Patent Application
20070249941
The present invention relates generally to the field of ophthalmic surgery and, more particularly, to a system and method for controlling different types of motion of a cutting tip of an ultrasonic handpiece using a class D amplifier.
The human eye functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light that can be transmitted to the retina. This deficiency is medically known as a cataract. An accepted treatment for cataracts is to surgically remove the cataract and replace the lens with an artificial intraocular lens (IOL). In the United States, most cataractous lenses are removed using a surgical technique called phacoemulsification. During this procedure, a thin cutting tip or needle is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens, which is aspirated out of the eye. The diseased lens, once removed, is replaced by an IOL.
A typical ultrasonic surgical device suitable for an ophthalmic procedure includes an ultrasonically driven handpiece, an attached cutting tip, an irrigating sleeve or other suitable irrigation device, and an electronic control console. The handpiece assembly is attached to the control console by an electric cable or connector and flexible tubings. A surgeon controls the amount of ultrasonic energy that is delivered to the cutting tip and applied to tissue by pressing a foot pedal. Tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.
The operative part of the handpiece is a centrally located, hollow resonating bar or horn that is attached to piezoelectric crystals. The crystals are controlled by the console and supply ultrasonic vibrations that drive both the horn and the attached cutting tip during phacoemulsification. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve.
A reduced pressure or vacuum source in the console draws or aspirates emulsified tissue from the eye through the open end of the cutting tip, horn bores and the aspiration line, and into a collection device. Aspiration of emulsified tissue is aided by a saline solution or other irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip.
Is One known technique is to make the incision into the anterior chamber of the eye as small as possible in order to reduce the risk of induced astigmatism. The ends of the cutting tip and the irrigating sleeve are inserted into a small incision in the cornea, sclera, or other location. These small incisions result in very tight wounds that squeeze the irrigating sleeve tightly against the vibrating tip. Friction between the irrigating sleeve and the vibrating tip generates heat. The risk of the tip overheating and burning tissue is reduced by the cooling effect of aspirated fluid flowing inside the tip. One known cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven horn, thereby emulsifying the selected tissue in situ. Other known cutting tips use piezoelectric elements that can produce a combination of longitudinal and torsional motion. However, known devices and associated longitudinal and/or torsional motion of a cutting tip can be improved.
Referring to
Known single-mode systems are not desirable for a number of reasons. First, they are not able to treat patients with different types of cutting tip motion simultaneously, which is generally referred to as “multi-mode” operation. Multi-mode treatments are desirable because, for example, torsional motion can achieve similar cutting results while generating less heat due to torsional motion being at lower frequencies than longitudinal motion. Further, known switching amplifiers are typically very inefficient and may have efficiency ratings of only 50% or lower. Known switching amplifiers can also generate substantial heat, which requires that handpieces and components thereof be designed in a particular manner to dissipate the heat, thus limiting handpiece designs. Known switching systems also consume substantial power, which is even more problematic at higher frequencies since components, such as capacitors, draw more current (and dissipate more heat) at higher frequencies. Known switching systems also include components that are relatively large in size, thus limiting designs and making the handpiece less user friendly.
Other systems provide for a combination of longitudinal and torsional movement, but they can also be improved. For example, U.S. Pat. No. 5,722,945 describes a handpiece that includes an ultrasonic vibrator and a rotational motor. The motor is coupled to the vibrator which, is coupled to an aspirating tube to impart a combined rotary and longitudinal ultrasonic reciprocating motion to the tube, which moves a tip. These known systems, however, are not desirable since they require a motor and the associated motor coupling components, separate from the ultrasonic vibrator, to generate rotational motion. For example, these types of motor driven systems may require O-ring or other seals or couplings that can fail, as well as the motors themselves. The motor components increase the complexity, size and weight of the handpiece, and make the handpiece more difficult to control.
A need, therefore, exists for systems and methods for driving cutting tips of ultrasonic handpieces in various modes and that are more efficient, generate less heat, consume less power and allow for more flexible handpiece designs. Embodiments of the invention fulfill these unmet needs.
In accordance with one embodiment of the invention, a method for controlling an ultrasonic handpiece of a phacoemulsification surgical system includes the steps of providing a first signal at a first frequency and a second signal at a second frequency as inputs to a class D amplifier and driving the ultrasonic handpiece using the output of the class D amplifier. The class D amplifier output has at least two frequency components that simultaneously move a cutting tip of the ultrasonic handpiece in different directions.
In accordance with another embodiment, a method for controlling an ultrasonic handpiece of a phacoemulsification surgical system includes the steps of providing first and second signals at respective first and second frequencies to a class D amplifier and driving the handpiece with an output of the class D amplifier so that the cutting tip of the handpiece moves with combined longitudinal and torsional motions. The first signal controls longitudinal motion of a cutting tip, and the second signal controls torsional motion of the cutting tip.
According to another alternative embodiment, a method for controlling an ultrasonic handpiece of a phacoemulsification surgical system includes the steps of providing first and second sinusoidal signals as inputs to a class D amplifier, amplifying the sinusoidal inputs; and driving the ultrasonic handpiece with the output of the class D amplifier so that the cutting tip moves with longitudinal and torsional motions at the same time. The first sinusoidal signal is at a frequency of about 40 kHz to about 45 kHz and controls longitudinal motion of a cutting tip. The second sinusoidal signal is at a frequency of about 30-34 kHz and controls torsional motion of the tip.
A further alternative embodiment is a method for controlling an ultrasonic handpiece of a phacoemulsification surgical system that includes the steps of providing first and second signals as inputs to a class D amplifier, the first and second signals being different frequencies, and driving the handpiece with an output of the class D amplifier. The class D amplifier switches between a first output at a first frequency corresponding to the first input and a second output at a second frequency corresponding to the second input to move the cutting tip in different directions at different times.
In various method embodiments, first and second signals or inputs to a class D amplifier can be combined as a third signal, which is provided as an input to the class D amplifier. Further, the first and second signals can be sinusoidal signals and can control different types of tip motion, e.g., longitudinal and torsional motions. Different types of motion can be achieved using signals at different frequencies. For example, a signal at a frequency of about 40 kHz to about 45 kHz can be used to move a cutting tip longitudinally, and a signal at a frequency of about 30-34 kHz can be used to move the cutting tip with torsional motion. Thus, the different types of motion can move the cutting tip in different planes.
Referring now to the drawings, in which like reference numbers represent corresponding parts throughout, and in which:
Embodiments of the invention drive an ultrasonic handpiece using a class D amplifier for use in both single-mode operation, in which one drive signal is provided to the handpiece at a time, and in multi-mode operation, in which the cutting tip moves with both longitudinal and torsional or rotational motion. Embodiments advantageously eliminate the need for switching amplifiers, which are commonly used in known systems. Embodiments also advantageously eliminate the need for separate motors and related components to generate rotational motion since embodiments configure and control piezoelectric element and horn components of the handpiece to generate both longitudinal and torsional motion without the need for a separate motor. Embodiments overcome the shortcomings of known systems by using a class D amplifier or other amplifier with similar capabilities, such as a class T amplifier. Class D amplifiers are commonly used in audio applications, but the inventors have discovered that incorporating class D amplifiers into ultrasonic handpieces for use in ophthalmic surgery significantly improves handpiece operation, whether switching between drive signals, or when moving the cutting tip with both longitudinal and torsional motion. Embodiments provide these capabilities together with further benefits of increasing handpiece efficiency and reducing heat generation and power consumption, which allow more flexible and user friendly handpiece designs.
Referring to
The CPU 416 may be any suitable microprocessor, micro-controller, computer or digital logic controller. The pump 418 may be a peristaltic, a diaphragm, or a Venturi pump. The power supply 420 may be any suitable ultrasonic driver, such as incorporated in the INFINITI® and LAUREATE™ surgical systems. The irrigation pressure sensor 422 may be various commercially available sensors. The valve 424 may be any suitable valve such as a solenoid-activated pinch valve. An infusion of an irrigation fluid, such as saline, may be provided by a saline source 426, which may be any commercially available irrigation solution provided in bottles or bags.
In use, the irrigation pressure sensor 422 is connected to the handpiece 412 and the infusion fluid source 426 through irrigation lines 430, 432 and 434. The irrigation pressure sensor 422 measures the flow or pressure of irrigation fluid from the source 426 to the handpiece 412 and supplies this information to the CPU 416 through the cable 436. The irrigation fluid flow data may be used by the CPU 416 to control the operating parameters of the console 414 using software commands. For example, the CPU 416 may, through a cable 440, vary the output of the power supply 420 being sent to the handpiece 412 and the tip 413 though a power cable 442. The CPU 416 may also use data supplied by the irrigation pressure sensor 422 to vary the operation of the pump 418 and/or valves through a cable 444. The pump 418 aspirates fluid from the handpiece 412 through a line 446 and into a collection container 428 through line 448. The CPU 416 may also use data supplied by the irrigation pressure sensor 422 and the applied output of power supply 420 to provide audible tones to the user. Additional aspects of exemplary surgical systems can be found in U.S. Pat. No. 6,261,283 (Morgan, et al.), the contents of which are incorporated herein by reference.
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The location of longitudinal and torsional nodal points (the points with zero velocity of the respective mode) is important for proper functioning of the handpiece 500. The torsional node 530 preferably is located at the proximal longitudinal node 532, so that the torsional node 530 and the longitudinal node 532 are coincident, e.g., both of which are located on the plug 520. The handpiece 500 also has a distal longitudinal node 534 located at reduced diameter portion 536 of the horn 510. Further aspects of a suitable handpiece 500 are provided in Patent Application Publication No. US 2006/0041220 A1, the contents of which are incorporated herein by reference.
Referring to
Persons skilled in the art will appreciate that these method steps can be performed in various orders. For example, steps 610 and 620 may occur sequentially, in a different order or simultaneously. Further, persons skilled in the art will appreciate that a class D amplifier can be used to switch between two signals or, alternatively to switch among three or more signals depending on the class D amplifier capabilities.
Two signal sources 710 (Signal Source 1) and 720 (Signal Source 2) (generally 710) are shown in
Embodiments using a class D amplifier for single-mode operation provide a number of improvements over known systems that use switching amplifiers. For example, the system 700 operates with improved efficiency, which can be about 90% rather than about 50%. The system 700 also generates less heat relative to known systems, thus providing more flexibility in terms of component and system design, size, weight and heat dissipation. The system 700 also consumes less power than known systems, and these power advantages are particularly notable at higher frequencies.
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In the embodiment illustrated in
In the embodiment shown in
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According to one embodiment, in step 1310, a first input signal is received as an input to a class D amplifier. The first signal has a frequency between about 30 kHz and 34 kHz and is used for torsional motion. In step 1320, a second signal is received, and the second signal can have a frequency of about 40 KHz and 45 KHz. The second signal is used for longitudinal motion. In step 1330, the first and second signals can be combined (if necessary), and in step 1340, the combined signal is provided to the class D amplifier. In step 1350, the class D amplifier amplifies the combined signal, and in step 1350, the output of the class D amplifier drives the cutting tip of the handpiece 500 so that the handpiece tip moves with combined longitudinal and torsional motion at the same time. As discussed above with respect to
Referring to
Thus, different types of motion of the cutting tip of the handpiece can define different planes of motion. A first type of motion can define a first plane, and a second, different type of motion can define a second plane. The two planes can be substantially perpendicular to each other when the first motion is longitudinal motion and the second motion is torsional motion. Other types of crystal designs, horn configurations and harmonics may result in planes of motion that are defined or arranged in other angular arrangements that may or may not be perpendicular.
Persons skilled in the art will recognize that different frequencies may be used depending upon the construction of piezoelectric crystals and the handpiece. Thus, the exemplary frequencies and frequency ranges for torsional and longitudinal motion are provided for purposes of explanation, not limitation. Further, various crystal and handpiece configurations can be used with the same or different frequencies to provide simultaneous longitudinal and torsional motion when driven by a class D amplifier.
Class D amplifiers suitable for embodiments of the invention are well known and used in audio applications. Various known class D amplifiers can be incorporated into ophthalmic surgical systems to drive ultrasonic handpieces according to embodiments of the invention, including class D amplifier described in “Class D Amplifier for a Power Piezoelectric Load,” by K. Agbossou et al. and Application Note AN-1071, “Class D Amplifier Basics,” by J. Honda et al., International Rectifier, 233 Kansas Street, El Segundo, Calif., the contents of which are incorporated herein by reference. For reference, FIGS. 16A-C illustrate the components and operation of a typical class D amplifier. As illustrated, class D amplifiers generally operate by providing an input signal and a high frequency triangular wave to an error amplifier. The error amplifier generates a pulse width modulated (PWM) signal, which is provided to a controller. The controller drives Output/Power (O/P) switches, which are either on or off, thereby reducing power losses and increasing efficiency. A low pass filter reconstructs the original signal and removes a high frequency PWM carrier frequency.
Persons skilled in the art will appreciate that other amplifiers, such as class T amplifiers, can be used with embodiments of the invention. Embodiments advantageously use a class D amplifier or other suitable amplifier for driving a cutting tip to move with different types of motion at the same time rather than driving a cutting tip at one frequency at a time, while improving the operating parameters of the system. Embodiments provide a system that is more efficient, generates less heat, and dissipates substantially constant power over different frequencies. Further, embodiments provide a system that has smaller dimensions and less weight. Moreover, since less heat is generated, air-flow and power system requirements are relaxed. Thus, embodiments of the invention provide significant improvements over known ultrasonic handpieces and control systems that are less efficient, switch between different frequencies, generate more heat and use larger and additional components, such as switching amplifiers and separate motors for generating rotational motion.
Although references have been made in the foregoing description to various embodiments, persons of skilled in the art will recognize that insubstantial modifications, alterations, and substitutions can be made to the described embodiments without departing from the scope of embodiments.
