] FIGS. 3-6 are schematic flow diagram illustrating details of
FIG. 2;
[0019] FIGS. 7 and 8 are schematic representations of preset
freeze-thaw programs;
[0020] FIG. 9 is a schematic flow diagram illustrating performance
of a predefined sequence of free-thaw cycles; and
[0021] FIGS. 10(a)-(c) are schematic representations of a valve
control signal useable in the apparatus of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] FIG. 1 may generally illustrate a fluid supply apparatus 10
for supplying and controlling the flow of a refrigerant fluid to a
cooling device 12. The cooling device 12 may be detachably
connectible to a coupling 18 of the apparatus 10. The cooling
device 12 may be a medical or surgical probe. The cooling device 12
may include a small orifice (depicted schematically at 14) for
generating a freezing effect by the Joule-Thompson principle of
isenthalpic expansion when fluid is forced through the orifice 14
from an inlet side 12a to an outlet side 12b. The terms "inlet
side" and "outlet side" may refer to a normal direction of fluid
flow through the cooling device 12 for generating the intended
freezing effect. The refrigerant fluid may be any suitable fluid
for generating significant cooling upon isenthalpic expansion. Such
a fluid may often be referred to as a Joule-Thompson fluid and may
be a gas. For example, the gas may be nitrous oxide.
[0023] The supply apparatus 10 may generally comprise a first
arrangement of valves V1-V4 for controlling a flow of the
refrigerant fluid through (e.g. to and/or from) the cooling device
12, and a second arrangement of valves V5-V8 for selecting an
active one of a plurality of sources 15a-d of the refrigerant fluid
to supply to a fluid supply node 16 in the apparatus. The normal
fluid pressure from the active source 15a-d at the fluid supply
node 16 may typically be between 650 and 900 psi.
[0024] In more detail, a first valve (or "freeze valve") V1 may be
coupled between the fluid supply node 16 and a first coupling port
(e.g., first coupling conduit) 18a to the inlet side 12a of the
cooling device 12. The first valve V1 may supply fluid to the
coupling port 18a. A second valve (or "purge valve") V2 may be
coupled between the fluid supply node 16 and a second coupling port
18b (e.g., second coupling conduit) to the outlet side 12b of the
cooling device 12. The second valve V2 may supply fluid to the
second coupling port 18b. A pressure reducing resistance or
constriction or shunt 20 may be coupled in series with the second
valve V2 for reducing the pressure in response to fluid flow
through the second valve V2. The first and second valves V1 and V2
may collectively be referred to as "supply valves" for delivering
pressurized fluid to the inlet and outlet sides 12a, and 12b, of
the cooling device 12.
[0025] A third valve (or "inlet vent valve") V3 may be coupled
between the first coupling port 18a and an exhaust port 22 for
venting spent fluid from the apparatus. The third valve V3 may
selectively vent the first coupling port 18a independently of the
second coupling port 18b. A fourth valve (or "exhaust vent valve")
V4 may be coupled between the second coupling port 18b and the
exhaust port 22. The fourth valve V4 may selectively vent the
second coupling port 18b independently of the first coupling port
18a. Although a single exhaust port 22 may be illustrated, the
third and fourth valves V3 and V4 may alternatively be coupled to
different exhaust ports or vents. A flow rate sensor F may be
coupled in series with the fourth valve V4 for measuring the flow
through the fourth valve V4. The flow rate sensor may be coupled
via the fourth valve V4 to the second coupling port 18b, which may
be referred to as a low pressure side of the cooling device 12. The
flow rate sensor F may be coupled between the exhaust port 22 and
the fourth valve V4 so that the fourth valve V4 may be used to
isolate the flow rate sensor F from an excessive pressure. A
parallel shunt 24 may be coupled in parallel with the flow rate
sensor F, for enabling the flow rate sensor F to be used to sense a
higher flow rate than the through-flow capacity of the flow rate
sensor F alone. The flow rate sensor F may enable the flow of fluid
through the cooling device 12 to be monitored, so that any
occurrence of a blockage may be detected. The third and fourth
valves V3 and V4 may collectively be referred to as "vent valves"
for venting the inlet and outlet sides 12a and 12b of the cooling
device 12.
[0026] The first and second valves V1 and V2 may be normally-closed
valves. The third and fourth valves V3 and V4 may be normally-open
valves. Such an arrangement may provide a fail-safe mode, should
any of the valves fail. The first and second valves V1 and V2 may
fail-safe closed, such that refrigerant fluid is shut off by each
valve. The third and fourth valves V3 and V4 may fail-safe open,
such that the any fluid pressure in the cooling device 12 may be
vented through the exhaust port 22.
[0027] An electronic control unit 26 may generate respective
control signals VCS1, VCS2, VCS3 and VCS4 for controlling the
valves V1-V4. The electronic control unit 26 may receive a flow
rate signal FS generated by the flow rate sensor F. The electronic
control unit 26 may also receive first and second pressure signals
PS1 and PS2 from first and second fluid pressure sensors P1 and P2.
The first pressure sensor P1 may be coupled to sense the fluid
pressure at the fluid supply node 16. The first pressure signal PS1
may provide a direct indication of the fluid supply pressure from
the active supply source, as described later. The second pressure
sensor P2 may be coupled to sense the fluid pressure at the first
coupling port 18a. The second pressure signal PS2 may provide an
indication of the pressure applied to the cooling device 12 in
normal use, and may also be used to pressure-test the cooling
device 12 to detect leaks, as described later.
[0028] The electronic control unit 26 may further receive one or
more input and/or command signals from a remote control device 28.
The remote control device may, for example, be a foot switch. An
advantage of a foot switch is that an operator may control the
apparatus 10 without contaminating his or her hands, if the
operator requires sterile conditions to be maintained. The
electronic control unit 26 may further receive one or more input
and/or command signals from input switches 30 mounted on a control
panel of the apparatus 10. The electronic control unit 26 may
further receive a temperature signal from a temperature sensor (not
shown) if such a temperature sensor is provided in the cooling
device 12.
[0029] Referring to FIG. 2, the control unit 26 may control the
apparatus 10 in one or more operation modes. The modes may include
rest mode 31, a pressure test mode 32, a purge mode 34, a freeze or
cooling mode 36, a thaw or heating mode 38, a backflush mode 40
and/or an unblock mode 59. The rest mode 31 may correspond to the
fail-safe condition of the first to fourth valves V1-V4. The
operation cycles of the apparatus 10 may begin and/or end (e.g.,
loop back to) the rest mode 31.
[0030] When a cooling device 12 may be connected to the coupling
18, the control unit 26 may firstly initiate the test mode 32 to
test whether the cooling device is adequately pressure tight.
Referring to FIG. 3, at step 42 the first to fourth valves V1-V4
may all set to their closed condition. At step 44, the first valve
V1 and/or the second valve V2 may be opened to pressurize the
cooling device 12 from the fluid supply node 16. The cooling device
may be pressurized to the full pressure of the fluid supply node
16. The first valve V1 and/or second valve V2 may be held open for
a predetermined period of time, or until the pressure measured by
the second pressure sensor P2 may have stabilized. At step 46, the
pressure measured by the second pressure sensor P2 may be recorded,
and the first valve V1 and/or second valve V2 may again be closed,
so that the cooling device 12 is again isolated, but in a
pressurized state. At step 48, after a predetermined test duration,
the pressure measured by the second pressure sensor P2 may again be
recorded, and compared with the previously recorded value. When the
two pressure values are the same (or differ by less than a certain
allowable tolerance), the cooling device 12 may be considered to be
adequately pressure tight, and acceptable for use. When the two
pressure values are not the same (or differ by more than the
allowable tolerance), the cooling device 12 may be considered to be
leaky. In the case of a leaky device, the control unit 26 may
inhibit any further operation with that cooling device 12. A leaky
device may be potentially unsafe. For example, there may be risk
that leaked refrigerant fluid may enter a patient's blood stream
should the cooling device be used on a patient, or there may be
risk of the cooling device 12 losing structural integrity.
[0031] After step 48, the pressure in the cooling device 12 may be
vented at step 50 by opening the third valve V3 and/or the fourth
valve V4. The third valve V3 may be opened before the fourth valve
V4 in order to allow most of the pressure to vent through the third
valve V3 before the fourth valve V4 is opened. Opening the third
valve V3 before the fourth valve V4 may protect the flow rate
sensor F from an excessive flow rate outside its normal range.
Opening the third valve V3 before the fourth valve V4 may also
generate an at least momentary backflushing of high pressure fluid
through the cooling device 12 (for example, fluid under pressure on
the outlet side 12b may flow in a reverse direction through the
orifice 14 to vent via the inlet side 12a). Such high pressure
and/or abrupt backflushing of fluid has been found to be extremely
useful to clear any foreign matter at least from the vicinity of
the orifice 14 of the cooling device 12, and hence reduce the risk
of blockage at the orifice 14.
[0032] When the cooling device 12 may have successfully passed the
pressure test 32, the operation may loop back to the rest mode 31
before the purge mode 34 is invoked, or may proceed immediately to
a purge mode 34. The purge mode 34 may be effective to remove
accumulated moisture from the cooling device 12. Referring to FIG.
4, at step 52, all of the first to fourth valves V1-V4 may
initially be set closed. At step 54, the second valve V2 and the
third valve V3 may be opened, to create a flow of fluid from the
fluid supply node 16 via the second valve V2 and the pressure
reducing shunt 20 to the outlet side 12b of the cooling device 12.
The flow of fluid may be vented from the inlet side 12a of the
cooling device, through the third valve V3 to the exhaust port 22.
In the purge mode 34, the pressure of the fluid may be reduced to a
modest level by the effect of the pressure reducing shunt 20 while
fluid is flowing. The modest pressure level may, for example be
less than 300 psi, or less than 250 psi. The flow may be maintained
for a predetermined period of time effective to purge moisture from
the apparatus 10 and the cooling device 12. At the end of the purge
mode, the flow of fluid may be halted at step 56 by closing the
second valve V2. The fourth valve V4 may be opened at step 58 to
vent any residual pressure on the outlet side 12b of the cooling
device 12.
[0033] Following the purge mode 34, the operation may return to the
rest mode 31 awaiting a command to begin a freeze-thaw operation.
In a freeze-thaw operation, the control unit 26 may initiate one or
more cycles of the freeze mode 36, thaw mode 38 and backflush mode
40. The cycle may, for example, be initiated in response to a
command from the remote control unit 28. Referring to FIG. 5, the
freeze mode 36 may be entered at step 60 by setting the second and
third valves V2 and V3 shut, and by opening the first and fourth
valves V1 and V4. Fluid at high pressure may flow from the fluid
supply node 16 via the first valve V1 to the inlet side 12a of the
cooling device 12. The high pressure fluid may flow in the forward
direction through the orifice 14, creating cooling by the
Joule-Thomson effect. The expanded fluid may vent from the outlet
side 12d of the cooling device via the fourth valve V4 and the flow
rate sensor F to the exhaust port 22. The second pressure sensor P2
and the flow rate sensor F may provide useful indications of the
state of the fluid flow and/or operation of the cooling device 12.
In particular, the flow rate signal FS from the flow rate sensor F
may provide a direct indication of whether fluid is flowing freely
through the cooling device 12, or whether flow may be restricted or
completely stopped, for example, by a blockage in the cooling
device 12. When a blockage is detected, then the control unit 26
may invoke the unblock mode 51 (described below) to try to clear
the blockage.
[0034] The duration of the freeze mode 36 may be predetermined by a
preset program within the control unit 26, or it may be controlled
manually by an operator, for example, by using the remote control
device 28. At the end of the freeze mode 36, operation may proceed
to the thaw mode 38. At step 62, the fourth valve V4 may be closed
to halt the venting of fluid from the outlet side 12b of the
cooling device 12 through the exhaust port 22. A thaw or defrost
effect may be generated in the cooling device 12 by progressive
re-pressurization of the fluid trapped on the outlet side 12b of
the cooling device 12. As an optional step 64, the second valve V2
may be opened to increase the rate of pressurization of the outlet
side 12b, and hence generate a more rapid thaw effect. The duration
of the thaw mode 38 may be predetermined by a preset program within
the control unit 26, or controlled manually by the operator (for
example, using the remote control device 28).
[0035] Following the thaw mode 38, operation may proceed to the
backflush mode 40. At step 66, the cooling device 12 may be
isolated from the fluid supply node 16, but kept in the pressurized
state. For example, at step 66, the first valve V1 may be closed to
halt the supply of refrigerant fluid to the inlet side 12a of the
cooling device 12. If at step 64 the second valve V2 may have been
opened during the thaw mode 38, the second valve V2 may also be
re-closed at step 66. At step 68, the third valve V3 may be opened
to allow the trapped fluid to vent from the inlet side 12a of the
cooling device 12. In a similar manner to step 50 described above,
opening the third valve V3 may generate an at least momentary
backflushing of fluid through the orifice 14, which has been found
to be extremely effective for reducing the risk of blockage at the
orifice 14. The backflush mode 40 may be used at the end of each
freeze-thaw cycle. Such regular high-pressure backflushing can
extend the usability of the cooling device 12 considerably compared
to a conventional fluid supply apparatus which does not provide the
same backflush operation. In particular, the cooling device 12 may
be used numerous times without blocking, in contrast to the high
risk of blocking when a cooling device is driven by a conventional
gas supply apparatus.
[0036] After the backflush mode 40, operation may loop back to the
freeze mode 36 if, for example, a sequence of multiple freeze-thaw
cycles may be used as part of the same treatment. A sequence of
multiple freeze-thaw cycles may be controlled automatically be the
control unit 26, or manually, for example, using the remote control
device 28. After completion of the freeze-thaw cycles, the control
unit 26 may return the apparatus to the rest mode 31.
[0037] As mentioned above, when a blockage is detected during the
freeze mode 36, operation may branch to the unblock mode 59. The
operation of the unblock mode 59 may be similar to the backflushing
described previously for steps 50 and 68. Referring to FIG. 6, at
step 70, the cooling device 12 may be pressurized to a high
pressure, by opening the first valve V1 and/or the second valve V2
while closing the third valve V3 and the fourth valve V4. Then, at
step 72, the fluid may be backflushed through the orifice 14 by
opening the third valve V3 while closing at least the first valve
V1. The second valve V2 may remain open or closed during
backflushing. The fourth valve V4 may remain closed during the
backflushing, to avoid any pressure loss on the outlet side 12b of
the cooling device 12. After backflushing, the fourth valve V4 may
be opened at step 74 to vent any residual pressure on the outlet
side 12b. During step 74, the flow rate measured by the flow rate
sensor F may be monitored to detect whether a significant amount of
fluid may vent through the fourth valve V4. If the blockage has
been cleared, then very little fluid may vent through the fourth
valve V4. A large quantity of fluid venting through V4 may indicate
that the blockage may not have been cleared. One or more backflush
cycles may be performed in sequence to try to clear a blockage of
the cooling device. Following the unblock mode 59, operation may
return to the freeze mode 36. Alternatively, the control unit 26
may signal a warning or a report to the operator to indicate that a
probe blockage has occurred, and/or to indicate whether or not the
blockage has been cleared.
[0038] In the foregoing description, backflushing may be achieved
by pressurising both the inlet side 12a and the outlet side 12b of
the cooling device 12, and opening the third valve V3 to vent the
fluid from the inlet side 12a. Opening the third valve V3 while
keeping the fourth valve V4 closed may generate an at least
momentary flow of a quantity of pressurized fluid from the outlet
side 12b through the orifice 14 to the inlet side 12a, thereby
backflushing fluid through the orifice. The backflushing may
generate an abrupt pressure burst or pressure wave across the
orifice, which is extremely effective in clearing foreign matter
from the orifice 14. The magnitude of a backflush pressure
differential across the orifice may be at least, or greater than,
any of: 300 psi, 350 psi, 400 psi, 450 psi, 500 psi, 550 psi, 600
psi, 650 psi, 700 psi, 750 psi, 800 psi, or 850 psi. As an
alternative to a momentary flow, a separate back-flush valve V9 may
be coupled from the fluid supply node 16 to the second coupling
port 18b. The back flush valve V9 may be operated to provide a
continuous flow of high pressure fluid to the outlet side 12b of
the cooling device, for continuous backflushing through the orifice
14.
[0039] Referring to FIG. 1, the control unit 26 may comprise a
storage device 80 for storing one or more program sequences of
freeze-thaw cycles. The storage device 80 may be a non-volatile
storage device. The storage device may, for example, comprise a
non-volatile semiconductor memory, or magnetic or optical media.
The program sequences may be programmable by the operator, or
predefined within the control unit 26. FIG. 7 may illustrate a
first example format for storing the one or more program sequences
82a, 82b. Referring to FIG. 7, each program sequence 82a, 82b may
include data representing at least durations 84 of a sequence of
freeze modes 36 and thaw modes 38. The durations 84 may include
freeze mode durations 84a and thaw mode durations 84b. In the first
example format, separate data may be provided for each mode in the
program sequence 82. Providing separate data may enable the
duration of freezing and thawing to be varied at different parts of
the sequence. For example, the first sequence 82a may define a
first freeze cycle of 3 minutes, a second thaw cycle of 30 seconds,
a third freeze cycle of 2 minutes, and a fourth thaw cycle of 20
seconds. The second sequence 82b may define a first freeze cycle of
3 minutes, a second thaw cycle of 30 seconds, a third freeze cycle
of 3 minutes and a fourth freeze cycle of 30 seconds.
[0040] FIG. 8 may illustrate a second example format for storing
one of more program sequences 86a, 86b in a special case in which
the durations of the freeze modes 36 and thaw modes 38 may not vary
throughout the program sequence. Referring to FIG. 8, each program
sequence 86a, 86b may comprise data representing at least a
duration 88a of a single freeze mode 36, a duration of a single
thaw mode 38, and a number 88c of repetitions of the free-thaw
cycles in the program sequence. For example, a first sequence 86a
may define 2 repetition of cycles of a 3 minute freeze and a 30
second thaw. The first sequence 86a may be the same as the sequence
82b described with respect to FIG. 7. A second sequence may define
3 repetition cycles of a 3 minute freeze and a 30 second thaw.
[0041] The number of program sequences 82 or 86 may depend on a
specific application for which the apparatus 10 is intended. For
example, only a single program sequence 82 or 86 may be provided in
some applications. An operator may select the single program
sequence 82 or 86, or may select between plural program sequences
82 or 86, using the selectors 30. Referring to FIG. 9, once a
program sequence has been selected, at step 90 the control unit 26
may be responsive to a "start" command from an operator. The
"start" command may be inputted through one of the input switches
30 or through the remote control device 28. Once the "start"
command has been received, operation may proceed to step 92 at
which the selected program sequence may be retrieved from the
storage device 80 and the defined freeze-thaw cycles of the program
sequence may be performed. For example, the sequence of freeze-thaw
cycles may be performed one after the other without any further
inputs from the operator. During step 92, the control unit 26 may
be responsive to an interrupt signal from the operator for halting
the program sequence. The interrupt signal may be inputted through
the input switches 30 or through the remote control device 28. When
the interrupt signal is received, operation may proceed to step 94
at which the program sequence may be halted. For example, the first
and second valves V1 and V2 may be closed, and the third and fourth
valves V3 and V4 opened. The third valve V3 may be opened before
the fourth valve V4, in order to protect the flow rate sensor F, in
a similar manner to that described for step 50. Alternatively, at
step 94, the thaw mode 38 may be invoked in order to immediately
reverse any freezing at the cooling device 12. The automatic
performance of a program sequence may enable the operation of the
cooling device 12 and the supply apparatus 10 to be simplified, and
enable surgeons not familiar with manually operation to use the
apparatus 10 with ease. Moreover, when the remote control device 12
may be used to provide the start command and/or the interrupt
command, the operator need not contaminate his or her hands if
sterile conditions are preferred. This may enable a procedure to be
carried out by a single person, rather than involving one person to
hold and position the cooling device (in sterile conditions) and
another person to manipulate the controls of the refrigerant supply
apparatus.
[0042] Referring again to FIG. 1, each of the fluid supply sources
15a-d may comprise a replaceable fluid cylinder. The cylinders may
be mountable within the apparatus 10. Each source 15a-d may be
coupled via a non-return valve 100a-d and a filter 102a-d to a
respective one of fifth, sixth, seventh and eighth valves V5-V8,
respectively. The fifth to eighth valves V5-V8 may be coupled to
the fluid supply node 16 to enable fluid to be drawn from a
selected one of the sources 15a-d, and fed to the fluid supply node
16. A function of the filters 102a-d may be to remove at least some
dust particles or other foreign matter from the supplied fluid, in
order to reduce the risk of blockage of the cooling device 12. The
control unit 26 may be responsive to the pressure measured by the
first pressure sensor P1 to determine the state of a currently
selected one of the sources 15a-d. When the pressure may drop below
a predetermined threshold indicative of the source 15a-d running
nearly empty, the control unit 26 may operate respective valves of
the fifth to eighth valves V5-V8 to automatically decouple the
depleted source, and to select instead another source. Such
automatic operation may be performed while fluid is being supplied
to the cooling device 12, so that the operation of the cooling
device 12 may not be interrupted.
[0043] The components within the broken line 104 of FIG. 1 may
conveniently be mounted on an integral manifold unit (not shown)
having conduit bores and chambers for forming the fluid flow paths
indicated in FIG. 1.
[0044] The first to eighth (or ninth) valves V1-V8 (and V9) may be
electrically operated valves. The valves may, for example, be
solenoid operated valves. The first valve V1 may be configured to
have a variable aperture, to provide a variable flow control
between a fully open condition and a fully closed condition. For
example, the first valve V1 may be a variable servo controlled
valve. Alternatively, the first valve V1 may be of a type intended
to be driven by a modulated signal for controlling the first valve
V1 according to a degree of modulation. For example, referring to
FIG. 10, the first control signal VCS1 may be a pulse modulated
signal. The pulse modulated signal may be a pulse width modulated
(PWM) signal. The degree of opening of the first valve V1 may be
controlled by a duty ratio of the PWM signal. FIG. 10a may
illustrate a first example of the control signal VCS1 having a high
duty ratio of on-time:off-time, for controlling the first valve V1
to have a large aperture (e.g., almost completely open). FIG. 10b
may illustrate a second example of the control signal VCS1 having
an approximately 50% duty ratio of on-time:off-time, for
controlling the first valve V1 to have a medium aperture (e.g.
approximately half-way open). FIG. 10c may illustrate a third
example of the control signal VCS1 having a small duty ratio of
on-time:off-time, for controlling the first valve V1 to have a
small aperture (e.g., almost closed). The control unit 26 may
control the duty ratio of the first control signal VCS1 to be
substantially continuously variable, or to have a predetermined
number of quantized values. The frequency of the first control
signal VCS1 may be between 100 Hz and 1000 Hz. Depending on the
frequency, a shutter (not shown) of the first valve V1 may either
physically oscillate between the fully open and closed states in
accordance with each pulse of the control signal VCS1, or the
shutter may effectively hover between the fully open and closed
states, at a mean position determined by the duty ratio of the
control signal VCS1. A pulsed valve may be any of less expensive,
more reliable, and/or more durable than an equivalent servo driven
valve.
[0045] Variable flow control of the first valve V1 (either by using
a pulsed valve or a servo driven valve) may provide additional
advantages. A gradual start (or "soft start") of the freeze cycle
36 may be effected by gradually increasing the fluid pressure
applied at the inlet side 12a of the cooling device, instead of
abruptly applying full pressure to the inlet side 12a in the
forward direction. A gradual increase in pressure may reduce the
risk of blockage at the orifice 14 by avoiding an abrupt pressure
wave that could force dust or other foreign matter on the inlet
side 12a to be driven into the orifice 14.
[0046] Furthermore, the control unit 26 may be configured to
determine an optimum state of the first valve V1 that may optimise
the use of the refrigerant fluid. The control unit 26 may be
responsive to the signals from the second pressure sensor P2 and
the flow rate sensor F to control the first valve V1. For example,
the fluid use may be optimised to achieve a flow rate that produces
an adequate cooling effect while consuming fluid efficiently.
Alternatively, the fluid use may be optimised to achieve a maximum
cooling effect.
[0047] A further advantage of a variable flow of the first valve V1
may that the first valve V1 may be controlled to provide a modest
pressure level of refrigerant fluid, for performing a purge in a
forward direction through the cooling device 12. For example, a
forward purge may be performed by closing the second and third
valves V2 and V3, opening the fourth valve V4, and opening the
first valve V1 partly. The first valve V1 may supply modest
pressure fluid to the inlet side 12a of the cooling device, and the
fluid may vent from the outlet side 12b of the cooling device via
the fourth valve V4 and the flow rate sensor F to the exhaust port
22. A modest pressure may not generate significant cooling within
the cooling device 12, and so the forward purge may not generate
noticeable or undesirable cooling. The flow rate sensor F may be
used to monitor the state of flow of the fluid, and to detect an
occurrence of a blockage at the orifice 14. Should a blockage be
detected, then the unblock mode 59 may be invoked to try to clear
the blockage before the cooling device 12 may be used.
[0048] Although variable flow control of the first valve V1 may be
preferred, in an alternative form the first valve V1 may be a
straightforward open-closed valve, similar to the other valves
V2-V8.
[0049] It will be appreciated that the present invention,
especially as described in the preferred embodiment, may provide
significant advantages in terms of reducing blockage of a cooling
device, and/or automatically unblocking a blocked cooling device,
and/or automatically detecting fault conditions, and/or simplifying
operation of the cooling device.
[0050] An apparatus may be disclosed herein for supplying a
refrigerant fluid to a cooling device, such as a cryosurgical
probe. The apparatus may include any or all of the following
features: An arrangement of valves may control the supply of fluid
to and from the cooling device. Fluid may flow in a forward
direction through the cooling device for generating cooling by
expansion of the fluid in the cooling device. The apparatus may
execute a programmed sequence of cooling and heating cycles
automatically. Backflushing of the fluid may be used for clearing
contaminants from the inlet side of the cooling device. A pulse
width modulated control signal may be used to control one of the
valves to have a variable effective aperture. A flow rate sensor
may detect the flow rate through the cooling device. The detected
flow rate may be used to detect an occurrence of a blockage and/or
for controlling the fluid supplied to the cooling device. A
blockage may be cleared by automatic backflushing.
[0051] Although certain features of significance may have been
defined herein and/or in the appended claims, the Applicant claims
protection for any novel feature of combination of features
described herein and/or illustrated in the drawings whether or not
emphasis has been placed thereon.
* * * * *