U.S. patent application number 10/832641 was filed with the patent office on 2004-10-14 for pulsed ultrasonic device and method.
This patent application is currently assigned to Sound Surgical Technologies, LLC. Invention is credited to Cimino, William W..
Application Number | 20040204729 10/832641 |
Document ID | / |
Family ID | 21840148 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040204729 |
Kind Code |
A1 |
Cimino, William W. |
October 14, 2004 |
Pulsed ultrasonic device and method
Abstract
This invention relates to an improved method and apparatus for
generating profiled pulses of ultrasonic frequency vibratory energy
at a distal surface of an ultrasonic applicator of an ultrasonic
surgical instrument for application to tissues of a patient,
including the providing of a profiled pulse signal with a first
profile and a maximum magnitude during a first time portion and a
second profile and a minimum magnitude during a second time
portion, the second time portion being greater than or equal to the
duration of the first time portion, the first time portion being
between one millisecond and fifty milliseconds in duration, and the
maximum magnitude in the range between two and twenty times the
minimum magnitude.
Inventors: |
Cimino, William W.;
(Louisville, CO) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Sound Surgical Technologies,
LLC
Louisville
CO
|
Family ID: |
21840148 |
Appl. No.: |
10/832641 |
Filed: |
April 26, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10832641 |
Apr 26, 2004 |
|
|
|
10027855 |
Dec 21, 2001 |
|
|
|
6726698 |
|
|
|
|
10027855 |
Dec 21, 2001 |
|
|
|
09476879 |
Jan 4, 2000 |
|
|
|
6391042 |
|
|
|
|
09476879 |
Jan 4, 2000 |
|
|
|
09260297 |
Mar 2, 1999 |
|
|
|
6027515 |
|
|
|
|
Current U.S.
Class: |
606/169 ; 604/22;
606/128 |
Current CPC
Class: |
B06B 1/0253 20130101;
A61B 2017/22015 20130101; A61B 2017/320069 20170801; B06B 1/0215
20130101; A61B 17/2202 20130101; A61N 7/02 20130101; A61B
2017/320078 20170801; B06B 2201/76 20130101; A61B 2017/00159
20130101 |
Class at
Publication: |
606/169 ;
604/022; 606/128 |
International
Class: |
A61B 017/32 |
Claims
1. An ultrasonic surgical apparatus for delivery of profiled pulses
of ultrasonic frequency vibratory energy, the ultrasonic surgical
apparatus with a housing to be held and manipulated by a user, an
ultrasonic motor supported within the housing, an ultrasonic
applicator connected to the ultrasonic motor and extending beyond
the housing, the ultrasonic applicator with a distal surface for
engagement with tissues of a patient and, in combination with the
ultrasonic motor, vibratable at a resonant frequency, and the
improvement comprising: a power control circuit electrically
connected to the ultrasonic motor for supplying electrical power to
the ultrasonic motor to produce ultrasonic frequency vibratory
energy that is applied to the ultrasonic applicator; a vibration
monitor circuit electrically connected to the power control circuit
for measuring an electrical vibration signal at the resonant
frequency and proportional to a vibratory amplitude of the
ultrasonic applicator so that the power control circuit supplies
electrical power to the ultrasonic motor at the resonant frequency,
and a profile generator circuit electrically connected to the power
control circuit for producing a profiled pulse signal, the profiled
pulse signal with a first profile and a maximum magnitude during a
first time portion and a second profile and a minimum magnitude
during a second time portion, the second time portion being equal
to or greater than, but no more than three times the duration of
the first time portion, the first time portion between one
millisecond and fifty milliseconds in duration, and the maximum
magnitude in the range between two and twenty times the minimum
magnitude, so that, in combination with the electrical vibration
signal, the power control circuit adjusts the supply of electrical
power to the ultrasonic motor to produce profiled pulses of
ultrasonic frequency vibratory energy.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/476,87 that was filed on Jan. 4, 2000 and
issued as U.S. Pat. No. ______ on ______ which is a continuation of
U.S. patent application Ser. No. 09/260,297 filed on Mar. 2, 1999,
and issued as U.S. Pat. No. 6,027,515 on Feb. 22, 2000.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to ultrasonic surgical
apparatus. More particularly, this invention relates to an improved
method and apparatus for generating profiled pulses of ultrasonic
frequency vibratory energy at a distal surface of an ultrasonic
applicator of an ultrasonic surgical instrument for application to
tissues of a patient with specific relationships between a
magnitude of the pulse of ultrasonic frequency vibratory energy and
a duration of the pulse of ultrasonic frequency vibratory energy so
that the ultrasonic applicator can be driven to vibratory
amplitudes previously not achievable and a more expedient surgical
effect obtained.
[0003] Ultrasonic surgical devices typically operate at frequencies
between 20 kHz and 60 kHz and have application in many surgical
specialties including neurosurgery, general surgery, and ophthalmic
surgery. In general it is known that ultrasonic surgical devices
generate ultrasonic frequency vibratory energy that is applied to
an ultrasonic applicator that vibrates longitudinally and which
contacts the tissues of a patient. The ultrasonic surgical device
may, among other surgical effects, cut, fragment, and/or coagulate
the contacted tissues of the patient.
[0004] Ultrasonic surgical devices are constrained in their ability
to generate ultrasonic frequency vibratory energy due to limits
imposed by machining tolerances and by limits inherent in the
physical characteristics of the materials used to fabricate the
devices. For example, titanium alloys are often used for
fabrication of the ultrasonic applicator that is used to contact
the tissues of a patient. Titanium alloys have inherent fatigue
strength and stress limitations that cannot be exceeded or the
ultrasonic applicator will crack. As a further example, the
ultrasonic motor that converts supplied electrical power to
ultrasonic frequency vibratory energy may be fabricated from
piezoelectric ceramics. Piezoelectric ceramics have inherent
limitations on their ability to efficiently convert electrical
energy to vibratory energy, including limits on applied voltage so
that the ceramic elements do not loose their piezoelectric
properties.
[0005] However, a phenomenon referred to in this disclosure as
`mode coupling`, is most often responsible for establishing the
upper performance bound of an ultrasonic surgical device. Mode
coupling occurs when the vibratory amplitude of an ultrasonic
applicator of an ultrasonic surgical device is increased to such a
level that the ultrasonic frequency vibratory energy at the desired
resonant frequency is coupled to other modes of vibration, referred
to herein as `parasitic modes`. The parasitic modes of vibration
may be at lower frequencies, near-by frequencies, or higher
frequencies, depending of the design of the system. The parasitic
modes of vibration may be longitudinal modes or they may be
transverse modes, or they may be more complicated coupled modes.
Mode coupling is especially troublesome when the ultrasonic
applicator is an elongate probe or catheter with a length greater
than one wavelength at the resonant frequency of the particular
ultrasonic surgical device. Mode coupling may occur for ultrasonic
applicators shorter than one wavelength and may also occur for
ultrasonic applicators that are not shaped like an elongate probe,
for example, flat or convex radiating surfaces.
[0006] The most common type of mode coupling encountered for
ultrasonic surgical devices is the stimulation of a lower or
near-by frequency transverse mode so that the ultrasonic applicator
vibrates in the desired longitudinal vibratory mode and an
undesired transverse vibratory mode simultaneously. This type of
coupled vibration can easily cause stresses in the ultrasonic
applicator material sufficient to break the ultrasonic
applicator.
[0007] Ultrasonic surgical devices that operate at high vibratory
amplitudes also generate undesirable heat, primarily in the
ultrasonic motor, but also in the material of the ultrasonic
applicator due to internal friction and other losses as the
ultrasonic applicator vibrates. If the ultrasonic motor becomes too
hot during a typical procedure then active cooling, such as forced
air or water cooling, of the ultrasonic motor is required, making
the ultrasonic surgical handpiece more expensive and more
cumbersome due to the additional supply lines. If the ultrasonic
applicator becomes hot then the tissues of a patient may be
unnecessarily burned.
[0008] Mode coupling and heat generation have placed fundamental
limits on the performance of ultrasonic surgical systems. What has
been discovered, and is disclosed herein, is an ultrasonic surgical
apparatus and method for generating profiled pulses of ultrasonic
frequency vibratory energy such that mode coupling is suppressed or
eliminated so that the ultrasonic applicator can be driven to
desired vibratory amplitudes which were previously unobtainable,
thus increasing the expediency of a surgical procedure. Further,
because the expediency of the surgical procedure is increased, the
effective dose of ultrasonic frequency vibratory energy delivered
to the tissues of a patient is minimized. Still further, because
the ultrasonic applicator is driven to high vibratory amplitudes
for only short periods of time, internal heating of the ultrasonic
applicator is reduced, as is the electrical power consumed by the
ultrasonic motor.
[0009] The use of switchable or pulsed vibratable tools is
disclosed in patents. U.S. Pat. No. 4,614,178 to Harlt has a dose
meter and a control circuit for switching the mode of operation in
an ultrasonic therapeutic apparatus. A detector circuit is used to
monitor the output to a treatment head so that a time measurement
of the duration of the treatment can be switched between an enabled
or disabled state. This therapeutic, not surgical, device is
intended to deliver heat to the tissues of a patient and the switch
between states of operation is used to ensure that a proper dose of
heat is delivered to the patient,
[0010] U.S. Pat. No. 3,980,906 to Kuris has a driving circuit for
producing bursts of ultrasonic frequency oscillations between 10
kHz and 1,000 kHz at repeated sonic intervals in the range of 10 Hz
to 1,000 Hz, the repeated sonic intervals of ultrasonic frequency
oscillation applied to ultrasonic instruments such as toothbrushes
and razors. This patent uses bursts of ultrasonic energy to reduce
sliding friction for smoother motion when shaving and to provide a
satisfactory tactile sense of operation to a user. Each burst of
ultrasonic mechanical vibration lasts for 1/2 of the sonic
interval, resulting in on-off intervals of equal duration.
[0011] U.S. Pat. No. 4,343,111 to Inoue has an ultrasonic machining
method wherein the vibratory energy is intermittently interrupted
to create a series of time-spaced bursts of vibratory oscillation
and the frequency or amplitude of the vibration is modified during
each of the bursts. This patent uses of bursts of ultrasonic energy
to reduce surface roughness of machined metal parts and to machine
irregular contours into metal pieces.
[0012] U.S. Pat. No. 3,673,475 to Britton has a drive circuit for
generating pulses that are applied to a dental impact tool with a
reciprocating armature. This patent discloses a drive circuit to
generate pulses to `pull-back` and then `drive` an armature, a
technique that is not applicable to ultrasonic frequency vibratable
tools.
[0013] None of the aforementioned patents teaches the use of
profiled pulses of ultrasonic frequency vibratory energy for a
surgical effect on tissues of a patient, none addresses using
profiled pulses of ultrasonic frequency vibratory energy to
suppress or eliminate the phenomenon described herein as mode
coupling, and none suggests using profiled pulses of ultrasonic
frequency vibratory energy to minimize internal heating in the
ultrasonic applicator and the ultrasonic motor. The patents do not
disclose any benefits due to relationships between the magnitude of
the pulses of ultrasonic frequency vibratory energy and the
duration of the pulses of ultrasonic frequency vibratory
energy.
[0014] U.S. Pat. No. 4,827,911 to Broadwin has an ultrasonic
surgical handpiece with a switching means for automatically and
repeatedly switching the amplitude of ultrasonic vibration between
a constant working high amplitude and a constant standby low
amplitude, both used in combination with aspiration and irrigation,
for enhanced fragmentation and improved surgical control. The
invention works by interrupting continuous vibratory operation with
on-off duty cycles, with suitable on-times for first, second,
third, and fourth modes given as 50 milliseconds, 100 milliseconds,
150 milliseconds, and 200 milliseconds, respectively. The
continuous vibratory operation is interrupted with a repetition
rate of at least 30 Hz so that the operator does not distractedly
sense the operation at low amplitude.
[0015] The Broadwin patent does not address or appreciate using
profiled pulses of ultrasonic frequency vibratory energy to
suppress or eliminate the phenomenon described herein as mode
coupling, it does not address using profiled pulses of ultrasonic
frequency vibratory energy to reduce heating in the ultrasonic
applicator and the ultrasonic motor, nor does it disclose any
benefits due to relationships between the magnitude of the pulses
of ultrasonic frequency vibratory energy and the duration of the
pulses of ultrasonic frequency vibratory energy.
OBJECTS OF THE INVENTION
[0016] It is, among other desirable attributes, an overall object
of the present invention to provide a method and apparatus for
delivering profiled pulses of ultrasonic frequency vibratory energy
to an ultrasonic applicator for application to tissues of a patient
with specific durations and magnitudes so that the ultrasonic
applicator can be driven to vibratory amplitudes previously not
achievable, and for a more expedient surgical effect to be
obtained.
[0017] It is a further object of the present invention to provide a
method and apparatus for delivering profiled pulses of ultrasonic
frequency vibratory energy to an ultrasonic applicator for
application to tissues of a patient with specific durations and
magnitudes so that the phenomenon described herein as mode coupling
is reduced., minimized, suppressed, or eliminated.
[0018] It is a still further object of the present invention to
provide a method and apparatus for delivering profiled pulses of
ultrasonic frequency vibratory energy to an ultrasonic applicator
for application to tissues of a patient with specific durations and
magnitudes so that a more expedient surgical effect is obtained,
and therefore, the effective dose of ultrasonic frequency vibratory
energy applied to the tissues of a patient is minimized.
[0019] It is yet still a further object of the present invention to
provide a method and apparatus for delivering profiled pulses of
ultrasonic frequency vibratory energy to an ultrasonic applicator
for application to tissues of a patient with specific durations and
magnitudes so that the electrical power consumed by the ultrasonic
motor is minimized, resulting is a cooler running ultrasonic
motor.
[0020] It is a final object of the present invention to provide a
method and apparatus for delivering profiled pulses of ultrasonic
frequency vibratory energy to an ultrasonic applicator for
application to tissues of a patient with specific durations and
magnitudes so that internal heating of the ultrasonic applicator is
minimized.
SUMMARY OF THE INVENTION
[0021] The apparatus and method disclosed herein are directed
toward achieving the aforementioned objects of the present
invention. It has been learned through experimentation that
previous switching between a constant high vibratory amplitude and
a constant low vibratory amplitude results in mode coupling and the
stimulation of parasitic modes of vibration, fundamentally limiting
the efficient performance of those systems. It has been discovered
that if a first time portion of a pulse ultrasonic frequency
vibratory energy is preferably profiled as described herein and
kept below an upper limit of about fifty milliseconds, and a second
time portion of the pulse of ultrasonic frequency vibratory energy
that follows the first time portion that is at least 3 times the
time duration of the first time portion while the maximum vibratory
amplitude is at least twice but not more than twenty times the
minimum vibratory amplitude, then the mode coupling phenomenon can
be suppressed or eliminated, thus allowing for operation at
vibratory amplitudes previously not achievable. Thus, it is not how
long the ultrasonic frequency vibratory energy is delivered, but
the combination of the magnitude of the pulse of ultrasonic
frequency vibratory energy and the duration and shape of the pulse
of ultrasonic frequency vibratory energy that eliminates mode
coupling, expedites a surgical procedure, minimizes the effective
dose of ultrasonic energy to a patient, and minimizes heat
generation in the ultrasonic motor and the ultrasonic
applicator.
[0022] While the exact reason for successful operation with
profiled pulses of ultrasonic frequency vibratory energy is not
completely understood, the results obtained unequivocally
demonstrate the objects of this invention. It is believed, in
particular, that mode coupling is suppressed using this technique
because there is insufficient time at the highest vibratory
amplitudes to initiate vibration in and couple vibratory energy to
parasitic modes of vibration. Further, it is believed that the
previously unobtainable maximum vibratory amplitudes more
efficiently and more effectively generate a surgical effect in the
tissues of a patient, thus minimizing the effective dose of
ultrasonic frequency vibratory energy required to complete a
surgical procedure. If the first time portion of the pulse of
ultrasonic frequency vibratory energy is less than about one
millisecond mode coupling is suppressed but very little surgical
effect is obtained. Therefore, in general, as the first time
portion of the pulse of ultrasonic frequency vibratory energy is
shortened, an increased maximum magnitude of vibration is required
to achieve and maintain an expedient surgical effect. The
repetitive duty-cycle systems of prior patents failed to appreciate
or recognize the relationship between the magnitude and duration of
pulses of ultrasonic frequency vibratory energy to achieve and
maintain an effective and expedient surgical effect while
eliminating problems due to mode coupling.
[0023] In general an ultrasonic surgical apparatus for delivery of
profiled pulses ultrasonic frequency vibratory energy includes a
housing to be held and manipulated by a user, an ultrasonic motor
supported within the housing, and an ultrasonic applicator
connected to the ultrasonic motor and extending beyond the housing.
Piezoelectric ceramics such as PZT-4 or PZT-8 are the preferred
materials for the ultrasonic motor. The ultrasonic applicator may
be of any shape, including, but not limited to, an elongate solid
probe, and elongate hollow probe, a flat radiating plate, or a
convex radiating lens. The ultrasonic applicator has a distal
surface for engagement with tissues of a patient. The distal
surface may, in the preferred embodiment, be shaped to achieve a
desired surgical effect, including cutting, fragmentation, boring,
and coagulation. The combination of the ultrasonic motor and the
ultrasonic applicator are vibratable at a resonant frequency.
[0024] A power control circuit is electrically connected to the
ultrasonic motor for supplying electrical power to the ultrasonic
motor to produce ultrasonic frequency vibratory energy that is
applied to the ultrasonic applicator to produce vibratory motion in
the ultrasonic applicator.
[0025] A vibration monitor circuit is electrically connected to the
power control circuit for measuring an electrical vibration signal
at the resonant frequency and proportional to a vibratory amplitude
of the ultrasonic applicator so that the power control circuit
supplies electrical power to the ultrasonic motor at the resonant
frequency. The electrical vibration signal may be proportional to a
current or a voltage of the electrical power supplied to the
ultrasonic motor by the power control circuit or it may be
generated by a vibration sensing transducer located in or near the
ultrasonic motor.
[0026] A profile generator circuit is electrically connected to the
power control circuit for producing a profiled pulse signal with a
first profile and a maximum magnitude during a first time portion
and a second profile and a minimum magnitude during a second time
portion. The first time portion is generally the rising portion
plus the time at maximum magnitude of the profiled pulse signal and
the second time portion is generally the falling portion plus the
time at minimum magnitude of the profiled pulse signal. The first
profile is the shape of the leading edge of the profiled pulse
signal as it ascends from the minimum magnitude to the maximum
magnitude. The second profile is the shape of the trailing edge of
the profiled pulse signal as it descends from the maximum magnitude
to the minimum magnitude. The profiled pulse signal, in combination
with the electrical vibration signal, is used in the power control
circuit to adjust the supply of electrical power to the ultrasonic
motor to produce profiled pulses of ultrasonic frequency vibratory
energy.
[0027] To best suppress the phenomenon described herein as mode
coupling and to achieve maximum vibratory performance the first
time portion should be less than fifty milliseconds in duration,
but not less than one millisecond in duration to ensure a
sufficient surgical effect. The preferred range for the first time
portion is between about five milliseconds and about forty
milliseconds. The second time portion should be equal to or greater
than, but no more than three times the duration of the first time
portion. The preferred duration for the second time portion is
approximately the same as the duration of the first time portion.
The maximum magnitude should be in the range between two and twenty
times the minimum magnitude to achieve an expedient surgical
effect. The preferred range for the maximum magnitude is between
four and ten times the minimum magnitude.
[0028] It is preferred that the rising portion of the first profile
and the falling portion of the second profile be monotonically
increasing and decreasing shapes, respectively. Monotonically,
increasing refers to a shape with a continuous rise with time,
without downward dips. Monotonically decreasing refers to a shape
with a continuous fall with time, without upward bumps.
[0029] The preferred range of resonant frequencies for ultrasonic
surgical devices with ultrasonic applicators shaped like elongate
probes, either solid or hollow, is between 20 kHz and 80 kHz. The
preferred range of resonant frequencies for ultrasonic surgical
devices with ultrasonic applicators shaped like a flat radiating
plate or a convex radiating lens is between 80 kHz and 200 kHz.
[0030] A profiled pulse signal may be generated in any time
sequence such that the constraints expressed above are met.
However, it has been found that mode coupling is best suppressed if
a profiled pulse signal is generated not more than twenty times per
second. To minimize the effective dose of ultrasonic vibratory
energy applied to the tissues of a patient it is preferred that the
profiled pulse signal be generated even less often, for example ten
times per second.
[0031] The second time portion of the profiled pulse signal may
vary between consecutive profiled pulse signals. This has the
effect of further reducing mode coupling and the stimulation of
parasitic modes of vibration.
[0032] The preferred ultrasonic surgical apparatus may have an axis
passing through the ultrasonic motor and the ultrasonic applicator.
The ultrasonic motor and the ultrasonic applicator are symmetric
about the axis along which they are disposed for delivery of
ultrasonic frequency vibratory energy in the direction of the
axis.
[0033] A method of using profiled pulses of ultrasonic frequency
vibratory energy to generate an expedient surgical effect and
suppress or eliminate mode coupling is disclosed. The method
includes the steps of engaging a medium, such as tissues of a
patient, with the ultrasonic applicator of the ultrasonic surgical
apparatus, and powering the ultrasonic surgical apparatus with
profiled pulses of ultrasonic frequency vibratory energy, the
profiled pulses with a first profile and a maximum magnitude during
a first time portion and a second profile and a minimum magnitude
during a second time portion, the second time portion being equal
to or greater than, but no more than three times the duration of
the first time portion, the maximum magnitude between two and
twenty times the minimum magnitude, and the first time portion
between one millisecond and fifty milliseconds in duration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The novel features of the invention are set forth in the
appended claims. The invention will be best understood by reference
to the following figures when read in conjunction with the detailed
description of the invention.
[0035] FIG. 1 is a functional block diagram and partial circuit
diagram of an ultrasonic surgical apparatus and circuits for
delivery of profiled pulses of ultrasonic frequency vibratory
energy.
[0036] FIG. 2 is a waveform diagram illustrating the components of
the profiled pulse signal and profiled pulses of ultrasonic
frequency vibratory energy.
[0037] FIG. 3 shows the form of four types of ultrasonic
applicators.
DETAILED DESCRIPTION OF THE INVENTION
[0038] Referring to the drawings, FIG. 1 is a functional block
diagram and partial circuit diagram of an ultrasonic surgical
apparatus 10 and circuits 30 for delivery of profiled pulses of
ultrasonic frequency vibratory energy. The ultrasonic surgical
apparatus 10 includes a housing 11 to be held and manipulated by a
user, an ultrasonic motor 12 supported within the housing 11, and
an ultrasonic applicator 13 connected to the ultrasonic motor 12
and extending beyond the housing 11. In FIG. 1 the ultrasonic
applicator 13 depicted is an elongate probe. The housing 11 may be
fabricated from metals or plastics, the preferred materials are
steam sterilizable plastics such as Delrin (acetal homopolymer) or
Radel (polyphenylsulphone). The ultrasonic motor 12 may be
constructed from piezoelectric ceramics or magnetostrictive metals.
The preferred materials are piezoelectric ceramics such as PZT-4 or
PZT-8. The ultrasonic applicator 13 may be fabricated from metal
materials such as aluminum., stainless steel, or titanium. The
preferred materials for the ultrasonic applicator 13 are titanium
or titanium alloys such as Ti6Al4V. In combination, the ultrasonic
motor 12 and the ultrasonic applicator 13 have a resonant
frequency. The resonant frequency is the frequency of preferred
longitudinal vibration. The ultrasonic applicator 13 has a distal
surface 14 for engagement with tissues of a patient. The distal
surface 14 may be shaped to achieve a desired surgical effect. The
ultrasonic motor 12 and the ultrasonic applicator 13 may be
disposed along and are symmetric about an axis 15.
[0039] A power control circuit 16 is electrically connected to the
ultrasonic motor 12 for supplying electrical power to the
ultrasonic motor 12 to produce ultrasonic frequency vibratory
energy that is applied to the ultrasonic applicator 13 to produce
vibratory motion in the ultrasonic applicator 13. An automatic gain
control element 36 receives an electrical vibration signal from a
vibratory monitor circuit 17 and a profiled pulse signal from a
profile generator circuit 18. The automatic gain control element 36
adjusts the input to a power amplifier 37 so that electrical power
is supplied to the ultrasonic motor 12 through an output
transformer 38 at the resonant frequency to produce profiled pulses
of ultrasonic frequency vibratory energy. A preferred embodiment of
the circuit elements of the automatic gain control element 36 is
shown in the application notes for the Analog Devices 633, an
integrated circuit multiplier, 1992 Analog Devices Special Linear
Reference Manual, pages 2-52,53. In an alternative embodiment, the
automatic gain control element 36 may be replaced with an automatic
phase control element that includes a phase-locked-loop circuit
that maintains a selected phase relationship between the electrical
vibration signal and a reference signal.
[0040] The vibration monitor circuit 17 is electrically connected
to the power control circuit 16 for measuring an electrical
vibration signal at the resonant frequency and proportional to a
vibratory amplitude of the ultrasonic applicator 13. The preferred
electrical vibration signal is proportional to a current of the
electrical power supplied by the power control circuit 16. A
current sense resistor 31 may be located in-line with the primary
of the output transformer 38. The voltage across the current sense
resistor 31 is applied to and amplified by a signal amplifier 32
and the output of the signal amplifier 32 is applied to a band-pass
filter 33. The output of the band-pass filter 33 is the electrical
vibration signal that is in electrical communication with the power
control circuit 16.
[0041] The profile generator circuit 18 is electrically connected
to the power control circuit 16 for producing a profiled pulse
signal. A digital pulse generator 34 generates a pulse signal that
is applied to a low-pass filter 35. The low-pass filter 35 profiles
the leading and trailing edges of the pulse signal generated by the
digital pulse generator 34. The output of the low-pass filter 35 is
the profiled pulse signal that is in electrical communication with
the power control circuit 16.
[0042] A detailed waveform diagram illustrating the components of
the profiled pulse signal and profiled pulses of ultrasonic
frequency vibratory energy is shown in FIG. 2. FIG. 2a shows the
output of the digital pulse generator 34, with a maximum magnitude
20 during a first time portion 21 and a minimum magnitude 22 during
a second time portion 23. To best suppress mode coupling the first
time portion 21 should be in the range between one millisecond and
fifty milliseconds, and the second time portion 23 should be equal
to or greater than, but no more than three times the duration of
the first time portion 21. The preferred duration for the first
time portion 21 is between five milliseconds and forty
milliseconds. For example, if the first time portion 21 is ten
milliseconds then the second time portion 23 must be at least ten
milliseconds, but no more than thirty milliseconds in duration. The
maximum magnitude 20 should be in the range between two and twenty
times the minimum magnitude 22. The preferred range for the maximum
magnitude is between four and ten times the minimum magnitude 22.
For example, if the minimum magnitude 22 has a value of two then
the maximum magnitude must be between four and forty, preferably
between eight and twenty.
[0043] FIG. 2b shows the profiled pulse signal, a result of the
application of the output of the digital pulse generator 34 to the
low-pass filter 35. The profiled pulse signal has a monotonically
increasing shape 24 and a maximum magnitude 20 and a monotonically
decreasing shape 25 and a minimum magnitude 22.
[0044] FIG. 2c shows profiled pulses of ultrasonic frequency
vibratory energy that correspond to application of the profiled
pulse signal, in combination with the electrical vibration signal,
to the power control circuit 16.
[0045] The profiled pulse signal may be generated as a single event
or it may be repeated. To best suppress mode coupling and minimize
heating in the ultrasonic motor and the ultrasonic applicator the
repetition rate should be less than twenty times per second. The
preferred repetition rate is in the range between four and ten
times per second.
[0046] FIG. 3 shows four examples of ultrasonic applicators. The
ultrasonic applicator may be an elongate solid probe as shown in
FIG. 3a, an elongate hollow probe as shown in FIG. 3b, a flat
radiating plate as shown in FIG. 3c, or a convex radiating lens as
shown in FIG. 3d.
[0047] Ultrasonic surgical devices typically operate at frequencies
between 20 kHz and 80 kHz, most specifically when the ultrasonic
applicator is shaped like an elongate solid or hollow probe. When
the ultrasonic applicator is shaped like a flat radiating plate or
a convex radiating lens the operating frequency may be higher, from
80 kHz up to about 200 kHz.
* * * * *