Ultrasonic handpiece assembly

Abstract

The ultrasonic handpiece assembly comprises a horn, a rear mass attached to the rear end of the horn, a needle attached to the front end of the horn, a stack of piezoelectric elements coaxially arranged around the horn, and an LT spring coaxially arranged around the horn behind the stack. The horn includes a low-gain section in front of the stack and a high-gain section in front of the low-gain section. The assembly has a first LT mode, a T mode, a second LT mode, and an L mode at different resonant frequencies. The low-gain horn section includes circumferential grooves located at the vibration nodes of the LT modes. Frequency separation between the first LT mode and the T mode allows the torsional vibration of the first LT mode to constructively interact with the torsional vibration of the T mode, thereby increasing the torsional stroke in the T mode.

Description

[Technical Field]

[0001]

[0001] (Cross-reference of related applications) This application claims priority to U.S. Patent Application No. 18 / 195,450, filed on 10 May 2023, the entire disclosure of which is incorporated herein by reference.

[0002]

[0002] (Field of Invention) The present invention generally relates to an ultrasonic handpiece used, for example, in cataract surgery to emulsify cataract tissue and aspirate it from the eye. [Background technology]

[0003]

[0003] Historically, cataract surgery has been performed using ultrasonic handpieces that provide a longitudinal or "jackhammer" motion at the tip of the needle that the handpiece receives. A high-power longitudinal-mode ultrasonic handpiece used in cataract surgery typically consists of the components depicted in Figure 1. The surgical needle is screwed into a stepped horn ultrasonically driven by a stack of piezoelectric ceramic elements. A spacer is positioned behind the stack of ceramic elements. A rear mass with a mount, isolation tube, and Luer connector is screwed onto a central bolt that passes through the stack. When rotational force is applied, the rear mass compresses and preloads the stack. A lumen for aspirating fragmented cataract tissue enters the horn through the needle, enters the rear mass through the central bolt, exits the Luer connector, and enters a flexible tube attached to a pump. One O-ring bore seal is positioned behind the stepped section of the horn, and the other is positioned on the rear mount, thereby providing a waterproof barrier inside the handpiece housing.

[0004]

[0004] In a handpiece in longitudinal mode ("L mode"), excision occurs only during half of the oscillation cycle when the needle tip is advancing toward the cataract. During the other half of the cycle when the needle tip is moving away from the cataract, the needle tip does not excise, but energy is required throughout the entire cycle and heat is generated. As a result, the excision efficiency is not optimized and the excision time increases. The axial distance between the longitudinally retracted and extended positions of the needle tip during longitudinal oscillation is referred to as the "longitudinal stroke".

[0005]

[0005] Torsional-mode ultrasonic cataract aspiration was introduced by Alcon in 2006 in the form of the OZil® handpiece, the internal assembly of which is shown in Figure 2. The OZil® handpiece transmits both longitudinal and torsional motion to the needle, and depending on the shape of the tip, excision is performed by either rotational shear motion or transverse shear motion. Some of the longitudinal vibrations generated by the stack are converted into torsional motion by a torsion spring integrally formed by machining on the horn of the OZil® handpiece shown in Figure 2. A curved tip needle with a Kelman structure amplifies the torsion of the shaft by lateral rotational motion at the tip, while a needle with a straight or flared tip performs excision by rotational motion amplified by the distance between the center of the needle and the outermost excision end of the tip. When the needle tip moves laterally or rotates in torsional mode ("T-mode"), more of the margin is used to excise rather than repel the cataract tissue, and the needle tip maintains contact with the cataract tissue throughout the entire cycle, resulting in more efficient excision than with a handpiece in longitudinal mode only. The angular distance the needle tip moves from one side to the other during torsional vibration is called the "torsional stroke."

[0006]

[0006] Improvements in the OZil® handpiece assembly are described in U.S. Patent No. 8,395,299 (Bromfield), the full disclosure of which is incorporated herein by reference. Unlike the OZil® handpiece, in which the spring that converts part of the longitudinal motion into torsional motion is integrated into the horn, the Bromfield design incorporates the spring as a separate component into the handpiece. This significantly increases the design freedom, facilitating alternative configurations and alternative spring materials to achieve different performance objectives. Figure 3 shows a prior art longitudinal-torsional (LT) mode ultrasonic handpiece assembly developed by applicant Moog Inc. based on the Bromfield design. Similar to the OZil® handpiece assembly, the Moog LT handpiece assembly provides ophthalmologists with the ability to switch between a nearly torsional motion mode and a nearly longitudinal motion mode during cataract surgery. [Overview of the project]

[0007]

[0007] An object of this disclosure is to increase the torsional stroke of an ultrasonic LT handpiece for a given electric drive power, thereby improving the performance of the LT handpiece when operated by a surgeon in T mode.

[0008]

[0008] Another object of this disclosure is to make the LT handpiece lighter and smaller, thereby improving ease of use during surgery, while achieving the aforementioned performance improvements.

[0009]

[0009] To facilitate these and other purposes, ultrasonic LT handpiece assemblies are disclosed. The handpiece assembly generally comprises a horn, a rear mass, a needle, a plurality of piezoelectric elements, and an LT spring. The horn is elongated along a longitudinal axis and includes a rear end, a front end opposite the rear end, and a horn lumen extending axially through the horn. A rear mass, which may be screw-mounted to the rear end of the horn, has a rear mass lumen extending axially through the rear mass and communicating with the horn lumen. A needle, which may be screw-mounted to the front end of the horn, has a needle lumen, which extends axially through the needle and communicates with the horn lumen. The plurality of piezoelectric elements are arranged coaxially around the horn in a stack, and the LT spring may be arranged coaxially around the horn adjacent to the stack of piezoelectric elements and axially rear of the stack.

[0010]

[0010] The horn includes a low-gain section located axially forward of the stack of piezoelectric elements and a high-gain section located axially forward of the low-gain section, wherein the high-gain section has a smaller cross-sectional area than the low-gain section.

[0011]

[0011] The ultrasonic handpiece assembly has a first LT mode at a first resonant frequency, a T mode at a second resonant frequency, a second LT mode at a third resonant frequency, and an L mode at a fourth resonant frequency. According to the present disclosure, the low-gain section of the horn includes a circumferential groove positioned in the axial location corresponding to the vibration node of the first resonant LT mode of the handpiece assembly. The frequency separation between the lower resonant frequency of the first LT mode and the higher resonant frequency of the T mode allows the torsional vibration of the first LT mode to constructively interact with the torsional vibration of the T mode, thereby increasing the torsional stroke of the ultrasonic handpiece assembly in the T mode.

[0012]

[0012] The properties and modes of operation of the present disclosure will now be described in more detail by embodiments for carrying out the invention, with reference to the accompanying drawings.

Brief Description of the Drawings

[0013] [Figure 1]

[0013] Perspective view of a longitudinal (L) mode ultrasonic handpiece assembly according to the prior art. [Figure 2]

[0014] Perspective view of a longitudinal-torsional (L-T) mode ultrasonic handpiece assembly according to the prior art. [Figure 3]

[0015] Perspective view of another L-T mode ultrasonic handpiece assembly according to the prior art. [Figure 4]

[0016] Perspective view of an L-T mode ultrasonic handpiece assembly according to an embodiment of the present disclosure. [Figure 5]

[0017] Longitudinal cross-sectional perspective view of the L-T mode ultrasonic handpiece assembly shown in FIG. 4. [Figure 6]

[0018] Graph illustrating the low-power impedance sweep of the handpiece assembly of FIG. 4. [Figure 7]

[0019] Plot of the resonance frequency as a function of the horn length in the first L-T mode and T mode of the prior art handpiece assembly shown in FIG. 3. [Figure 8]

[0020] Plot of the effective coupling (Keff) as a function of the horn length in the first L-T mode and T mode of the prior art handpiece assembly shown in FIG. 3. [Figure 9]

[0021] Plot of the torsional stroke as a function of the horn length in the T mode of the prior art handpiece assembly shown in FIG. 3. [Figure 10]

[0022] Plot of the resonance frequency as a function of the groove depth in the first L-T mode, T mode, second L-T mode, and L mode of the grooved L-T handpiece assembly according to the present disclosure. [Figure 11]

[0023] This is a plot of the effective coupling (Keff) as a function of groove depth in the first LT mode, T mode, second LT mode, and L mode for the grooved LT handpiece assembly according to the present disclosure. [Figure 12]

[0024] Elevation views showing the prior art Alcon OZil® handpiece assembly, the prior art Moog LT handpiece assembly, and the grooved LT handpiece assembly according to the present disclosure, as tested by the applicant, with the handpiece assembly shown without the needle. [Figure 13]

[0025] Figure 2 shows the Alcon OZil® handpiece assembly, Figure 3 shows the Moog LT handpiece assembly, and Figure 3 shows the grooved LT handpiece assembly of this disclosure. The plots show the torsional stroke as a function of drive voltage, illustrating the measurement results of high-power tests performed on these handpiece assemblies. [Figure 14]

[0026] Figure 2 shows the Alcon OZil® handpiece assembly, Figure 3 shows the Moog LT handpiece assembly, and Figure 3 shows the grooved LT handpiece assembly of this disclosure. The plots show the torsional stroke as a function of apparent drive power, illustrating the measurement results of high-power tests performed on these handpiece assemblies. [Figure 15]

[0027] Figure 3 is an elevation view showing the grooved handpiece assembly of the present disclosure alongside the Moog LT handpiece assembly, with the handpiece assembly shown without the needle. [Modes for carrying out the invention]

[0014]

[0028] Figures 4 and 5 show an LT ultrasonic handpiece assembly 10 formed according to an embodiment of the present invention. The handpiece assembly 10 may generally include a horn 12, a rear mass 14, a needle 16, a plurality of piezoelectric elements 18A to 18F, an LT spring 20, and a spacer 22.

[0015]

[0029] The horn 12 is elongated along the longitudinal axis 11 and includes a rear end 24, a front end 26 opposite the rear end, and a horn lumen 28 extending axially through the horn. The rear mass 14 may be attached to the rear end 24, for example, by fitting mounting threads and / or by a friction engagement seal 30, and has a rear mass lumen 32 that extends axially through the rear mass and communicates with the horn lumen 28. The needle 16 may be attached to the front end 26 of the horn 12 by screwing, and has a needle lumen 17 that extends axially through the needle and communicates with the horn lumen 28. Multiple piezoelectric elements 18A to 18F are arranged coaxially around the horn 12 in a stack 18. The piezoelectric elements 18A to 18F are electrically connected in parallel and convert an AC drive voltage into longitudinal oscillation motion at the frequency of the AC drive voltage. The piezoelectric elements 18A-18F may be piezoelectric ceramic rings, such as PZT8 ceramic rings. The LT spring 20 may be coaxially positioned around the horn 12 adjacent to the stack 18 of piezoelectric elements 18A-18D and axially rearward from the stack 18, and is configured to convert the vibrational longitudinal driving motion generated by the piezoelectric stack 18 into both longitudinal and torsional motion at the tip 34 of the needle 16. For example, the LT spring 20 may include a plurality of helical grooves 36 formed on the outer cylindrical surface of the LT spring body. The grooves 36 may be generated in the same way as linear grooves by rotating the needle LT spring 20 during groove formation. Additional and / or alternative embodiments and details of the LT spring 20 are described in Bromfield's U.S. Patent No. 8,395,299, mentioned above. The horn 12 mechanically amplifies both the torsional and longitudinal resonant vibrational motions generated by the piezoelectric stack 18 and the LT spring 20. The motion generated at the tip 34 of the needle is used, for example, to emulsify the cataract portion during surgery for removal. The length of the assembly 10 can be adjusted using the axially rear spacer 22 of the LT spring 20, thereby changing the resonant frequencies of the torsional and longitudinal vibration modes.

[0016]

[0030] The horn 12 includes a low-gain section 40 axially forward of the stack 18 of piezoelectric elements 18A to 18D, and a high-gain section 42 axially forward of the low-gain section 40. The high-gain section 42 has a smaller cross-sectional area (i.e., the cross-sectional area viewed in the direction of the longitudinal axis 11) than the low-gain section 40. The low-gain section 40 and the high-gain section 42 may be cylindrical in shape, and a radial step 41 may provide a transition between the low-gain section 40 and the high-gain section 42. The low-gain section 40 may have a circumferential groove configured to hold a compliant O-ring fluid seal 43 in close proximity to the axial position of the radial step 41.

[0017]

[0031] The horn 12 may have a central bolt 44 that extends rearward from the low-gain section 40 and passes through aligned openings of the piezoelectric elements 18A-18F, the LT spring 20, and the spacer 22. The central bolt 44 may be screwed into the rear mass 14, thereby generating a compressive prestress that holds the piezoelectric stack 18 together when a torsional load is applied to the rear mass. Compressive prestress is necessary in high-power handpiece assemblies to prevent dynamic tensile stress from exceeding the tensile strength of the ceramic piezoelectric elements 18A-18F and causing them to break.

[0018]

[0032] Assembly 10 may further include an isolation tube 45, a heel mass 46, and a tapered Luer connector 47 integrated with the rear mass 14. The heel mass 46 may have a circumferential groove for receiving a radial spring or a compliant O-ring fluid seal 48. The Luer connector 47 allows a flexible medical-grade tube (not shown) to be attached to assembly 10 to fluidize into a suction lumen collectively defined by the needle lumen 17, the horn lumen 28, and the rear mass lumen 32. The suction lumen allows suction of fragmented cataract portions through assembly 10, exiting the Luer connector 47 and entering the attached medical-grade tube. The heel mass 46, combined with the Luer connector 47, vibrates together with the isolation tube 45 at a resonant frequency much lower than the torsional and longitudinal resonant frequencies. As a result, the rear mass 14 can function as a rear mount from which the assembly 10 can be mounted to an external housing (not shown), acting as a spring-mass vibration isolation system in which the vibration nodes of the assembly 10 in T-mode and L-mode substantially coincide at the heel mass 46 and radial spring / O-ring 48. In addition to the vibration nodes mentioned for the rear mount position, there are vibration nodes in T-mode and L-mode substantially coincide at the O-ring 43, which can function as a front mount from which the assembly 10 can be mounted to an external housing. The rear and front mount positions corresponding to the vibration nodes provide positions in which the handpiece assembly can be mounted to an external housing to eliminate or significantly reduce the dissipation of vibration energy resulting from damping. The central vibration node may be located inside the stack of piezoelectric ceramic elements with the highest local strain to maximize the vibration amplitude.

[0019]

[0033] The horn 12, rear mass 14, needle 16, LT spring 20, and spacer 22 may be manufactured as metallic components from, for example, titanium alloy Ti-6A1-4V, which provides biocompatibility, good spring and fatigue properties, and a high stiffness-to-density ratio. Alternative materials for the horn 12, rear mass 14, LT spring 20, and spacer 22 include aluminum alloy, stainless steel, and beryllium copper. Naturally, other suitable materials may be used without departing from the present invention.

[0020]

[0034] In one embodiment, the low-gain section 40 of the horn 12 has a diameter of 1 / 2 inch and a length of 1.16 inches. The high-gain section 42 of the horn 12 has a diameter of 0.15 inches and a length of 1.13 inches. The piezoelectric elements 18A to 18F are ring-shaped ceramic elements with an outer diameter of 1 / 2 inch, an inner diameter of 0.197 inches, and an axial thickness (i.e., length) of 0.08 inches, and the spacer 22 has a diameter of 1 / 2 inch and a length of 0.11 inches.

[0021]

[0035] In another embodiment, the low-gain section 40 of the horn 12 has a diameter of 3 / 8 inch and a length of 1.16 inches. The high-gain section 42 of the horn 12 has a diameter of 0.14 inches and a length of 0.915 inches. The piezoelectric elements 18A-18F are ring-shaped ceramic elements with an outer diameter of 3 / 8 inch, an inner diameter of 0.193 inches, and an axial thickness (i.e., length) of 0.08 inches, while the spacer 22 has a diameter of 3 / 8 inch and a length of 0.21 inches.

[0022]

[0036] As can be seen in Figures 4 and 5, the low-gain section 40 of the horn 12 includes a circumferential groove 50. According to this disclosure, including the details described below, the groove 50 is positioned and configured to increase the torsional stroke of the handpiece assembly 10 in T mode.

[0023]

[0037] Next, we consider Figure 6, which shows the impedance as a function of frequency measured during a low-power impedance sweep of the handpiece assembly 10. As can be seen, the handpiece assembly 10 has a first LT mode at a first resonant frequency F1, a T mode at a second resonant frequency F2, a second LT mode at a third resonant frequency F3, and an L mode at a fourth resonant frequency F4. In the graph of Figure 6, the first resonant frequency F1 corresponding to the first LT mode is approximately 26.9 kHz, the second resonant frequency F2 corresponding to the T mode is approximately 28.3 kHz, the third resonant frequency F3 corresponding to the second LT mode is approximately 33.8 kHz, and the fourth resonant frequency F4 corresponding to the L mode is approximately 41.0 kHz. The vibrational motion in the first and second LT modes is distributed throughout the entire length of the handpiece assembly. The operating modes in cataract surgery are the T mode and the L mode. The nearly torsional vibration mode (T-mode) is driven at a second resonant frequency F2, and the nearly longitudinal vibration mode (L-mode) is driven at a fourth resonant frequency F4, which is different from the second resonant frequency F2.

[0024]

[0038] For the reasons described below, the circumferential groove 50 is positioned in an axial location corresponding to the vibration node of the first LT mode of the handpiece assembly 10, and may be configured such that the torsional vibration of the first LT mode of the handpiece assembly 10 constructively interacts with the torsional vibration of the handpiece assembly 10 in the T mode to increase the torsional stroke of the handpiece assembly in the T mode.

[0025]

[0039] The inventors determined that when the T-mode frequency F2 exceeds the first LT-mode frequency F1 by approximately 1.3 to 2.2 kHz, a constructive interaction occurs between the T-mode vibration and the first LT-mode vibration, thereby increasing the torsional stroke of the T-mode. Furthermore, the inventors determined that when the T-mode frequency F2 is lower than the first LT-mode frequency F1, the interaction between the T-mode vibration and the first LT-mode vibration is destructive, and the torsional stroke of the T-mode decreases.

[0026]

[0040] The resonant frequencies F1 of the first LT mode and F2 of the T mode are partially dependent on the horn shape. For example, Figure 7 demonstrates that as the axial length of the horn increases, the T mode frequency F2 decreases from approximately 30.5 kHz to approximately 27 kHz. Figure 7 also demonstrates that for the same increase in horn length, the change in the resonant frequency F1 of the first LT mode is remarkably small. The T mode resonant frequency F2 starts at a frequency approximately 2.2 kHz above the first LT mode resonant frequency F1. At a horn length of approximately 27.1 mm, the T mode resonant frequency F2 intersects with the first LT mode resonant frequency F1, and as the horn length increases further, it falls below the first LT mode resonant frequency F1 and diverges from the first LT mode resonant frequency F1.

[0027]

[0041] Figure 8 shows that increasing the horn length improves the effective coupling of the T mode and the first LT mode (K eff This illustrates the effect on (). Effective binding K eff It is calculated as follows:

[0028]

number

[0029] Here, f R and f AR These are, for example, the resonant and anti-resonant frequencies of the active resonant mode plotted in Figure 6. Effective coupling K eff This represents the ability of a handpiece assembly with a piezoelectric transducer element to convert electrical energy into mechanical energy, and the ability to convert mechanical energy into electrical energy. In the case of an LT handpiece, power in the form of a drive voltage is converted into mechanical force in the form of oscillating motion. In summary, Figures 7 and 8 show that for T-mode frequencies F2 higher than the first LT-mode frequency F1, the interaction between these modes increases as the frequency difference between the T-mode and the first LT-mode decreases, increasing the effective coupling of the T-mode, which reaches a maximum when the two modes merge.

[0030]

[0042] Next, refer to Figure 9 along with Figure 7. The maximum effective coupling is achieved by converting a low drive voltage into high oscillating motion, and Figures 7 and 9 show that the best performance corresponding to the peak torsional stroke occurs for a T-mode resonant frequency F2 approximately 1.6 kHz higher than the first LT-mode resonant frequency F1. Figures 7 and 9 also demonstrate that when the T-mode resonant frequency F2 is 1.3 kHz to 2.2 kHz higher than the first LT-mode resonant frequency F1, the torsional stroke is high, exceeding 140 μm. However, at a horn length of approximately 27.1 mm, the T-mode resonant frequency F2 falls below the first LT-mode resonant frequency F1, and the torsional stroke decreases significantly, continuing to decrease as the horn length increases and the T-mode resonant frequency decreases. This indicates that when the T-mode resonant frequency F2 exceeds the first LT-mode resonant frequency F1 by approximately 1.3 kHz to 2.2 kHz, a constructive interaction occurs between the T-mode and the first LT-mode, increasing the torsional stroke. Furthermore, if the T-mode resonance frequency F2 is lower than the first LT-mode resonance frequency F1, the interaction between the T-mode and the first LT-mode is destructive and reduces the torsional stroke.

[0031]

[0043] The grooved handpieces depicted in Figures 4 and 5 utilize this unique interaction between the T-mode and the first LT-mode by positioning the circumferential groove 50 of the horn 12 in an axial position corresponding to the vibration node of the first LT-mode, and by adjusting the first LT-mode resonance frequency F1 with respect to the T-mode resonance frequency F2 by changing the groove depth instead of changing the horn length.

[0032]

[0044] The effect of the groove 50 of the horn 12 on the performance of the handpiece assembly 10 was analyzed using a finite element model in which the cylindrical low-gain section 40 of the horn 12 is specified in 1 / 2-inch diameter and other dimensions of the 1 / 2-inch diameter embodiment described above. As mentioned, the groove 50 is intentionally positioned to coincide with the vibration node of the first LT mode, which has the smallest vibration amplitude. The width of the groove 50 along the axis 11 was specified to 0.22 inches. The depth of the groove can be varied to tune the resonant frequency F1 of the first LT mode to the resonant frequency F2 of the T mode, as illustrated in Figure 10. The resonant frequencies F1 of the first LT mode and F3 of the second LT mode decrease significantly as the groove depth increases, while the resonant frequencies F2 and F4 of the T mode and L mode, respectively, change very little as the groove depth increases. Thus, by varying the depth of the groove 50, it is possible to tune the first LT mode resonant frequency F1 to the T mode resonant frequency F2.

[0033]

[0045] Next, refer to Figure 11 along with Figure 10. In the absence of a groove (i.e., groove depth = 0), the T-mode resonance frequency F2 is approximately 2000 Hz lower than the first LT-mode resonance frequency F1, and the effective coupling coefficient K is low at 0.05. eff This is achieved. With a groove depth of 0.07 inches (1.8 mm), the frequency difference between the T-mode resonant frequency F2 and the first LT-mode resonant frequency F1 is approximately 1.4 kHz, and this frequency difference is within the preferred range of 1.3 kHz to 2.2 kHz, with the first LT-mode frequency being lower than the T-mode frequency. Effective coupling in T-mode K eff This increases significantly from 0.05 in the case of no groove to approximately 0.16 in the case of a groove depth of 0.07 inches. Further increasing the groove depth to 0.078 inches increases the separation between the T-mode resonant frequency F2 and the first LT-mode resonant frequency F1, resulting in effective coupling K eff It decreases to 0.10. In the resonant frequency separation when the T-mode frequency F2 is higher than the first LT-mode frequency F1, the torsional vibration of the first LT-mode constructively interacts with the torsional vibration of the T-mode.

[0034]

[0046] Based on the analysis of the finite element model described above, a prototype embodiment of an ultrasonic handpiece assembly 10 (a "grooved L-T" assembly) having a low-gain horn section with a 0.07-inch deep groove and a 1 / 2-inch diameter was tested against the Alcon OZil® handpiece assembly shown in FIG. 2 and the Moog L-T handpiece assembly shown in FIG. 3. The tested Alcon OZil® and Moog L-T handpiece assemblies also comprise a horn having a 1 / 2-inch diameter low-gain section. The Alcon OZil® and Moog L-T assemblies each have four PZT8 ceramic rings, while the Grooved L-T assembly has six PZT8 ceramic rings. Low-power and high-power tests were performed on the OZil® handpiece assembly with an Alcon 21-gauge bent tip needle attached, and the 1 / 2-inch Moog L-T and 1 / 2-inch grooved L-T handpiece assemblies each having a 19-gauge straight needle with a 30° beveled cutting tip. These needles are frequently selected by surgeons for use with these handpieces. The tested handpiece assemblies are shown side by side in FIG. 12 without the needles attached.

[0035]

[0047] Low-power test:

[0048] The test began with a low-power impedance sweep versus frequency to measure and compare the main performance characteristics of the piezoelectric transducer handpiece assembly. The characteristics of the transducer resonance modes obtained from the sweep include the resonance frequency (f min ) at the minimum impedance (Z R ), the anti-resonance frequency (f max ) at the maximum impedance (Z AR ), and the effective coupling coefficient (K eff) is calculated using the above formula. Using data from low-power impedance sweep, the mechanical quality factor Q represents the vibration stroke amplitude boost resulting from resonance. M We also calculated the following. Typically, when the drive voltage is limited, a larger quality factor increases the vibration amplitude. Mechanical quality factor Q M and the effective coupling coefficient K eff The product of the square of the impedance is a useful figure of merit (FOM) that characterizes the resonance intensity and the piezoelectric transducer's ability to convert power into mechanical force. Furthermore, low-frequency capacitance is also measured during low-power impedance sweep.

[0036]

[0049] The results from these sweeps on each handpiece assembly are shown in Table 1.

[0037] [Table 1]

[0038]

[0050] The first LT mode of the OZil® handpiece assembly has a resonant frequency 5345 Hz lower than the T mode resonant frequency, which is considerably above the preferred range of 1.3 kHz to 2.2 kHz for constructive interaction between these modes that increases torsional stroke. In the case of Moog's LT handpiece assembly, the separation of the resonant frequencies between the T mode and the first LT mode is 2330 Hz, which is slightly outside the preferred range for constructive interaction. In the case of grooved LT handpiece assembly, the arrangement and depth of the grooves result in a resonant frequency separation from the T mode to the first LT mode of 1417 Hz, which is within the preferred range, and the T mode resonant frequency is higher than the first LT mode resonant frequency. This results in constructive interaction, thereby increasing torsional stroke and improving T mode performance.

[0039]

[0051] As is clear from Table 1, the mechanical quality factor Q Mand the effective coupling coefficient K of the OZil® assembly eff This is much lower than that of Moog LT and grooved LT assemblies. The effective coupling of Moog LT is also about half that of grooved LT. The FOM value of OZil®, which is 0.8, is significantly smaller than the FOM value of Moog LT, which is 14.5, and both are much smaller than the FOM of grooved LT, which is 47.6. Minimum impedance Z of grooved LT at T-mode resonance min (148Ω) is also the Z of OZil(registered trademark) (621Ω) and Moog LT (176Ω) min This is significantly lower. By positioning the groove 50 in an axial position corresponding to the vibration node of the first LT mode and intentionally selecting the groove depth, the grooved LT handpiece assembly achieves superior low-power T-mode performance characteristics when compared to Moog LT assemblies, and especially when compared to Alcon OZil® assemblies, due to the resonant frequency interval between the T mode and the first LT mode falling within a constructively favorable range for interaction.

[0040]

[0052] Low-power L-mode performance for all three 1 / 2-inch handpiece assemblies is similar, except for the L-mode resonant frequency, which is 41,000 Hz for the grooved LT assembly, 42,590 Hz for the Moog LT assembly, and 44,000 Hz for the OZil® assembly. The groove position and depth do not significantly affect the L-mode. Effective coupling is similar for all three, with the grooved LT assembly being the highest at 0.178. Mechanical quality factor Q for OZil®. M The value is 286, which is the mechanical quality factor Q for Moog LT and grooved LT assemblies, which is 1498 and 733 respectively. M Significantly lower than Q M and K effRegarding the combined FOM, the grooved LT assembly has the highest at 23.2, the OZil® assembly has the lowest at 6.9, and the Moog LT assembly is in between at 16.2. The OZil® assembly has the lowest L-mode minimum impedance at 61Ω, the Moog LT assembly has the highest L-mode minimum impedance at 107Ω, and the grooved LT assembly has an L-mode minimum impedance between the other two at 79Ω. While the L-mode performance is similar for all three handpiece assemblies, the grooved LT assembly has the highest FOM of the three, and both the grooved LT assembly and the Moog LT assembly have minimum impedances lower than the minimum impedance of the OZil® assembly.

[0041]

[0053] High-power testing:

[0054] Next, we compare the high-power stroke measurements in T-mode and L-mode for all three 1 / 2-inch handpiece assemblies. The high-power performance characteristics in T-mode and L-mode are listed in Table 2 below. The T-stroke and L-stroke results in Table 2 were measured at approximately 5W of power for each 1 / 2-inch handpiece assembly. Measurements shown in parentheses were scaled to exactly 5W of power for direct comparison. The same needle used for low-power testing was used for each handpiece assembly for high-power testing.

[0042] [Table 2]

[0043]

[0055] In addition to the 5W measurements that yielded the results in Table 2, high-power T-stroke and L-stroke measurements were also performed at actual power levels of approximately 10W, and at actual power levels that resulted in a T-stroke of 75μm and an L-stroke of 85μm. The plots of T-stroke versus drive voltage and T-stroke versus apparent power (V*I) from these measurements are shown in Figures 13 and 14, respectively.

[0044]

[0056] The high-power T-mode performance characteristics are similar for the Moog LT handpiece assembly and the grooved LT handpiece assembly. The drive voltage and minimum impedance are nearly identical, as are the power factor, T-stroke, and T-stroke per volt. The T-mode resonant frequency is approximately 2 kHz lower for the grooved LT assembly compared to the Moog LT assembly. To increase the T-mode resonant frequency of the grooved LT assembly to match that of the Moog LT assembly, the high-gain section 42 of the horn 12 must be shortened by 1.9 mm, and the grooved LT handpiece must be 5.9 mm (0.23 inches) shorter than the Moog LT handpiece, as shown in Figure 15. By varying the depth of the groove 50 located at the vibration node of the first LT mode, the high-power performance characteristics of the Moog LT assembly and the grooved LT assembly are equivalent, as reflected in Table 2 and plotted in Figures 13 and 14. This is achieved by using groove depth to adjust the first LT mode resonant frequency relative to the T mode resonant frequency, rather than increasing the length of the horn unity gain (low gain) section and spacer for the Moog LT handpiece assembly shown in Figure 15. The axially shortened low-gain section 40 of the horn 12 and the axially shortened spacer of the grooved LT assembly, combined with the axially shortened high-gain section 42 of the horn, the groove 50, and the use of six PZT8 ceramic rings in contrast to four PZT8 ceramic rings, result in a grooved LT handpiece assembly that has similar high-power performance to the Moog LT handpiece assembly but weighs 26.8 grams compared to 33.2 grams for the Moog LT handpiece assembly. In addition, the grooved LT handpiece assembly is 0.23 inches shorter. The significantly lighter (6.4 grams) and shorter grooved LT handpiece assembly helps reduce surgeon fatigue.

[0045]

[0057] A comparison of the L-mode high-power performance of grooved LT handpiece assemblies and Moog LT handpiece assemblies shows that the drive voltage and minimum impedance are higher for the Moog LT assembly, while the power factor is lower for the Moog LT assembly. The L-stroke is similar for both assemblies, but the L-stroke per volt is lower for the Moog LT assembly. In general, the high-power L-mode performance of the grooved LT assembly at 5W is improved compared to the Moog LT assembly.

[0046]

[0058] Comparing the T-mode high-power (5W) stroke test results of the grooved LT assembly, recorded in Table 2 and plotted in Figures 13 and 14, with the T-mode results of the OZil® assembly, the drive voltage required by the OZil® assembly is more than twice the drive power required by the grooved LT assembly to generate the same 44 μm T-stroke. The higher drive voltage and current required by the OZil® assembly stem from a much lower T-mode power factor of 0.24 for OZil® compared to 0.99 for the grooved LT assembly. The lower power factor of the OZil® assembly stems from weaker T-mode resonance and higher minimum impedance. Based on these results, as well as the low-power performance results, the T-mode performance of the grooved LT assembly is significantly improved compared to the T-mode performance of the OZil® assembly.

[0047]

[0059] The power factor of 0.6 for the OZil® assembly in L-mode is lower than the power factor of 0.9 for the grooved LT assembly in L-mode. As a result, the OZil® assembly requires higher voltage and current than the grooved LT assembly to generate 5W of actual power, and both handpiece assemblies produce nearly the same L-stroke. Based on the results presented in Table 2, the L-mode performance of the grooved LT assembly is also improved compared to the L-mode performance of the OZil® assembly.

[0048]

[0060] Although the handpiece assembly 10 of this disclosure is designed for cataract surgery, it may be adapted for use in LT handpieces used in other surgical procedures such as dental surgery, orthopedic surgery, and bone surgery, as well as in non-surgical industrial applications such as drilling (e.g., hard rock drilling), coring, and material removal. The handpiece assembly 10 of the present invention may also be applied when replacing more complex ultrasonic drills, such as those used by NASA in Mars exploration and described in U.S. Patents 6,863,136, 6,968,910, and 7,156,189.

[0049]

[0061] While this disclosure describes one or more specific embodiments, it will be understood that other embodiments of this disclosure can be made without departing from the scope of this disclosure. Therefore, this disclosure is deemed to be limited only by the appended claims and their reasonable interpretation.

Claims

1. An ultrasonic handpiece assembly, A horn that is elongated along its longitudinal axis, the horn comprising a rear end, a front end opposite to the rear end, and a horn lumen extending axially through the horn, A rear mass attached to the rear end of the horn, wherein the rear mass has a rear mass cavity that extends axially through the rear mass and communicates with the horn cavity, Multiple piezoelectric elements arranged coaxially around the horn within the stack, The stack of piezoelectric elements comprises an L-T spring coaxially arranged around the horn at the axial rear of the stack, The horn includes a low-gain section located axially forward of the stack of piezoelectric elements and a high-gain section located axially forward of the low-gain section, wherein the high-gain section has a smaller cross-sectional area than the low-gain section. The low-gain section of the horn includes a circumferential groove, The ultrasonic handpiece assembly has a first L-T mode at a first resonant frequency, a T mode at a second resonant frequency, a second L-T mode at a third resonant frequency, and an L mode at a fourth resonant frequency. An ultrasonic handpiece assembly in which the circumferential groove is positioned in an axial location corresponding to the vibration node of the first L-T mode.

2. The ultrasonic handpiece assembly according to claim 1, further comprising a needle attached to the front end of the horn, wherein the needle has a needle lumen extending axially through the needle and communicating with the lumen of the horn, and when the ultrasonic handpiece assembly is operated in the T mode, the first L-T mode torsional vibration constructively interacts with the T mode torsional vibration to increase the torsional stroke at the tip of the needle.

3. The ultrasonic handpiece assembly according to claim 1, wherein the circumferential groove has a depth such that the second resonant frequency exceeds the first resonant frequency by a frequency difference in the range of 1.3 kHz to 2.2 kHz.

4. The ultrasonic handpiece assembly according to claim 1, further comprising a spacer arranged coaxially around the horn adjacent to the rear mass.

5. The ultrasonic handpiece assembly according to claim 1, wherein the low-gain section of the horn is a unit-gain section.

6. The ultrasonic handpiece assembly according to claim 1, wherein the low-gain section of the horn is cylindrical and has a diameter of 0.375 inches (9.52 mm), and the circumferential groove has an axial length of 0.22 inches (5.588 mm) and a radial depth ranging from 0.05 inches (1.270 mm) to 0.08 inches (2.032 mm).

7. The ultrasonic handpiece assembly according to claim 6, wherein the radial depth of the circumferential groove is 0.0555 inches (1.397 mm).

8. The ultrasonic handpiece assembly according to claim 1, wherein the low-gain section of the horn is cylindrical and has a diameter of 0.5 inches (12.7 mm), and the circumferential groove has an axial length of 0.22 inches (5.588 mm) and a radial depth ranging from 0.04 inches (1.016 mm) to 0.08 inches (2.032 mm).

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