Surgery – Instruments – Cutting – puncturing or piercing
Reexamination Certificate
2000-12-19
2002-12-10
Nerbun, Peter (Department: 3731)
Surgery
Instruments
Cutting, puncturing or piercing
C310S334000
Reexamination Certificate
active
06491708
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to ultrasonic transducer assemblies and, in particular to transducer assemblies of the composite or sandwich type with a compression assembly for providing a more uniformly compressive loading to the transducer assembly.
Ultrasonic transmission devices are well known for use in a variety of applications, such as surgical operations and procedures. The ultrasonic transmission devices usually include a transducer that converts electrical energy into vibrational motion at ultrasonic frequencies. The vibrational motion is transmitted to vibrate a distal end of a surgical instrument. Such uses are disclosed in representative U.S. Pat. Nos. 3,636,943 and 5,746,756, both incorporated herein by reference.
High-intensity ultrasonic transducers of the composite or sandwich type typically include front and rear mass members with alternating annular piezoelectric transducers and electrodes stacked therebetween. Most such high-intensity transducer are of the pre-stressed type. They employ a compression bolt that that extends axially through the stack to place a static bias of about one-half of the compressive force that the piezoelectric (PZT) transducers can tolerate. Sandwich transducers utilizing a bolted stack transducer tuned to a resonant frequency and designed to a half wavelength of the resonant frequency are described in United Kingdom Patent No. 868,784. When the transducers operate they are designed to always remain in compression, swinging from a minimum compression of nominally zero to a maximum peak of no greater than the maximum compression strength of the material.
As shown in
FIG. 1
, an acoustic or transmission assembly
80
of an ultrasonic device generally includes a transducer stack or assembly
82
and a transmission component or working member. The transmission component may include a mounting device
84
, a transmission rod or waveguide
86
, and an end effector or applicator
88
. The transmission rod
86
and end effector
88
are preferably part of a surgical instrument.
The transducer assembly
82
of the acoustic assembly
80
converts the electrical signal from a generator (not shown) into mechanical energy that results in longitudinal vibratory motion of the end effector
88
at ultrasonic frequencies. When the acoustic assembly
80
is energized, a vibratory motion standing wave is generated through the acoustic assembly
80
. The amplitude of the vibratory motion at any point along the acoustic assembly
80
depends on the location along the acoustic assembly
80
at which the vibratory motion is measured. The transducer assembly
82
, which is known as a “Langevin stack”, generally includes a transduction portion
90
, a first resonator or aft end bell
92
, and a second resonator or fore end bell
94
. The transducer assembly
82
is preferably an integral number of one-half system wavelengths (n&lgr;/2) in length.
The distal end of the first resonator
92
is connected to the proximal end of transduction section
90
, and the proximal end of the second resonator
94
is connected to the distal end of transduction portion
90
. The first and second resonators
92
and
94
are preferably fabricated from titanium, aluminum, steel, or any other suitable material. The first and second resonators
92
and
94
have a length determined by a number of variables, including the thickness of the transduction section
90
, the density and modulus of elasticity of material used in the resonators
92
and
94
, and the fundamental frequency of the transducer assembly
82
. The second resonator
94
may be tapered inwardly from its proximal end to its distal end to amplify the ultrasonic vibration amplitude.
The transduction portion
90
of the transducer assembly
82
preferably comprises a piezoelectric section (“PZTs”) of alternating positive electrodes
96
and negative electrodes
98
, with piezoelectric elements
100
alternating between the electrodes
96
and
98
. The piezoelectric elements
100
may be fabricated from any suitable material, such as, for example, lead zirconate-titanate, lead meta-niobate, lead titanate, or ceramic piezoelectric crystal material. Each of the positive electrodes
96
, negative electrodes
98
, and piezoelectric elements
100
have a bore extending through the center. The positive and negative electrodes
96
and
98
are electrically coupled to wires
102
and
104
, respectfully. The wires
102
and
104
transmit the electrical signal from the generator to electrodes
96
and
98
.
The piezoelectric elements
100
are energized in response to the electrical signal supplied from the generator to produce an acoustic standing wave in the acoustic assembly
80
. The electrical signal causes disturbances in the piezoelectric elements
100
in the form of repeated small displacements resulting in large compression forces within the material. The repeated small displacements cause the piezoelectric elements
100
to expand and contract in a continuous manner along the axis of the voltage gradient, producing high frequency longitudinal waves of ultrasonic energy. The ultrasonic energy is transmitted through the acoustic assembly
80
to the end effector
88
.
The piezoelectric elements
100
are conventionally held in compression between the first and second resonators
92
and
94
by a bolt and washer combination
106
. The bolt
106
preferably has a head, a shank, and a threaded distal end. The bolt
106
is inserted from the proximal end of the first resonator
92
through the bores of the first resonator
92
, the electrodes
96
and
98
, and piezoelectric elements
100
. The threaded distal end of the bolt
106
is screwed into a threaded bore in the proximal end of second resonator
94
.
Other embodiments of the prior art utilize a stud that is threadedly engaged with both the first and second resonators
92
and
94
to provide compressive forces to the PZT stack. Threaded studs are also known in the prior art for attaching and detaching transmission components to the transducer assembly. See, for example, U.S. Pat. Nos. 5,324,299 and 5,746,756. Such bolts and studs are utilized to maintain acoustic coupling between elements of the sandwich type transducer or any attached acoustic assembly. Coupling is important to maintain tuning of the assembly, allowing the assembly to be driven in resonance.
The problem with the prior art is that the compression means is inadequate and is unable to provide a uniform pressure across the inside diameter to the outside diameter of each PZT and through the entire PZT stack, the “r” and “z” axes as shown in FIG.
1
and graphically illustrated in
FIG. 2. A
Finite Element analysis shows that the ratio of the pressure in the r axis is of the order of 4:1.
Non-uniform pressure across the r and z axes reduces transducer efficiency and leads to high heat generation. This limitation becomes acutely critical in temperature-limited applications. In temperature-limited applications, the reduced efficiency translates into higher heat generation in the transducer and reduced maximum output. Further, non-uniform pressure limits the magnitude of compression and therefore limits the power capability of the transducer.
U.S. Pat. No. 5,798,599 discloses an ultrasonic transducer assembly which includes soft, aluminum foil washers disposed between facing surfaces of adjacent members of the PZT stack. The washers deform under compressive loading to follow the surface irregularities of the adjacent member surfaces.
There is a need therefore, for an ultrasonic transducer that exhibits substantially uniform compressive stresses across each PZT and throughout the PZT stack to reduce heat generation and increase power output efficiency. This invention meets this need.
SUMMARY OF THE INVENTION
The invention is an ultrasonic device with increased efficiency as a result of substantially increased pressure uniformity across individual PZTs and through the PZT stack. The invention comprises a transducer assembly adapted to vibrate at an ultrasonic
Beaupre Jean M.
Madan Ashvani K.
Ethicon Endo-Surgery Inc.
Kreger Verne E.
Moran Katherine
Nerbun Peter
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