U.S. patent number RE34,432 [Application Number 07/841,433] was granted by the patent office on 1993-11-02 for power control technique for beam-type electrosurgical unit.
This patent grant is currently assigned to Birtcher Medical Systems, Inc.. Invention is credited to Carol Bertrand.
United States Patent |
RE34,432 |
Bertrand |
November 2, 1993 |
Power control technique for beam-type electrosurgical unit
Abstract
An electrosurgical generator in an electrosurgical unit (ESU)
controls the repetition rate and the energy content of bursts of RF
energy delivered to a gas jet supplied by the ESU, in order to
maintain RF leakage current within acceptable limits while still
achieving a sufficient state of ionization in the gas jet to
reliably initiate the conduction of arcs to the tissue. The
repetition rate of the RF bursts is substantially reduced in an
inactive state when no arcs are delivered. A relatively small
number of the RF bursts delivered during the inactive state have an
increased or boosted energy content to assure an adequate
ionization state in the gas jet.
Inventors: |
Bertrand; Carol (Cambridge,
MA) |
Assignee: |
Birtcher Medical Systems, Inc.
(Irvine, CA)
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Family
ID: |
22840059 |
Appl.
No.: |
07/841,433 |
Filed: |
February 19, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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849950 |
Apr 8, 1986 |
4781175 |
|
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Reissue of: |
224301 |
Jul 26, 1988 |
04901720 |
Feb 20, 1990 |
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Current U.S.
Class: |
606/40;
219/121.54; 219/121.57 |
Current CPC
Class: |
A61B
17/3203 (20130101); A61B 18/042 (20130101); A61B
18/14 (20130101); A61B 18/1233 (20130101); A61B
2018/1213 (20130101); A61B 2018/00761 (20130101); A61B
2018/00886 (20130101) |
Current International
Class: |
A61B
18/00 (20060101); A61B 017/39 () |
Field of
Search: |
;606/37-40
;219/121.54,121.56,121.57 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Dennis et al, "Evaluation of Electrofulguration . . . " Digestive
Diseases & Sciences, vol. 24, No. 11, pp. 843-848, Nov.
1979..
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Primary Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Ley; John R.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation in part of application Ser. No. 849,950,
filed Apr. 8, 1986 for "Electrosurgical Conductive Gas Stream
Technique of Achieving Improved Eschar for Coagulation", now U.S.
Pat. No. .[.4,781,785.]. .Iadd.4,781,175.Iaddend., which is
assigned to the assignee hereof. The disclosure of this previous
application is incorporated herein by this reference.
Claims
What is claimed:
1. In an electrosurgical unit which includes means for conducting a
predetermined gas in a jet to tissue and means for transferring
electrical energy in ionized conductive pathways in the gas jet,
said electrical energy transferring means operatively transferring
arcs to the tissue in the ionized conductive pathways in an active
state to thereby create a predetermined electrosurgical effect on
the tissue, said electrical energy transferring means operatively
creating substantially only ionized conductive pathways in the gas
jet in an inactive state to allow arc initiation upon transition to
the active state, said electrical energy transferring means
including electrosurgical generator means for generating target
bursts of radio frequency electrical energy at a predetermined
inactive repetition rate in the inactive state and for generating
active bursts of radio frequency electrical energy at a
predetermined active repetition rate in the active state, said
electrical energy transferring means applying the bursts of radio
frequency energy to the gas jet, and an improvement to said
electrosurgical generator means comprising, in combination:
repetition rate changing means for changing the predetermined
repetition rate of the target bursts to a value substantially less
than the predetermined repetition rate of the active bursts.
2. An invention as defined in claim 1 wherein said improved
generator means further comprises:
arc sensing means for sensing a condition indicative of the
occurrence of an arc initiation to the tissue in ionized conductive
pathways during the inactive state and for supplying an active
signal upon sensing said initiation .Iadd.condition.Iaddend.; and
wherein:
said repetition rate changing means is responsive to the active
signal for operatively changing the repetition rate from the
inactive rate to the active rate .[.upon receipt of the active
signal.]..
3. An invention as defined in claim 1 wherein said generator means
further comprises:
arc sensing means for sensing a condition indicative of the absence
of at least one arc in the ionized conductive pathways during the
active state and for supplying a target signal upon sensing said
absence .Iadd.condition.Iaddend.; and
said repetition rate changing means is responsive to the target
signal for operatively changing the repetition rate from the active
rate to the inactive rate .[.upon receipt of the target
signal.]..
4. An invention as defined in claim 1 wherein:
the target bursts are generated in a plurality of repeating
sequences during the inactive state, each sequence includes a
plurality of target bursts; and
said generator means further includes booster means for increasing
the energy content of a predetermined plurality .Iadd.of
.Iaddend.less than all of the target bursts occurring during each
sequence, those target bursts of increased energy being booster
target bursts and those other target bursts being normal target
bursts.
5. An invention as defined in claim 1 wherein said improved
generator means further comprises:
arc sensing means for sensing a condition indicative of the
occurrence of an arc initiation to the tissue in the ionized
conductive pathways during the inactive state and for supplying an
active signal upon sensing said initiation
.Iadd.condition.Iaddend., said arc sensing means further sensing a
condition indicative of the absence of at least one arc in the
ionized pathways during the active state and for supplying a target
signal upon sensing said absence .Iadd.condition.Iaddend.; and
said repetition rate changing means is responsive to the active and
target signals for operatively changing the repetition rate from
the inactive rate to the active rate .[.upon.]. .Iadd.in response
to the .Iaddend.receipt of the active signal and for operatively
changing the repetition rate from the active rate to the inactive
rate .[.upon.]. .Iadd.in response to the .Iaddend.receipt of the
target signal.
6. An invention as defined in claim 5 wherein:
the target bursts are generated in a plurality of repeating
sequences during the inactive state, each sequence includes a
plurality of target bursts; and
said generator means further includes booster means for increasing
the energy content of a predetermined plurality .Iadd.of
.Iaddend.less than all of the target bursts occurring during each
sequence, those target bursts of increased energy being booster
target bursts and those other target bursts being normal target
bursts.
7. An invention as defined in claim 6 wherein said generator means
further includes:
temporary disabling means responsive to the target signal for
temporarily disabling the booster means for a predetermined
disabled time period after the target signal is supplied, the
target bursts applied to the gas jet during this predetermined
disabled time period being normal target bursts, said temporary
disabling means further responding to the expiration of the
predetermined disabled time period to thereafter enable said
booster means to commence operating as recited.Iadd., the
predetermined disabled time period being at least the time period
of one sequence of target bursts.Iaddend..
8. An invention as defined in .[.claim.]. .Iadd.claims .Iaddend.2,
5 or 7 wherein:
said .[.means supplies the active signal upon sensing.].
.Iadd.initiation condition is .Iaddend.the first arc to the tissue
occurring while in the inactive state.
9. An invention as defined in claims 3, 5 or 7 wherein:
said .[.arc sensing means supplies the target signal upon
sensing.]. .Iadd.absence condition is .Iaddend.the absence of a
predetermined plurality of consecutive arcs in the active
state.
10. An invention as defined in claim 9 wherein:
said generator means further includes means for establishing a
predetermined active power level of electrical energy to be
delivered to the gas jet in the active state; and
said arc sensing means is also responsive to the predetermined
active power level and operatively supplies the target signal upon
the absence of a relatively fewer predetermined plurality of
consecutive arcs when the predetermined active power level is
relatively higher and supplies the target signal upon the absence
of a relatively greater predetermined plurality of consecutive arcs
when the active power level is relatively lower.
11. An invention as defined in claims 4 or 6 wherein:
the booster target bursts are consecutive in each sequence.
12. An invention as defined in claim 11 wherein the number of
booster target bursts in each sequence is in a range of less than
ten percent of the total number of target bursts in each
sequence.
13. An invention as defined in claims 4 or 6 wherein:
the booster target bursts have an energy content established at
least in part by a .[.peak to peak.]. .Iadd.peak-to-peak
.Iaddend.voltage of at least one cycle of the radio frequency
electrical energy of each booster target bursts; and
the .[.peak to peak.]. .Iadd.peak-to-peak .Iaddend.voltage of at
least one cycle of each booster target burst is substantially
greater than the .[.peak to peak.]. .Iadd.peak-to-peak
.Iaddend.voltage of any cycle of each normal target burst.
14. An invention as defined in claim 7 wherein said generator means
further comprises:
drive pulse generator means for generating driving pulses of energy
having time width durations corresponding to the amount of energy
contained in each pulse, said drive pulse generator means also
generating the driving pulses at repetition rates corresponding to
the repetition rates of the bursts;
drive means receptive of the .[.drive.]. .Iadd.driving
.Iaddend.pulses and operative for creating charging pulses having a
time width related to the .[.drive.]. .Iadd.driving
.Iaddend.pulses;
conversion means receptive of each charging pulse and operative for
converting each charging pulse into one said radio frequency burst,
each burst having an energy content which relates to the energy
content of the corresponding charging pulse which created the
burst; and
pulse width adjusting means connected to said drive pulse generator
means and operative for adjusting the width of driving pulses which
control the charging pulses that established the booster target
bursts and the normal target bursts to achieve the recited energy
characteristics of the target bursts in the active and inactive
states.
15. An invention as defined in claims 1, 4 or 6 wherein said
repetition rate changing means establishes a substantially constant
repetition rate in the inactive state and a different substantially
constant repetition rate in the active state.
16. In an electrosurgical unit which includes means for conducting
a predetermined gas in a jet to tissue and means for transferring
electrical energy in ionized conductive pathways in the gas jet,
said electrical energy transferring means operatively transferring
arcs to the tissue in the ionized conductive pathways in an active
state to thereby create a predetermined electrosurgical effect on
the tissue, said electrical energy transferring means operatively
creating substantially only ionized conductive pathways in the gas
jet in an inactive state to allow arc initiation upon transition to
the active state, said electrical energy transferring means
including electrosurgical generator means for generating target
bursts of radio frequency electrical energy at a predetermined
repetition rate in the inactive state and for generating active
bursts of radio frequency electrical energy at a predetermined
repetition rate in the active state, said electrical energy
transferring means applying the bursts of radio frequency energy to
the gas jet, and an improvement to said electrosurgical generator
means comprising, in combination:
means for generating the target bursts in a plurality of repeating
sequences during the inactive state, each sequence including a
plurality of target bursts; and
booster means for substantially increasing the energy content of a
predetermined plurality .Iadd.of .Iaddend.less than all of the
target bursts occurring during each sequence, those target bursts
of increased energy being booster target bursts and those other
target bursts being normal target bursts.
17. An invention as defined in claim 16 wherein the number of
booster target bursts in each sequence is in a range of less than
ten percent of the total number of target bursts in each
sequence.
18. An invention as defined in claim 17 wherein:
the booster target .[.busts.]. .Iadd.bursts .Iaddend.are
consecutive in each sequence.
19. An invention as defined in claim 17 wherein:
the energy content of the booster target bursts is approximately
three times the energy content of the normal target burst.
20. An invention as defined in claim 19 wherein the number of
target bursts in each sequence is approximately .[.less than.].
five percent of the total number of target bursts in each
sequence.
21. An invention as defined in claim 16 wherein said booster means
further comprises:
means for delaying the application of booster target bursts for a
predetermined time after said generator means transitions from
delivering active bursts to delivering .Iadd.normal .Iaddend.target
bursts. .Iadd.
22. A method of operating an electrosurgical unit for conducting
electrosurgery on tissue, comprising:
conducting a predetermined gas in a jet to tissue;
transferring electrical energy to the gas jet in an active state by
generating active bursts of radio frequency electrical energy
occurring at a predetermined active repetition rate to create arcs
in ionized conductive pathways in the gas jet and to transfer arcs
in the ionized conductive pathways to the tissue for achieving a
predetermined electrosurgical effect on the tissue;
transferring electrical energy to the gas jet in an inactive state
by generating target bursts of radio frequency electrical energy
occurring at a predetermined inactive repetition rate to create
substantially only ionized conductive pathways in the gas jet which
allow arc initiation upon transition to the active state; and
establishing the predetermined inactive repetition rate of the
target bursts at a predetermined value which is substantially less
than the predetermined active repetition rate of the active bursts.
.Iaddend. .Iadd.
23. A method as defined in claim 22 further comprising:
sensing a condition indicative of the occurrence of arc initiation
to the tissue in ionized conductive pathways during the inactive
state; and
terminating the predetermined inactive repetition rate of the
target bursts in response to the sensed initiation condition.
.Iaddend. .Iadd.
24. A method as defined in claim 23 wherein the sensed initiation
condition is the first arc initiated to the tissue in the inactive
state. .Iaddend. .Iadd.25. A method as defined in claim 22 further
comprising:
sensing a condition indicative of the absence of at least one arc
in the ionized conductive pathways during the active state; and
establishing the predetermined inactive repetition rate of the
target bursts in response to the sensed absence condition.
.Iaddend. .Iadd.26. A method as defined in claim 25 wherein the
sensed absence condition is the absence of a predetermined
plurality of consecutive arcs in the active state. .Iaddend.
.Iadd.27. A method as defined in claim 22 further comprising:
sensing a condition indicative of the occurrence of an arc
initiation to the tissue in the ionized conductive pathways during
the inactive state;
establishing the active repetition rate in response to the sensed
initiation condition;
sensing a condition indicative of the absence of at least one arc
in the ionized pathways during the active state; and
establishing the inactive repetition rate in response to the sensed
absence
condition. .Iaddend. .Iadd.28. A method as defined in claim 27
wherein the sensed absence condition is the absence of a
predetermined plurality of consecutive arcs in the active state.
.Iaddend. .Iadd.29. A method as defined in claim 28 wherein the
sensed initiation condition is the first arc initiated to the
tissue during the inactive state. .Iaddend. .Iadd.30. A method as
defined in claim 27 further comprising:
generating target bursts in a plurality of repeating sequences
during the inactive state, each sequence including a plurality of
target bursts; and
increasing the energy content of a predetermined plurality of less
than all of the target bursts occurring during each sequence, those
target bursts of increased energy being booster target bursts and
those other target bursts being normal target bursts. .Iaddend.
.Iadd.31. A method as defined in claim 30 further comprising:
temporarily ceasing the generation of booster target bursts for a
predetermined disabled time period upon sensing the absence
condition, the predetermined disabled time period being at least
the time period of one sequence; and
beginning the generation of booster target bursts after the
expiration of the predetermined disabled time period. .Iaddend.
.Iadd.32. A method as defined in claim 31 wherein the sensed
absence condition is the absence of a predetermined plurality of
consecutive arcs in the active state. .Iaddend. .Iadd.33. A method
as defined in claim 31 further comprising:
sensing a predetermined active power level of electrical energy
delivered to the gas jet in the active state;
establishing the inactive repetition rate in response to sensing
the absence of a relatively fewer predetermined plurality of
consecutive arcs when the predetermined active power level is
relatively higher; and
establishing the inactive repetition rate in response to sensing
the absence of a relatively greater predetermined plurality of
consecutive arcs when the predetermined active power level is
relatively lower.
.Iaddend. .Iadd.34. A method as defined in claim 33 further
comprising:
consecutively generating the booster target bursts in each
sequence. .Iaddend. .Iadd.35. A method as defined in claim 34
further comprising:
generating a number of booster target bursts in each sequence in a
range of less than ten percent of the total number of target bursts
in each sequence. .Iaddend. .Iadd.36. A method as defined in claim
27 further comprising:
generating target bursts in a plurality of repeating sequences
during the inactive state, each sequence including a plurality of
target bursts; and
increasing the energy content of a predetermined plurality of less
than all of the target bursts occurring during each sequence, those
target bursts of increased energy being booster target bursts and
those other target
bursts being normal target bursts. .Iaddend. .Iadd.37. A method as
defined in claim 36 further comprising:
sensing a condition indicative of the absence of at least one arc
in the ionized conductive pathways during the active state;
temporarily ceasing the generation of booster target bursts for a
predetermined disabled time period upon sensing the absence
condition, the predetermined disabled time period being at least
the time period of one sequence; and
beginning the generation of booster target bursts after the
expiration of the predetermined disabled time period. .Iaddend.
.Iadd.38. A method as defined in claim 37 wherein the sensed
absence condition is the absence of a predetermined plurality of
consecutive arcs in the active state. .Iaddend. .Iadd.39. A method
as defined in claim 37 further comprising:
sensing a predetermined active power level of electrical energy
delivered to the gas jet in the active state;
establishing the inactive repetition rate in response to sensing
the absence of a relatively fewer predetermined plurality of
consecutive arcs when the predetermined active power level is
relatively higher; and
establishing the inactive repetition rate in response to sensing
the absence of a relatively greater predetermined plurality of
consecutive arcs when the predetermined active power level is
relatively lower. .Iaddend. .Iadd.40. A method as defined in claim
36 further comprising:
generating a number of booster target bursts in each sequence in a
range of less than ten percent of the total number of target bursts
in each
sequence. .Iaddend. .Iadd.41. A method as defined in claim 36
further comprising:
generating a number of booster target bursts in each sequence at
approximately five percent of the total number of target bursts in
each sequence; and
increasing the energy content of the booster target bursts to a
value approximately three times greater than the energy content of
the normal target bursts. .Iaddend. .Iadd.42. A method of operating
an electrosurgical unit for conducting electrosurgery on tissue,
comprising:
conducting a predetermined gas in a jet to tissue;
transferring electrical energy to the gas jet in an active state by
generating active bursts of radio frequency electrical energy
occurring at a predetermined active repetition rate to create the
arcs in ionized conductive pathways in the gas jet and to transfer
arcs in the ionized conductive pathways to the tissue for achieving
a predetermined electrosurgical effect on the tissue;
transferring electrical energy to the gas jet in an inactive state
by generating target bursts of radio frequency electrical energy
occurring at a predetermined inactive repetition rate to create
substantially only ionized conductive pathways in the gas jet which
allow arc initiation upon transition to the active state, the
target bursts occurring in a plurality of repeating sequences and
each sequence including a plurality of target bursts; and
increasing the energy content of a predetermined plurality of less
than all of the target bursts occurring during each sequence, those
target bursts of increased energy being booster target bursts and
those other target bursts being normal target bursts. .Iaddend.
.Iadd.43. A method as defined in claim 42 further comprising:
generating a number of booster target bursts in each sequence in a
range of less than ten percent of the total number of target bursts
in each sequence. .Iaddend. .Iadd.44. A method as defined in claim
43 further comprising:
consecutively generating the booster target bursts in each
sequence. .Iaddend. .Iadd.45. A method as defined in claim 43
further comprising:
increasing the energy content of the booster target bursts to a
value approximately three times greater than the energy content of
the normal target bursts. .Iaddend. .Iadd.46. A method as defined
in claim 45 further comprising:
generating a number of booster target bursts in each sequence at
approximately five percent of the total number of target bursts in
each sequence. .Iaddend. .Iadd.47. A method as defined in claim 42
further comprising:
delaying the generation of booster target bursts for a
predetermined time after ceasing the delivery of active bursts and
commencing the delivery of
normal target bursts. .Iaddend. .Iadd.48. An electrosurgical
generator for an electrosurgical unit which includes means for
conducting a predetermined gas in a jet to tissue and means for
transferring arcs of electrical energy in ionized conductive
pathways in the gas jet in an active state to create a
predetermined electrosurgical effect on the tissue, the arcs in the
active state resulting from bursts of radio frequency electrical
energy occurring at a predetermined active repetition rate; said
electrosurgical generator comprising:
burst generator means operative during an inactive state for
generating bursts of radio frequency electrical energy to create
substantially only ionized conductive pathways in the gas jet to
allow arc initiation in the gas jet upon transition from the
inactive state to the active state, the inactive state occurring
other than during the occurrence of the active state; and
repetition rate establishing means for controlling the burst
generator means to establish a repetition rate of the bursts in the
inactive state which is substantially less than the predetermined
repetition rate of the
bursts during the active state. .Iaddend. .Iadd.49. An
electrosurgical generator as defined in claim 48 further
comprising:
arc sensing means for sensing a condition indicative of the
occurrence of an arc initiation to the tissue in ionized conductive
pathways during the inactive state and for supplying an active
signal upon sensing said initiation condition; and wherein:
said repetition rate establishing means is responsive to the active
signal for operatively terminating the predetermined inactive
repetition rate. .Iaddend. .Iadd.50. An electrosurgical generator
as defined in claim 49 wherein:
said initiation condition is the first arc to the tissue occurring
while in the inactive state. .Iaddend. .Iadd.51. An electrosurgical
generator as defined in claim 48 further comprising:
arc sensing means for sensing a condition indicative of the absence
of at least one arc in the ionized conductive pathways during the
active state and for supplying a target signal upon sensing said
absence condition; and
said repetition rate establishing means is responsive to the target
signal for establishing the predetermined inactive repetition rate.
.Iaddend.
.Iadd.52. An electrosurgical generator as defined in claim 51
wherein:
said absence condition is the absence of a predetermined plurality
of consecutive arcs in the active state. .Iaddend. .Iadd.53. An
electrosurgical generator as defined in claim 48 further
comprising:
arc sensing means for sensing a condition indicative of the
occurrence of an arc initiation to the tissue in the ionized
conductive pathways during the inactive state and for supplying an
active signal upon sensing said initiation condition, and further
sensing a condition indicative of the absence of at least one arc
in the ionized pathways during the active state and for supplying a
target signal upon sensing said absence condition; and
said repetition rate establishing means is responsive to the active
and target signals for operatively terminating the predetermined
inactive repetition rate in response to the active signal and for
operatively establishing the predetermined inactive repetition rate
in response to the target signal. .Iaddend. .Iadd.54. An
electrosurgical generator as defined in claim 53 wherein:
said absence condition is the absence of a predetermined plurality
of
consecutive arcs in the active state. .Iaddend. .Iadd.55. An
electrosurgical generator as defined in claim 54 wherein:
said initiation condition is the first arc to the tissue occurring
while in the inactive state. .Iaddend. .Iadd.56. An electrosurgical
generator as defined in claim 53 wherein:
said burst generator means generates target bursts in a plurality
of repeating sequences during the inactive state, each sequence
includes a plurality of target bursts; and said burst generator
means further includes:
booster means for increasing the energy content of a predetermined
plurality of less than all of the target bursts occurring during
each sequence, those target bursts of increased energy being
booster target bursts and those other target bursts being normal
target bursts. .Iaddend. .Iadd.57. An electrosurgical generator as
defined in claim 56 wherein said burst generator means further
includes:
temporary disabling means responsive to the target signal for
temporarily disabling the booster means for a predetermined
disabled time period after the target signal is supplied, the
predetermined disabled time period being at least the time period
of one sequence of target bursts; and
reenabling means responsive to the expiration of the predetermined
disabled time period for thereafter enabling said booster means to
commence
operating as recited. .Iaddend. .Iadd.58. An electrosurgical
generator as defined in claim 57 wherein:
said absence condition is the absence of a predetermined plurality
of consecutive arcs in the active state. .Iaddend. .Iadd.59. An
electrosurgical generator as defined in claim 57 wherein:
said arc sensing means is further responsive to a predetermined
active power level of electrical energy delivered to the gas jet in
the active state and operatively supplies the target signal upon
the absence of a relatively fewer predetermined plurality of
consecutive arcs when the predetermined active power level is
relatively higher and supplies the target signal upon the absence
of a relatively greater predetermined plurality of consecutive arcs
when the active power level is relatively lower. .Iaddend.
.Iadd.60. An electrosurgical generator as defined in claim 59
wherein:
the booster target bursts are consecutive in each sequence.
.Iaddend. .Iadd.61. An electrosurgical generator as defined in
claim 60 wherein the number of booster target bursts in each
sequence is in a range of less than ten percent of the total number
of target bursts in each sequence. .Iaddend. .Iadd.62. An
electrosurgical generator as defined in claim 48 wherein:
the burst generator means generates target bursts in a plurality of
repeating sequences during the inactive state, each sequence
includes a plurality of target bursts; and said target burst
generator means further includes:
booster means for increasing the energy content of a predetermined
plurality of less than all of the target bursts occurring during
each sequence, those target bursts of increased energy being
booster target bursts and those other target bursts being normal
target bursts. .Iaddend. .Iadd.63. An electrosurgical generator as
defined in claim 62 further comprising:
arc sensing means for sensing a condition indicative of the absence
of at least one arc in the ionized conductive pathways during the
active state and for supplying a target signal upon sensing said
absence condition; and wherein said burst generator means further
includes:
temporary disabling means responsive to the target signal for
temporarily disabling the booster means for a predetermined
disabled time period after the target signal is supplied upon
sensing the absence condition, the predetermined disabled time
period being at least the time period of one sequence; and
reenabling means responsive to the expiration of the predetermined
disabled time period for thereafter enabling said booster means to
commence operating as recited. .Iaddend. .Iadd.64. An
electrosurgical generator as defined in claim 63 wherein:
said absence condition is the absence of a predetermined plurality
of consecutive arcs in the active state. .Iaddend. .Iadd.65. An
electrosurgical generator as defined in claim 63 wherein:
said arc sensing means is further responsive to a predetermined
active power level of electrical energy delivered to the gas jet in
the active state and operatively supplies the target signal upon
the absence of a relatively fewer predetermined plurality of
consecutive arcs when the predetermined active power level is
relatively higher and supplies the target signal upon the absence
of a relatively greater predetermined plurality of consecutive arcs
when the active power level is relatively lower. .Iaddend.
.Iadd.66. An electrosurgical generator for an electrosurgical unit
which includes means for conducting a predetermined gas in a jet to
tissue and means for transferring arcs of electrical energy in
ionized conductive pathways in the gas jet in an active state to
create a predetermined electrosurgical effect on the tissue, the
arcs in the active state resulting from bursts of radio frequency
electrical energy occurring at a predetermined active repetition
rate; said electrosurgical generator comprising:
burst generator means for generating a plurality of repeating
sequences of bursts of radio frequency electrical energy during an
inactive state to create substantially only ionized conductive
pathways in the gas jet to allow arc initiation in the gas jet upon
transition from the inactive state to the active state, each
sequence including a plurality of bursts; and
booster means for increasing the energy content of a predetermined
plurality of less than all of the bursts occurring during each
sequence in the inactive state, those bursts of increased energy
during the inactive state being booster target bursts and those
other bursts being normal target bursts. .Iaddend. .Iadd.67. An
electrosurgical generator as defined in claim 66 wherein the number
of booster target bursts in each sequence is in a range of less
than ten percent of the total number of target bursts in each
sequence. .Iaddend. .Iadd.68. An electrosurgical generator as
defined in claim 67 wherein:
the booster target bursts are consecutive in each sequence.
.Iaddend.
.Iadd.9. An electrosurgical generator as defined in claim 67
wherein:
the energy content of the booster target bursts is approximately
three times the energy content of the normal target bursts.
.Iaddend. .Iadd.70. An electrosurgical generator as defined in
claim 69 wherein the number of booster bursts in each sequence is
approximately five percent of the total number of bursts in each
sequence. .Iaddend. .Iadd.71. An electrosurgical generator as
defined in claim 66 wherein said booster means further
comprises:
means for delaying the application of booster target bursts for a
predetermined time after the transition from the delivery of active
bursts to the delivery of normal target bursts. .Iaddend.
Description
BACKGROUND OF THE INVENTION
A concern regarding radio frequency (RF) leakage current is present
in any electrosurgical unit (ESU). RF leakage current refers to the
small, but nevertheless sometimes significant, current which flows
into the surrounding environment from the active electrode and the
conductor which supplies the active electrode, when the surgeon has
activated or "keyed" the ESU prior to bringing the active electrode
into operative arcing distance from the tissue of the patient.
There is a concern that the RF leakage current will flow to the
surgeon and to those in the operating room, exposing the surgeon
and others to risk of injury. Based on these concerns, and on
safety regulations, the maximum allowable amount of RF leakage
current which can flow from an ESU must be controlled and
limited.
The RF leakage current is at its maximum during open-circuit,
full-power operating conditions. When the ESU is keyed, but no arcs
travel from the active electrode to the tissue, relatively high
peak-to-peak voltages of full power cause the RF leakage current to
more readily disperse into the surroundings. As soon as the active
electrode is brought into operative distance from the tissue, and
arcs are conducted to the tissue, the circuit is closed, the output
voltage drops under this "loaded" condition, and the RF leakage
current is no longer of a major concern because most or all of the
power is delivered to the tissue. As soon as the conductive
pathways are established to the tissue, .[.RD.]. .Iadd.RF
.Iaddend.leakage current is minimized due to the considerably lower
impedance path of the ionized pathways in the gas jet to the
tissue. The same concern with RF leakage current also occurs after
the active electrode is pulled away an inoperative distance from
the tissue, but the ESU remains keyed.
Beam-type ESUs have special power requirements which other types of
ESUs do not have. A beam-type ESU is one which delivers electrical
energy, usually arcs, in ionized conductive pathways established in
a continuously flowing jet of a predetermined gas. U.S. Pat. No.
4,781,175 (Ser. No. 849,950) discloses a beam-type ESU. In a
beam-type ESU, the gas flowing past the active electrode must be
maintained in an ionized state. The ionized state allows the arcs
to be reliably initiated from the active electrode through the gas
jet to the tissue, when the pencil-like device which delivers the
gas jet and contains the active electrode is brought into an
operative distance with the tissue. Without maintaining a state of
sufficient ionization, arcs will not initiate when the surgeon
desires, or the initiation will not be as reliable and predictable
as is desired. Maintaining the ionization state in beam-type ESUs
can be difficult, because the continuous flow of gas past the
electrode requires electrical energy to be continually delivered in
substantial magnitudes to prevent the ionized state from
extinguishing.
In a conventional ESU, gas is not constantly flowing past the
active electrode. Furthermore, many conventional ESUs require
actual physical contact or near physical contact of the active
electrode with the tissue in order to initiate the arcs. Physical
contact of the active electrode to the tissue is not desirable or
possible in beam-type ESUs. Therefore, the constant state of
ionization in the gas jet flowing from the active electrode must
not only be maintained, but it must be maintained to a degree which
allows the predictable initiation of arcs in the conductive
pathways established by the ionization, once the active electrode
is brought into operative proximity with the tissue.
It has been determined that an effective technique of maintaining
an ionized state of ionized conductive pathways in a gas is to
apply relatively high peak-to-peak voltage to the gas. However,
maintaining the ionization state in the gas jet of a beam-type ESU
by applying a relatively high peak-to-peak voltage has the
detrimental effect of increasing the RF leakage current. Thus, the
requirement to maintain an effective ionized state in the gas jet
sufficient to reliably initiate arcs to the tissue when desired,
and the requirement to limit the amount of RF leakage current, are
both significant but contradictory considerations in beam-type
ESUs.
SUMMARY OF THE INVENTION
The present invention offers the capability of sustaining .[.and.].
.Iadd.an .Iaddend.effectively ionized state of ionized conductive
pathways in a gas jet of a beam-type ESU, to reliably and
predictably initiate the conduction of arcs in the ionized
conductive pathways when the surgeon so desires, but while doing
so, limiting the RF leakage current to an acceptable level.
In accordance with the major aspects of the present invention, an
electrosurgical generator means of the beam-type ESU generates
bursts of radio frequency electrical energy at a predetermined
repetition rate and applies those bursts to the gas jet. In an
inactive operational state, when it is desired to maintain the
ionized state in the gas jet without initiating or conducting arcs
of electrical energy to the tissue, the generator means generates
target bursts of RF electrical energy. In an active operational
state when it is desired to transfer arcs in the ionized conductive
pathways to the tissue, the generator means generates active bursts
of RF electrical energy. The improved features of the present
invention .[.relates to.]. .Iadd.also relate to establishing or
.Iaddend.changing the predetermined repetition rate of the target
bursts to a value substantially less than the predetermined
repetition rate of the active bursts; and during a sequence of
generating a plurality of target bursts, substantially increasing
the energy content of a predetermined plurality of less than all of
the target bursts occurring in each sequence. The target bursts of
increased energy during each sequence, known as booster target
bursts, are relatively few, for example, less than ten percent. The
peak-to-peak voltage of these booster target bursts is
substantially higher than the voltage of the normal target bursts.
The booster target bursts .[.ten.]. .Iadd.tend .Iaddend.to create
the ionized conductive pathways, while the normal target bursts
tend to sustain the ionized conductive pathways between the
application of the booster target bursts.
By repeating the sequences of target bursts in the manner provided,
the ionized state is effectively maintained within the gas jet. By
reducing the repetition rate at which the target bursts are
generated during the inactive state, the amount of RF leakage
current is maintained within acceptable limits because the amount
of energy delivered to the gas jet during a predetermined time
period is reduced. Thus, the present invention limits the RF
leakage current to an acceptable level while maintaining an
effective ionized state in the gas jet to initiate arcs of
electrical energy to the tissue when desired.
Because the reduced repetition rate of the target bursts may be
sufficiently low to cause muscle stimulation, .[.the generator
means also includes improved means for sensing.]. a condition
indicative of the occurrence of arc initiation to the tissue during
the inactive state .Iadd.is sensed.Iaddend., and thereupon
.[.operatively changing.]. the repetition rate .Iadd.is changed
.Iaddend.from the lower inactive rate to the higher active rate
upon sensing such a condition. As .[.soon as.]. arc initiation
occurs, preferably upon occurrence of the first arc to the tissue
in the inactive state, the .[.generator means immediately begins
supplying their.]. higher active repetition rate .Iadd.is supplied
.Iaddend.to avoid significant muscle stimulation. In this manner,
.[.the generator means automatically and rapidly.]. transitions
from the inactive state to the active state .Iadd.occur
automatically.Iaddend..
Similarly, .[.an effective means for terminating.]. the delivery of
RF bursts in the active rate is .[.achieved.]. .Iadd.terminated
.Iaddend.by sensing the absence of at least one arc in the ionized
conductive pathway to the tissue in the active state. Preferably, a
predetermined plurality of absences of arcs are sensed before
transitioning from the active state to the inactive state. The
number of arc absences which occur before transitioning occurs is
preferably related to the amount of power delivered during the
active state. With a higher amount of active power delivered, a
fewer number of arc absences must occur in the conductive pathway
before transitioning from the higher active repetition rate to the
lower inactive repetition rate. Conversely, with lower amount of
active power delivered in the active state, more arc absences are
required before .[.the generator means transitions.]. .Iadd.the
transition .Iaddend.from the higher active repetition rate to the
lower inactive repetition state .Iadd.occurs.Iaddend..
Because the gas jet is in a highly ionized state immediately after
switching from the active to the inactive state, and because the
application of the booster target .[.pulses.]. .Iadd.bursts
.Iaddend.immediately after transitioning from the active to the
inactive state might result in undesired arcing in the inactive
state, .[.the generator means includes means for temporarily
delivering.]. only normal target bursts .Iadd.are delivered
.Iaddend.for a predetermined time period after transitioning from
the active to the inactive states. During this predetermined time
period no booster target bursts are delivered. If the surgeon
desires to immediately recommence the active state, a sufficient
amount of ionization exists as a residual from the active bursts
and the normal target bursts so that arc initiation can immediately
and reliably occur. However, if the surgeon ceases active operation
for more than the predetermined time period, for example three
seconds, the booster target pulses will again commence in the
sequences, to establish a sufficiently ionized state to readily
support arc initiation.
Other significant advantages and improvements are available from
the present invention. A more complete explanation of the details
of the present invention is found in the following detailed
description, taken in conjunction with the accompanying drawings.
The actual scope of the present invention is defined by the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a generalized illustration of a beam-type electrosurgical
unit (ESU) embodying the present invention, illustrating an
electrosurgical generator means (ESG), a gas delivery apparatus, a
handpiece or pencil, and a segment of patient tissue.
FIG. 2 is a generalized block diagram of the ESG and gas delivery
apparatus shown in FIG. 1.
FIG. 3 is a generalized block diagram of the RF logic and arc sense
circuit illustrated in FIG. 2.
FIG. 4 is a generalized schematic diagram of the resonant output
circuit shown in FIG. 2.
FIG. 5 is a generalized schematic and logic diagram of the
repetition rate generator and the pulse generator shown in FIG.
3.
FIGS. 6A, 6B, 6C, 6D, 6E, 6F and 6G are waveform diagrams
illustrating the operation of the circuit elements shown in FIG.
5.
FIG. 7 is a generalized schematic and logic diagram of the arc
sensing circuit and the arc sense logic shown in FIG. 3.
FIGS. 8A, 8B, 8C, 8D, 8E and 8F are waveform diagrams illustrating
the operation of the circuit elements shown in FIG. 7 and the
resonant output circuit shown in FIG. 4.
FIG. 9 is a generalized schematic and logic diagram of the booster
generator shown in FIG. 3.
FIG. 10 is a generalized schematic and logic diagram of the pulse
width reference circuit, the ramp generator, and the RF drive pulse
generator shown in FIG. 3.
DETAILED DESCRIPTION
A beam-type electrosurgical unit (ESU) which embodies the present
invention is illustrated generally in FIG. 1 and is referenced 40.
The ESU 40 includes three major components, a pencil or handpiece
42 which is manipulated by the surgeon, gas delivery apparatus 44
and an electrosurgical generator means (ESG) 46. A flexible cord 48
connects the gas delivery apparatus 44 and the ESG 46 to the pencil
42. The gas delivery apparatus delivers a predetermined gas through
a plurality of individual passageways or lumens 50 in the cord 48
to the pencil 42. The gas issues from a nozzle 52 of the pencil 42
in a directed or substantially laminar flow stream jet 54. The ESG
46 supplies electrical energy over a conductor 56 of the cord 48 to
the pencil. The conductor 56 is electrically connected in the
pencil to a needle-like electrode 58 which extends into the nozzle
52. The electrical energy supplied by the ESG 46 is of a
predetermined characteristic, as discussed in greater detail below,
which is sufficient to ionize the gas flowing through the nozzle 52
and to create ionized conductive pathways in the jet 54. The gas
delivery apparatus 44, the cord 48 and the pencil .[.52.]. .Iadd.42
.Iaddend.are one example of means for conducting a predetermined
gas in a jet. The ESG 46, the cord 48 and the electrode 58 are one
example of means for transferring electrical energy in ionized
conductive pathways in the gas jet.
In an active state or mode of operation of the ESU 40, electrical
energy is transferred in the ionized conductive pathways in the jet
54 in the form of arcs 60. The arcs 60 travel within the jet 54
until they reach tissue 62 of the patient at the electrosurgical
site. The electrical energy which is transferred into the tissue 62
creates a predetermined electrosurgical effect, usually an eschar.
Details of the improved eschar available from a beam-type .[.ESG.].
.Iadd.ESU .Iaddend.are more particularly described in the
aforementioned U.S. Pat. No. 4,781,175.
The electrical energy travels through the tissue 62 to the return
electrode or patient plate 70 which contacts the tissue 62. The
patient plate 70 is connected by the return electrical conductor 72
to the ESG 46. A complete electrical circuit is thus established
for conducting current from the ESG 46, to the electrode 58 in
pencil 42, through the jet 54, to and through the tissue 62, to the
patient plate 70, through the return conductor 72 and back to the
ESG 46.
In an .[.active.]. .Iadd.inactive .Iaddend.state or mode of
operation of the ESU 40, an ionized state of ionized conductive
pathways is maintained in the gas jet 54 issuing from the nozzle 52
but no electrical arcs are conducted in the inactive state. The
ionized conductive paths create a corona or glow discharge within
the jet, and the glow discharge or corona is capable of initiating
arc conduction when the surgeon moves the nozzle 52 into operative
proximity with the tissue 62. At this operative proximity, the
ionized conductive pathways to the tissue 62 establish enough of a
closed circuit through the tissue 62, a patient plate 70 and a
return conductor 72, that arcs 60 commence or initiate in the jet
54.
When the surgeon activates or "keys" the ESU 40 for the delivery of
the active level of electrosurgical power to the tissue, it is
important that the ionized state of ionized conductive pathways
within the gas jet is established. When the nozzle 52 is brought
into operative proximity with the tissue 62, the ionized conductive
pathways will commence conducting arcs. Upon occurrence of these
arcs, the ESG 46 will automatically switch or transition from the
inactive state to the active state and commence delivering an
active level of power to the tissue to achieve the predetermined
electrosurgical effect. Without maintaining an ionization state in
the gas jet in the .[.inoperative.]. .Iadd.inactive .Iaddend.state,
it is impossible or extremely difficult to repeatedly and reliably
initiate arcs 60 in the gas jet 54 to transition to the active
state.
In order to achieve the electrosurgical effect, the surgeon must
activate or "key" the .[.ESG.]. .Iadd.ESU.Iaddend.. The inactive
state then occurs wherein the ionized state of ionized conductive
pathways in the gas jet .[.is.]. .Iadd.are .Iaddend.created,
followed by the delivery of at least one arc to the tissue while in
this inactive state due to the surgeon moving the pencil into an
operative distance from the tissue, followed by an automatic
transition to the active state where the full .[.request.].
.Iadd.requested .Iaddend.amount of electrosurgical power is
delivered to the gas jet and conducted to the tissue.
Details of an exemplary gas delivery apparatus 44 are described in
the above mentioned U.S. Pat. No. 4,781,175. Details of two types
of handpieces or pencils 42 and cords 48 and associated equipment
are disclosed in United States patent .Iadd.application
.Iaddend.Ser. No. 849,950 and in the U.S. patent application Ser.
No. 224,485, for Electrosurgical Conductive Gas Stream Equipment,
filed July 26, 1988. Additional details regarding the ESG 46 are
also disclosed in U.S. Pat. .Iadd.application .Iaddend.Ser. No.
849,950.
.Iadd.The ESG 46, like the ESG described in U.S. Pat. No.
4,781,175, operates in an active operational state during which
arcs of electrical energy are transferred in the ionized conductive
pathways to the tissue to create a predetermined electrosurgical
effect, such as the improved eschar described in U.S. Pat. No.
4,781,175, and also operates in an inactive operational state to
sustain or maintain an ionized state of ionized conductive pathways
to the tissue. The ionized conductive pathways in the inactive
state allow initiation of the arc conduction upon a transition to
the active state from the inactive state. The active state of
operation of the ESG is essentially the similar to that of a
conventional electrosurgical generator such as is disclosed in U.S.
Pat. No. 4,429,694 as described in U.S. Pat. No. 4,781,175.
The inactive state of operation of the ESG 46 delivers the bursts
of radio frequency energy to maintain the sustain the ionized
conductive pathways in the gas jet. In the ESG 46, booster bursts
and normal bursts are preferably delivered to sustain the
ionization, and the booster bursts have a higher energy content
than the normal bursts. A predetermined repetition rate of the
bursts in the inactive state is established at a rate which is
substantially less than the predetermined repetition rate of the
active bursts in the active operational state. The functionality of
the ESG 46 in the inactive operational state is in addition to the
conventional functionality of the ESG in the active operational
state. It is advantageous and preferable to combine the components
of the ESG which operate in the inactive and active operational
states into the single ESG 46 described. .Iaddend.
The major elements of an ESG 46 incorporating the present invention
are illustrated in FIG. 2. A control switch 80 supplies signals to
a front panel control and mode logic microprocessor circuit 82. The
switch 80 controls the circuit 82 to signal the gas delivery
apparatus 44 to initiate the delivery of the gas to the pencil. The
switch 80 also controls the circuit 82 to signal a power supply 84
and a RF logic and arc sense circuit 86 to initiate the application
of electrical energy to the gas jet.
The front panel control and mode logic microprocessor circuit 82
includes a microprocessor and various control devices, such as
switches and potentiometers, which establish the selected flow rate
of the gas delivered from the pencil, the source of gas to be
delivered (when more than one predetermined type of gas is
available), and a variety of other electrical control and operating
signals, as is more fully disclosed in U.S. Pat. Ser. No. 849,950.
The signals which are supplied to the RF logic and arc sense
circuit 86 include a system clock signal at 88 which is derived
from a microprocessor of the circuit 82, mode control and jam input
count signals supplied over a data path 90 from the microprocessor
to control the operation of the ESG in accordance with the type of
procedure selected by the surgeon (fulguration being the primary
mode relevant to this invention), an active power level analog
signal at 92 which relates to the amount of electrical power
selected by the surgeon for application to the tissue, and an RF
enable signal at 94 which enables the RF logic and arc sense
circuit 86 to function in the manner described below when
electrical energy is delivered.
Gas- and electrical-related alarm conditions are also protected by
the circuit 82, and the RF enable signal at 94 prevents the
delivery of radio frequency electrical energy to the pencil until
all of the proper operating conditions have been satisfied. A
convention followed throughout this description is that the signal
and the conductor upon which that signal appears will both be
referenced by the same reference numeral.
The power supply 84 is activated by signals from the circuit 82.
The power supply 84 receives electrical energy from conventional AC
power source 96 and rectifies the AC power to DC power. When
activated, the power supply 84 delivers a predetermined
substantially constant voltage level of DC power to a resonant
output circuit 100. The power supply 84 is conventional.
The RF logic and arc sense circuit 86 delivers drive pulse signals
102 and 104 to the RF drive 98. The drive pulse signal 102
initiates a conduction switching signal 106 from the RF drive 98,
and the drive pulse signal 104 initiates an extinguishing switching
signal 108 from the RF drive 98. The switching signals 106 and 108
switch energy from the power supply 84 to the resonant output
circuit 100. The conduction switching signal 106 starts the flow of
charging current from the power supply 84 to the resonant output
circuit 100. The extinguishing switching signal 108 terminates the
flow of charging current to the resonant output circuit 100. The
amount of energy transferred from the power supply 84 to the output
circuit 100 is determined by the time width between the drive pulse
signals 102 and 104 which respectively control the switching
signals 106 and 108, because the output voltage of the power supply
84 is constant. The resonant output circuit 100 commences
resonating at its natural frequency (RF) after the switching signal
108 extinguishes the flow of charging current from the power supply
84.
The RF drive 98 energizes the resonant output circuit 100 at a
predetermined repetition rate established by the drive signals 102
and 104, and the resonant output circuit 100 discharges at its
resonant frequency by conducting electrical energy to the tissue at
the surgical site. For a constant output impedance, the
peak-to-peak output voltage of the resonant output circuit varies
in direct relation to the width of the charging current pulse
created by the switching signals 106 and 108 which are created by
the drive pulse signals 102 and 104, respectively. Details
regarding the RF drive 98 and resonant output circuit 100 are
disclosed more completely in U.S. Pat. No. 4,429,694 and
.Iadd.patent application .Iaddend.Ser. No. 849,950.
The RF logic and arc sense circuit 86 receives a control signal 110
from the resonant output circuit 100. The control signal 110
relates to the condition of power delivery to the patient tissue,
and is employed primarily to detect .Iadd.or sense .Iaddend.the
presence of arcs in the ionized conductive pathways in the gas jet
to the tissue. The control signal 110 is employed by the RF logic
and arc sense circuit 86 to change the repetition rate of drive
signals 102 and 104 to a higher active repetition rate when
electrosurgery is being performed and to a lower inactive
repetition rate when the ionized state in the gas jet is to be
maintained, so as to readily initiate the conduction of arcs in a
reliable transition to the active state when desired.
When the pencil is not within a predetermined operative distance
from the tissue, the inactive state of electrical power delivery
exists. During the inactive state target bursts of RF energy are
delivered to the gas jet to initiate and sustain ionization. The
target bursts are of two levels: booster target bursts and normal
target bursts. The booster target bursts are of higher energy
content and occur much less frequently than the normal target
bursts. The circuit 86 controls the energy content of the booster
target bursts.
When the pencil is moved into sufficiently-close operative
proximity to the tissue, an arc will travel in the ionized
conductive pathway to the tissue. The control signal 110 from the
resonant output circuit 100 indicates the presence of arcs. The
circuit 86 .[.immediately.]. transitions from the inactive state to
the active state and increases the repetition rate of the signals
102 and 104 from the inactive rate to the active rate when arcs are
sensed in the inactive state.
After the pencil is removed to an inoperative distance from the
tissue, the control signal 110 indicates the absence of arcs in the
ionized conductive pathways to the tissue. The RF drive and arc
sense circuit 86 reduces the repetition rate from the higher .[.arc
sense circuit 86 reduces the repetition rate.]. .Iadd.active rate
to the lower inactive rate after a .Iaddend.predetermined number of
repetitions occur when the absence of arcs is indicated.
Further details of the RF logic and arc sense circuit 86 are
illustrated in FIG. 3. The system clock signal 88 is applied to an
RF logic clock 112 which delivers clock signals 114 to a repetition
rate generator 116 and to a pulse generator 118. Signals from the
data path 90 are also applied to the repetition rate generator 116
and pulse generator 118. The signals from the data path 90 are
derived from the microprocessor of the circuit 82 (FIG. 2) and are
employed by the repetition rate generator 116 to establish the
repetition rates for the active and inactive states or modes of
operation pertinent to this invention. A repetition (rep) signal is
applied at 170 from the repetition rate generator 116 to the pulse
generator 118. The rep signal 170 establishes the repetition rate
at which the pulse generator 118 supplies pulse signals 122. The
width of each pulse signal 122 is established by the signals
supplied by the microprocessor on the data path 90 to the pulse
generator 118.
The control signal 110 from the resonant output circuit 100 (FIG.
2) is supplied to an arc sensing circuit 124. The arc sensing
circuit 124 supplies a signal 126 to an arc sense logic circuit
128. The signal 126 indicates the presence or absence of arcs being
delivered by the resonant output circuit 100 (FIG. 2) to the
tissue. Another input signal to the arc sense logic circuit 128 is
the active power level signal 92. Upon the signal 126 indicating
the absence or presence of a predetermined number of arcs, as
influenced by the level of the active power signal at 92, the arc
sense logic 128 changes the logic level of an active/target signal
130. The active/target signal 130 is applied to the repetition rate
generator 116, to a booster generator 132 and to a pulse width
reference circuit 136. The active/target signal 130 controls the
repetition rate generator 116 to change the repetition rate between
a higher active repetition and a lower inactive repetition rate in
the target state. The booster generator 132 responds to the
active/target signal 130 by generating a booster signal 134 to
periodically increase the energy content of a selected number of
target bursts, called booster target bursts.
The active/target signal 130, the booster signal 134 and the active
power level signal 92 are applied to a pulse width reference
circuit 136. The pulse width reference circuit 136 responds to each
of the three input signals 92, 130 and 134 by supplying a width
control signal 138. A ramp generator 140 receives the pulse signal
122 and the width control signal 138, and generates a modulated
width pulse signal 142. The pulse signal 122 controls the onset of
the modulated width pulse signal 142, and the width control signal
138 controls and modulates the width of the pulse signal 142. An RF
drive pulse generator 144 responds to the pulse signal 122 and the
modulated width pulse signal 142 to create the drive pulse signals
102 and 104. Further details regarding the nature and operation of
each of the elements shown in FIG. 3 are described below.
Details of the resonant output circuit 100 are shown in FIG. 4.
Four high current switches 146 are electrically connected in
series. The application of the conduction switching signal 106
causes all four high current switches 146 to become simultaneously
conductive. The high voltage at terminals 148 and 150 from the
power supply 84 (FIG. 2) charges a resonant LC or "tank" circuit
152 during the time the high current switches 146 are conductive. A
capacitor 154 is part of the tank circuit 152 as well as an output
transformer 156, having a primary winding 158 and a secondary
winding 160. The primary winding 158 is thus charged with high
current electrical energy from conductors 148 and 150 when the high
current switches 146 are simultaneously conductive. When the high
current switches 146 are extinguished or become nonconductive by
the application of the extinguishing switching signal 108, the tank
circuit 152 commences oscillating at its natural RF frequency. The
natural frequency is primarily established by the effective
inductance value of the primary winding 158 and the value of the
capacitor 154. An unloaded natural frequency of approximately
500-600 KHz has proved satisfactory.
Electrical energy is transferred from the tank circuit 152 to the
secondary winding 160 of the output transformer 156 and through
isolating capacitors 164 to the pencil 42 and tissue 62 (FIG. 1).
The impedance created within the pencil, the impedance experienced
by the arcs in the ionized pathways of the gas jet, and the
impedance or resistance of the tissue causes a damping effect on
the electrical energy in the tank circuit 152, establishing a ring
down cycle of RF oscillations. Under loaded conditions, inherent
reactances in the tissue and energy delivery paths modify the
unloaded frequency of the high frequency surgical signal compared
to the natural frequency of the resonant circuit.
Each ring-down cycle of RF oscillations is established by one
charging current pulse to the tank circuit 152. This ring-down
cycle of .[.RD.]. .Iadd.RF .Iaddend.oscillations is referred to as
a "burst" of RF energy. The peak-to-peak voltage of each burst
varies in direct relation to the amount or time width of the
charging current pulse delivered to the tank circuit 152, for a set
output impedance.
.[.The.]. .Iadd.To .Iaddend.replenish the energy in the resonant
circuit 152 after each burst or ring down cycle, the high current
switches 146 are switched on and off during each repetition. These
repetitions occur at a predetermined repetition rate, which is
considerably less than the natural frequency of the tank circuit
152. The time during which the switches 146 are on controls the
amount of energy delivered to the tank circuit 152 and also the
amount of energy delivered during each burst. The resonant output
circuit is thus one example of means for converting the charging
pulses into RF energy bursts.
A sensing transformer 162 is also connected in series in the
resonant circuit 152. The sensing transformer 162 derives the
control signal 110. The control signal 110 represents the
electrical signals in the tank circuit 152, and those conditions
are representative of the arcing condition in the gas jet.
Details regarding the repetition rate generator 116 and the pulse
generator 118 are shown in FIGS. 5 and 6A through 6G. The primary
component of the repetition rate generator 116 is a presettable
synchronous down counter 166. A similar down counter 168 is also
the major component of the pulse generator 118. The down counters
166 and 168 are conventional items, such as those marketed under
the designation CD40103B. The clock signals 114 from the RF logic
clock 112 (FIG. 3) are applied to the clock inputs of both down
counters 166 and 168. The clock signal 114 is illustrated in FIG.
6A. Signals from the data path 90 are applied to some of the jam
input terminals of the down counter 166, and the target/active
signal at 130 is applied to at least one other jam input terminal.
Signals from the data path 90 are also applied to the jam input
terminals of the down counter 168.
The predetermined count value of each presettable down counter is
set by the signals at the jam inputs. A clock signal has the effect
of decrementing the set count upon each positive transition of the
clock input signal. The count which is set by the jam input signals
may be established in one circumstance by the application of a low
level logic signal to the synchronous preset enable (SPE) input
terminal of the down counter.
The down counter 166 is the preferred form of means for
establishing the repetition rate and for changing the repetition
rate at which the drive pulse signals 102 and 104 (FIG. 2) are
delivered to cause charging of the tank circuit 152 of the resonant
output circuit 100 (FIG. 4). During the active state when an active
level of power is delivered to the tissue, the active/target signal
130 is at a high level. The other signals from the data path 90 in
conjunction with the high active/target signal 130, define a
digital input signal which defines the jam input count to the down
counter 166. The clock signals 114 decrement the down counter 166
until the count established by the jam input signals is reached, at
which time the output signal 170 goes low. The signal at 170 is
shown in FIG. 6B. The low signal at 170 is applied to the SPE input
terminals of both down counters 166 and 168. Upon the next positive
edge of a clock signal at 114, the down counters 166 and 168 are
again loaded or jammed according to the counts applied at their jam
input terminals.
The signal 170 establishes the length of each repetition interval
in terms of the number of clock signals 114 which define each
repetition. In the active state, the repetition .[.rate.].
intervals are shorter, resulting in a more frequent repetition
rate. The preferred repetition interval is approximately 32
microseconds in the active state. In the inactive or target state,
the repetition interval is substantially longer, occurring once
each preferred time interval of approximately 56 microseconds. A
lower repetition rate is thus established in the inactive state.
The change in repetition rate is achieved when the active/target
signal 130 changes between its high and low logic levels. A high
level signal 130 changes the jam input value to shorten the
repetition rate, while the low level signal 130 changes the jam
input value to lengthen the repetition rate. Although FIG. 6B only
illustrates the repetition rate established by the signal 170 for
the active state, the inactive or target state would be similar
except that the number of clock cycles 114 would be increased
substantially between each low level portion of the signal 170.
The signal 170 is applied to the pulse generator 118. The count
defined by the jam input signals to the counter 168 is set
immediately after the signal 170 goes low. A NAND gate 172 receives
the signal at 170 at one input terminal, and a signal 174 is
applied to the other input terminal from an inverter 176 which is
connected to the output terminal of the down counter 168. The
signal 174 is illustrated in FIG. 6E. The output signal 180 from
the NAND gate 172 is illustrated in FIG. 6C. The signal at 180 and
the clock signal 114 are applied to the input terminals of another
NAND gate 182 and the output signal 184 from the NAND gate 182 is
shown in FIG. 6D. The signal 184 is applied to the clock input
terminal of the down counter 168.
Upon the occurrence of a signal at 170 which establishes the length
of the repetition interval relative to the clock signals 114, and
hence the repetition rate, the signal 184 provided by the NAND
gates 172 and 182 commences decrementing the down counter 168. The
down counter 168 commences counting the number of clock pulses 114
which will establish the width of the signal 174. The down counter
168 thus becomes a preferred form of a means for generating a
signal by which the pulse signal 122 will ultimately be derived.
The width of the pulse signal 122 is ultimately established by the
count set or jammed into the down counter 168.
The signal 174 is applied to the D input terminal of a flip-flop
186. The clock signal 114 is applied to the clock input terminal of
the flip-flop 186. The output signal 188 from the flip-flop 186 is
shown in FIG. 6F. The signals at 174 and 188 are applied to an OR
gate 190, and the output signal from the OR gate is the pulse
signal 122 which is shown in FIG. 6G. The pulse signal 122 is
somewhat less in time width than the signal at 188, because of the
manner in which the logic elements shown in FIG. 5 are clocked on
the positive edge transitions of the clock signal 114.
Details regarding the arc sensing circuit 124 and the arc sense
logic 128 are illustrated in FIGS. 7 and 8A through 8F. The control
signal 110 from the resonant output circuit 100 (FIGS. 2 and 4) is
applied to the arc sensing circuit 124. This control signal 110 is
illustrated in FIG. 8A. The control signal 110 is applied through
resistors to a Zener diode 192. The Zener diode 192 rectifies the
negative half cycles of the control signal 110 while passing the
positive half cycles, which are limited by the Zener diode
breakdown voltage. The signals passed by the Zener diode 192 are
applied to the noninverting input of a comparator 194. A resistive
network 196 establishes a threshold level 198 which is applied to
the inverting input terminal of the comparator 194. Only those
positive half cycles of the control signal 110 which exceed the
threshold level 198 create output pulses from the comparator 194.
These output pulses are applied to the clock input terminal of a
conventional counter 200. Each positive half cycle of the control
signal 110 which exceeds the threshold level 198 increments the
counter 200.
The counter 200 supplies a high level signal 126 after it has
counted a number of output pulses from the comparator 194 which
correspond to the output terminal from which the signal 126 is
derived. When the counter 200 reaches the predetermined output
count (which is illustrated as three), the signal 126 goes high, as
is shown in FIG. 8C. Thus, the arc sensing circuit 124 supplies the
signal 126 only after a predetermined number of positive half
cycles of the control signal 110 exceed the threshold level
198.
The predetermined number, for example three, is selected to be able
to reliably distinguish an absence of arcs, because, as is
illustrated in FIG. 8A, the non-arcing condition is represented by
a number of oscillations after each charging repetition, while the
arcing condition is represented by a highly damped signal which
does not oscillate above the threshold level 198 for the required
number of times before the signal 126 occurs. Thus, the arc sensing
circuit 124 reliably detects arcing and non-arcing conditions from
the control signal 110 and supplies the signal 126 when a
non-arcing condition is detected. The signal 126 is reset to a low
level at the start of each charging repetition by the application
of the pulse signal 122 to the reset terminal of the counter
200.
The arc sense logic 128 receives the signal 170 from the repetition
rate generator 116 (FIG. 5). The signal 170 occurs once during each
repetition interval. The signal at 170 is illustrated in FIG. 8B.
The signals 170 and 130 are applied to the input terminals of a
NAND gate 204. The signal 170 is applied to an OR gate 206 and NOR
gates 208 and 210. The signal 126 is also applied to OR gate 206.
One input signal to NOR gate 208 is derived from the output signal
from NOR gate 210. Another input signal to NOR gate 210 is derived
from a comparator 212.
The comparator 212 receives the active power level signal 92 at its
noninverting input, and a threshold level signal 214 at its
inverting input. The threshold level signal 214 is established by
the resistive network 215. When the active level power signal 92
exceeds the threshold signal 214, the output signal from the
comparator 212 is high. For example, when the active power level
signal 92 represents a value greater than approximately 85 watts, a
high output signal from the comparator 212 is presented to the
input terminal of the NOR gate 210. The high output signal from the
comparator 212 is used for changing the jam input signals applied
to a presettable down counter 216. The down counter 216 is used to
establish the number of non-arcing repetition intervals which are
allowed to occur prior to switching or transitioning from the
active state to the inactive state. The active/target signal 130
will be held in a high level indicating an active state until a
predetermined number of repetition intervals indicating an absence
of arcs being delivered are sensed.
Preferably, at power levels greater than approximately 85 watts, as
established by the resistive network 215, the active/target signal
130 will transition from the high active level to the low target
level in approximately the preferred number of four consecutive
repetition intervals when no arcs are sensed. When the active power
level is less than 85 watts, the preferred number of consecutive
repetition intervals which occur before transitioning to the low
level active/target signal (indicating an inactive state) is
preferably approximately 128.
When the ESU is first keyed, the down counter 216 is jammed to
start in the inactive level with a low level signal 130 as is shown
in FIG. 8F. The signals 130 and 170 cause the NAND gate 204 to
supply an output signal 218 as is shown in FIG. 8D. The signal 218
forms the clock signal to the down counter 216. During the inactive
state, the signal 218 remains high and therefore does not decrement
the counter 216.
The signals 170 and 126 are applied to the OR gate 206, and an
output signal 220 (shown in FIG. 8E) is applied to the asynchronous
preset enable (APE) terminal of the down counter 216. A low signal
at the APE terminal has the effect of asynchronously jamming the
input count into the down counter 216. With the application of
every signal 170 during the active state when the signal 126 is
low, the down counter 216 is repeatedly jammed with its input count
established by the output signals from the NOR gates 208 and 210.
In the inactive state, when there is a high output signal .[.202.].
.Iadd.126 .Iaddend.from the counter 200, this high output signal is
coupled through the OR gate 206. The high level signal 220 at the
APE input terminal of the down counter 216 prevents it from being
repeatedly jammed to its input count. The signals 218 are thus
allowed to start decrementing the counter 216.
Operation of the arc sensing circuit 124 and the arc sense logic
128 relative to the control signal 110 and the active level power
signal 92 proceeds as follows. Upon the first arcing condition in
the inactive state shown at point 222 in FIG. 8A, the signal 126
from the counter 200 goes low. The absence of the signal 126 to the
OR gate 206 allows the low level transition of signal 170 to create
a momentary low signal at the APE input terminal of the down
counter 216. The input count set by the jam input signals is
thereby set in the down counter 216, and the active/target signal
130 goes high. The high active/target signal 130 allows the signal
218 from the NAND gate 204 to decrement the down counter 216.
However, with each consecutive repetition interval when an arc is
sensed, the signal at 220 continues to jam the input count to the
down counter 216 so that the signals 218 do not effectively
decrement the counter 216 because it is repeatedly rejammed. This
condition continues throughout the active state while an active
level of power is applied to the tissue. As soon as the pencil is
pulled back away from the tissue to a predetermined distance where
each repetition period results in a non-arcing condition, as is
illustrated at points 224 in FIG. 8A, the counter 200 supplies a
high level signal 126. The signal 126 causes the OR gate 206 to
supply a high output signal 220 to the APE terminal, thereby
preventing the resetting of the counter 216. The signal at 218
commences decrementing the counter, and the active/target signal
130 goes to a low level after the counter 216 has been decremented
to the value established by the jam input signals from the NOR
gates 208 and 210.
It is important that the repetition rate is changed from the
inactive rate to the active rate immediately upon the detection of
the first arc to the tissue. This is established by the signal 126
which, while creating the signal 220 to jam the inputs, causes the
active/target signal 130 to immediately assume a high level. By
switching immediately upon the first detected arc, the lower
repetition rate of the inactive rate will have a minimum muscle
stimulation effect. The inactive repetition rate is sufficiently
low that it can create muscle stimulation if the change or
transition to the higher active rate is not immediately
accomplished.
Transition from the active state to the inactive state after a
predetermined number of non-arcing repetition intervals is
important to ensure that the distance at which the arcs in the gas
jet extinguishes is different than the distance at which the arcs
are initiated. The beam is actually a collection of individual arcs
in a uniform bundle. As long as the length of the beam is such that
all arcs terminate on tissue, the control signal 110 will remain
heavily damped. However, as the beam is made longer with respect to
the tissue, occasional arcs in the bundle fail to reach the tissue,
with the result that a lightly damped control .[.signals.].
.Iadd.signal .Iaddend.110 occasionally occurs. Initially, the
lightly damped control signal may occur only once in a large number
of cycles. However, as the beam is made longer, the ratio of
lightly damped to heavily damped responses increases. This reverse
situation occurs when .[.activating the beam.]. .Iadd.transitioning
to the active state.Iaddend.. As the glow discharge created by the
ionized gas jet is brought closer to the tissue, the glow increases
until more and more arcs bridge the gap, resulting in more and more
heavily damped control signals 110.
By immediately switching to the active level of delivered power
upon sensing the first arc, and by not switching from the active
level to the inactive level until a predetermined number of
absences of arcs during sequential repetition intervals are
detected, it is assured that the beam will continue in the active
state even though the surgeon may unintentionally remove the pencil
a short distance out of the operative range while performing the
procedure. Switching to the inactive state from the active state
only after a predetermined number of repetition rates assures that
there will be no fluttering or other instability created by the
unintentional fluctuations in position of the pencil, and also
assures a more reliable and precise initiation and operation.
Details regarding the booster generator 132 are illustrated in FIG.
9. Two presettable down counters 225 and 226 are connected in
series. The active/target signal at 130 is applied to an inverter
227. The inverter 227 supplies an output signal to the clear or
reset (RST) terminals of the down counters 225 and 226. A low input
signal to the RST terminals causes each down counter 225 and 226 to
asynchronously be cleared and reset to its maximum count. This
occurs after a transition of the active/target signal 130 to the
active state, holding the counters 225 and 226 at their maximum
count and therefore disabling them during the active state.
After a transition of the active/target signal 130 to the inactive
state, the counters will have been set for their maximum count
instead of the count normally set at the jam inputs. Since the
counter 226 is normally jammed to a .[.counter.]. .Iadd.count
.Iaddend.of 4, the maximum count represents a substantial increase.
Resetting the counters thus has the effect of delaying the onset of
the booster signal 134, so that the added energy of the booster
target pulses will not immediately cause unintentional arcing in
the inactive state for a predetermined time after the active state
is terminated. This is desirable because the active state has
caused a residual amount of ionization which could easily support a
distracting and potentially undesirable state of fluttering or
intermittent arcing in the inactive state. After the predetermined
time period, the residual ionization has dissipated and the
fluttering condition is not likely to occur. At this point the
booster signals 134 may be delivered. Resetting the counters 225
and 226 is one example of means for temporarily disabling the
booster generator.
When the ESU is first keyed, the counters 225 and 226 will be
jammed to their normal count, as shown in FIG. 9. The counter 225
will commence decrementing based on the pulse signal 122 from the
drive pulse generator 118 (FIG. 3). The pulse signals 122 occur
once each repetition period, so the down counter 225 is decremented
once each repetition period.
The signal 174 is applied to a carry-in (CI) input terminal of the
down counter 225. A high level signal 174 inhibits the counter 225
from counting. Thus, the application of the pulse signal 122 causes
the counter 225 to be decremented only if the CI input terminal of
the counter 225 is low, which will occur when the signal 174 from
the pulse generator 118 (FIG. 5) goes low.
The jam input signals to the counter 225 are set for the maximum
counting capability of the counter 225, which is the number
.[.225.]. .Iadd.255.Iaddend.. Once the counter 225 has been
decremented, a low level output signal is supplied to the CI input
terminal of the down counter 226, to allow it to commence counting.
Down counter 226 decrements by one count, at which point down
counter 225 again commences counting downward from its maximum
count set by its jam inputs. The procedure continues until four
complete cycles of counts from the counter 225 have occurred.
The output signal from the down counter 226 is applied through an
inverter 230 to a NAND gate 231. The other input signal to the NAND
gate 231 is the modulated width pulse signal 142 which occurs at
the end of each drive pulse. Thus, at the end of the drive pulse
which occurs after 1,020 repetition intervals (counted by down
counters 225 and 226) the NAND gate 231 supplies a low signal to
the APE input terminal of a presettable down counter 232. The jam
inputs to the down counter 232 are established for a count of 48.
The low signal at the APE terminal asynchronously forces the count
from the jam inputs into the down counter 232. The output signal
from the down counter 232, which is the booster signal 134, goes
high, and the signals 122 and 134 are logically combined in the
NAND gate 234 for decrementing the counter 232. After the counter
232 has counted down from its jam input count, the booster signal
134 goes low.
The booster generator 132 thus establishes a number of repetition
intervals in a sequence of repetition intervals defined by the
counts of the counters 225, 226 and 232. During this sequence,
which in the form shown amounts to 1020 repetitions, the booster
signal 134 is available to increase the energy content of 48
consecutive repetitions of target bursts. The amount of energy in
these 48 target bursts, known as booster target bursts, is
increased to maintain the ionization in the gas jet, while the
remaining 972 repetitions in each sequence have normal level target
bursts. Usually ten percent or less of the target bursts in a
sequence should be booster target bursts. Preferably this
percentage should be reduced to less than five percent. It has been
found satisfactory to increase the energy content of the booster
target bursts to three times the energy content of the normal
target bursts, when about five percent of the target bursts are
booster target bursts.
The width of the active level pulses, the booster target pulses and
the normal target pulses is derived by the pulse width reference
circuit .[.135.]. .Iadd.136.Iaddend., the ramp generator 140 and
the RF drive pulse generator 144, the details of which are
illustrated in FIG. 10.
The pulse width reference circuit 136 receives the active power
level signal 92 and applies it to a buffer amplifier 236. The
output signal from the amplifier 236 is applied as an analog input
signal to an analog switch 238. The input control signal to the
analog switch 238 is supplied by the active/target level signal
130. With a high level signal 130, the analog switch 238 applies
the analog signal from the buffer amplifier 236 as the width
control signal 138. When the active/target signal 130 is low, an
inverter 240 supplies an input control signal to an analog switch
242. An analog input signal 249 to the analog switch 242 is derived
from a resistive network 246. The control signal from the inverter
240 causes the analog switch 242 to supply the voltage level 249 as
the width control signal 138. The booster signal 134 forms an input
control signal for an analog switch 248. An analog input signal 243
to the analog switch 248 is also derived from the resistive network
246, and the signal 243 is a value greater than the value of the
signal 249. Upon the presence of the booster signal 134, the analog
switch 248 supplies the signal 243 as the pulse width control
signal 138. The output signal from the analog switch 248 is greater
in magnitude than that of the output signal from the analog switch
242. Arranged in this manner, it will be seen from the following
description that the width or energy content of the booster target
pulses is greater than the normal target pulses.
The ramp generator 140 includes a transistor circuit 250 which
charges a capacitor .[.242.]. .Iadd.252 .Iaddend.in a linearly
increasing or ramp fashion once the circuit 250 is triggered by a
pulse signal 122 from the pulse generator 118 (FIG. 3). The
linearly increasing ramp signal is applied to the noninverting
input terminal of a comparator 254. The width control signal 138 is
applied to the inverting input terminal of the comparator 254. When
the ramp signal applied to the noninverting input terminal exceeds
the analog level established by the signal 138, the modulated width
output signal 142 is delivered by the ramp generator 140. The time
.[.width.]. .Iadd.to the occurrence .Iaddend.of the signal 142
created by the ramp generator 140 is determined by the analog level
of the signal 138. Active pulses have a wider time width, because
the output signal from the analog switch 238 will be greater in
analog value. The booster target pulse will have a greater value
than the normal target pulses, since the analog output signal from
the analog switch 248 is greater than that of the analog switch
242. The ramp generator 140 establishes a convenient means for
controlling the width of the drive pulses 102 and 104.
The RF drive pulse generator 144 includes a flip-flop 256 which is
triggered by the pulse signal 122. The flip-flop 256 is reset by
the modulated width pulse signal 142. A transistor circuit 258
includes a transistor 260 which is triggered into conduction by the
output signal from the flip-flop 256. The output drive pulse signal
104 goes to a low level when transistor 260 commences conducting.
When the output signal from the flip-flop 256 .[.cease.].
.Iadd.ceases.Iaddend., transistor 260 becomes nonconductive and
transistor 262 becomes conductive. The drive pulse signal 104 goes
high, and the drive pulse signal 102 goes low, thus terminating the
width of the drive pulse delivered by the RF drive circuit 98 (FIG.
2) to the resonant output circuit 100 (FIG. 2).
The various improvements associated with the present invention have
been described above. The preferred form of the present invention
has been shown and described with a degree of detail. It should be
understood, however, that this detailed description has been made
by way of preferred example, and that the scope of the present
invention is defined by the appended claims.
* * * * *