Compact Laser Steering End Effector

Abstract

The compact laser steering end effector includes a frame, at least two active mirrors, and a pair of actuators. The frame has a maximum dimension of 13 mm or less in a plane perpendicular to the longitudinal axis, and the mirrors are mounted near a distal end of the frame. The actuators are attached to the frame and configured to respectively change the tilt of the active mirrors relative to the frame. A path is provided through the frame for transmitting a laser beam to the mirrors, and the mirrors are positionable and configurable via the actuators to reflect the laser beam from each mirror toward an external target.

Description

[Technical field]

[0001] The following background description may reflect hindsight gained from the disclosed invention and those features are not necessarily admitted to be prior art.

[0002] In 2018, more than 30,000 people were diagnosed with pharyngeal or laryngeal cancer in the United States, resulting in 6,000 deaths. These cancers have a significant negative impact on quality of life, with symptoms such as dysphagia and dysphonia often leading to depression and social isolation, and curative treatments often exacerbating these functional disorders. Morbidity has increased, historically due to tobacco smoking but more recently due to the human papillomavirus, resulting in a historically younger patient population with serious concerns about long-term functional prognosis.

[0003] For this reason, there is a strong need for therapies that can preserve organ function after treatment of these cancers. Partial or total organ removal by open surgery is extreme and almost guarantees an excellent oncological outcome, but at the expense of functional outcome. Non-surgical approaches, such as induction chemotherapy, intensity-modulated radiation therapy, and concurrent chemotherapy with radiation therapy, can achieve good oncological outcomes while providing better functional outcomes than open surgery. Currently, such approaches are recommended for most laryngeal cancers. However, during the past two decades, the long-term morbidity and functional impairment associated with radiation therapy have led otolaryngologists to reconsider surgery. Minimally invasive surgery in particular has been of interest in terms of preserving more healthy tissue and improving postoperative organ function compared to open surgery. [Background technology]

[0004] Transoral laser microsurgery (TLM) is the most mature minimally invasive approach. In TLM, a carbon dioxide laser is coupled to a surgical microscope and delivered through a laryngoscope that provides visual access to the upper airway. The surgeon retracts the lesion using manual tools inserted through the laryngoscope and manipulates the laser beam using the microscope's micromanipulator to ablate the diseased tissue. In advanced systems, the micromanipulator is motorized, allowing the surgeon to deliver the laser along a predefined arc or line at a precisely controlled speed, resulting in a very high quality incision. The most significant limitation of TLM is the line of sight constraint, which limits both vision and delivery. In addition, a long and narrow laryngoscope makes manual manipulation of the tools required for retraction and suturing difficult.

[0005] To address these shortcomings, transoral robotic surgery (TORS) was developed in the mid-2000s. In TORS, flexible or articulated robotic manipulators are used in combination with an endoscopic vision system to provide superior visualization of the surgical site and tissue manipulation. Currently, the DA VINCI multiport system and the DA VINCI single port system (Intuitive Surgical Inc., Sunnyvale, CA, USA) and the FLEX robotic system (Medrobotics, Raynham, MA, USA) are in clinical use.

[0006] However, compared to TLM, TORS has the disadvantage of more severe postoperative pain and longer recovery time than similar procedures performed in TLM, due to the use of electrocautery to perform the incision. Recent developments of hollow-core fibers that allow for the delivery of carbon dioxide lasers with flexible instruments are expected to alleviate this issue to some extent and increase the use of lasers in TORS. However, because fiber-based lasers are held and manipulated by robotic tools, they lack the spatial repeatability, precision, and speed of free-beam scanning systems. This means that the quality of the incision is reduced compared to the free-beam systems used in TLM. Free-beam systems have the added advantage of keeping the surgical site clear and visualizing the exposure and margins.

[0007] Many prototype endoscopic devices have been developed for minimally invasive laser scanning tasks, each employing a different approach to the challenging design challenge. S. Patel et al., "Endoscopic laser scalpel for head and neck cancer surgery," Photonic Therapeutics and Diagnostics VIII, Vol. 8207, International Society for Optics and Photonics 82071S (2012) uses a DC motor-driven Risley prism as the beam steering scheme, allowing for an easy-to-implement control scheme, but the scanning speed is very limited (2 Hz). O. Ferhanoglu et al., "A 5-mm piezo-scanning fiber device for high speed ultrafast laser microsurgery," Biomedical Optics Express, Vol. 5, No. 7, 2023-2036 (2014) uses a piezoelectric actuator to directly bend the optical fiber, achieving a wide bandwidth (1 kHz) with a thin device profile (5 mm diameter), but resulting in a reduced field of view (200 × 200 μm). A. Acemoglu et al., "Design and control of a magnetic laser scanner for endoscopic microsurgeries," IEEE / ASME Transactions on Mechatronics (2019), used electromagnets to bend the fiber, increasing the range of motion to 3 × 3 mm, but doing so at the expense of bandwidth (15 Hz).Finally, R. Renevier et al., "Endoscopic laser surgery: design, modeling and control," IEEE / ASME Transactions on Mechatronics, Vol. 22, No. 1, 99-106 (2017) describes how the FEMTO-ST laboratory developed a system using off-the-shelf piezoelectric linear actuators to articulate a silicon mirror held on a tip-tilt stage, achieving a field of view of 20 × 20 mm at a low scanning speed (17 Hz). Summary of the Invention

[0008] Described herein is a miniature laser steering end effector and a method of using the end effector, particularly for surgery, various embodiments of the apparatus and method may include some or all of the elements, features and steps described below.

[0009] The compact laser steering end effector includes a frame, at least two active mirrors, and a pair of actuators. The frame has a maximum dimension in a plane perpendicular to the longitudinal axis of the frame of 13 mm or less, and the mirrors are mounted proximate to a distal end of the frame (i.e., closer to the distal end than to the proximal end of the frame). The actuators are mounted to the frame and configured to respectively vary the tilt of the active mirrors relative to the frame. A path is provided through the frame for delivering a laser beam to the mirrors, and the mirrors are orientable and configurable via the actuators to reflect the laser beam from each mirror en route to an external target.

[0010] In a method of robotic laser steering, a laser beam is generated and directed at a proximal end of an end effector to a region proximal to the distal end of the end effector, where the laser beam is reflected off at least two active mirrors, and an actuator is used to change the tilt direction of the at least two active mirrors to move the laser beam across a target.

[0011] The device and method described herein can incorporate the advantages of both TLM and TORS in a laser scanning system operating at the end of a robotic manipulator. The device and method can enable more precise dissections and correspondingly less tissue damage than existing laser or electrocautery tools. Furthermore, moving the laser fiber within the robotic manipulator can relax the constraints on fiber design and use, which is advantageous considering that currently available CO2 laser fibers are expensive (~1,000 USD) and single-use. Below, we describe a prototype device to realize this TLM / TORS hybrid paradigm.

[0012] In recent years, minimally invasive surgical techniques have emerged that can preserve more healthy tissue, but they are still limited in important respects. Here, we describe a device that can combine the advantages of two of the existing major minimally invasive approaches: (a) the high-quality incisions and reduced postoperative pain achievable with transoral laser microsurgery, and (b) the excellent visualization and tissue manipulation offered by transoral robotic surgery. In our example, an 11 mm diameter device is connected to a fiber-optic laser source, delivering a laser beam focused in an 18 × 10 mm plane with a controllable trajectory at a speed of up to 7 m / s.

[0013] By combining the advantages of TORS and TLM, this approach is expected to improve the quality of treatment for pharyngeal and laryngeal cancers. This allows for better access and exposure than TLM alone, and a higher quality of incision than TORS alone. This results in a streamlined procedure for the surgeon and improved functional outcomes for the patient. Other applications of this approach include laser-assisted cardiac ablation, laser-assisted gastrointestinal surgery, laser-assisted abdominal surgery, and laser-assisted transnasal skull base surgery.

[0014] The end effectors described herein can be precisely actuated at high speed, enabling important new methods of robotic interaction with biological tissue. In particular, the end effectors can be incorporated into microrobotic devices to achieve deft control of laser energy in minimally invasive surgery. The high bandwidth distal actuation achieved by these devices and methods can be integrated with existing surgical tools to precisely control the position of fiber-delivered lasers. The manufacturing and modular assembly approach described herein can create significantly smaller devices with higher bandwidth than the current state of the art, while achieving a similar range of motion as existing tools. For example, the device can be 6 mm or smaller in diameter and 16 mm or smaller in length, and can focus and steer fiber-delivered laser beans at high speeds (e.g., 1.2 kHz bandwidth) over a wide range (e.g., ±10° in both axes) with excellent static repeatability (e.g., ±200 μm). This approach allows precise control of laser speed, and therefore energy delivery time, over a wide range, thus providing greater control of energy delivery in surgery than existing rigid cable-driven tools. Such a dexterous energy delivery approach can be deployed in a variety of surgical areas where controllable energy is required in limited spaces. [Brief description of the drawings]

[0015] [Figure 1]1 shows a first embodiment of an end effector 10 of a laser scanning system for use in transoral robotic surgery. The end effector 10 receives a fiber input and manipulates a focal spot on a surgical surface. [Diagram 2] FIG. 2 is a long exposure photograph showing a typical cut profile used in laser-based tissue ablation using the end effector design of FIG. [Diagram 3] FIG. 3 is a long exposure photograph showing a typical cut profile used in laser-based tissue ablation using the end effector design of FIG. [Figure 4] FIG. 4 is a perspective view of a second embodiment of a miniature laser steering end effector 10 for robotic surgery. [Diagram 5] FIG. 5 is an end view of the miniature laser steering end effector 10 for robotic surgery shown in FIG. [Figure 6] FIG. 6 is a side view of the miniature laser steering end effector 10 for robotic surgery shown in FIGS. [Figure 7] FIG. 7 is a perspective view of the miniature laser steering end effector 10 for robotic surgery shown in FIGS. 4-6, including an exploded view of various portions of the end effector 10. [Figure 8] FIG. 8 is a perspective view of a first embodiment of a laser scanning end effector 10 defining the location of the major subsystems. [Figure 9] Figure 9 shows the optical subsystem 48 of the end effector 10 of Figure 8. The optical subsystem 48 connects a fiber optic light source to a laser scanner. [Figure 10] FIG. 10 shows an actuation subsystem 50 of the end effector 10 of FIG. 8, which includes the piezoelectric bending actuators 18 and 22 and a rigid mechanical frame (base) 40 that aligns the optics with the rest of the apparatus. [Figure 11] FIG. 11 shows the mirror subsystem 52 of the end effector 10, including the motion transfer linkage 38 and the flat active mirrors 28 / 30. [Figure 12]FIG. 12 shows the crank-slider transmission motion, shown diagrammatically with the design values ​​selected from the table. [Figure 13] Figure 13 is a diagram of the crank-slider arm on the fabricated linkage of the first embodiment of the end effector. Figure 13 shows the first mirror linkage 38. The first set of solid lines 71 indicate the active link of the crank-slider, the dotted lines 73 represent the axis of rotation of the crank, and the second set of solid lines 75 indicate the physical parts that are bent back to facilitate assembly of the linkage 38. The joints are represented by the black circles 77, and the translation of the slider and rotation of the crank are represented by the dotted black trajectories 79. [Figure 14] Figure 14 is a diagram of the crank-slider arm on the fabricated linkage of the first embodiment of the end effector. Figure 14 shows the second mirror linkage 38. The first set of solid lines 71 indicate the active link of the crank-slider, the dotted lines 73 represent the axis of rotation of the crank, and the second set of solid lines 75 indicate the physical parts that are bent back to facilitate assembly of the linkage 38. The joints are represented by the black circles 77, and the translation of the slider and rotation of the crank are represented by the dotted black trajectories 79. [Figure 15] FIG. 15 is a schematic diagram of a laser scanning system with key symbols defined thereon. [Figure 16] 16 shows the linkage fabrication process.FIG 16 shows the individual layers of rigid material 60, flexible material 62, and adhesive 64 that were cut using laser micromachining. [Figure 17] 17 shows the linkage fabrication process.Figure 17 shows the layers 60, 62 aligned over the pins 68 and laminated together using heat and pressure 66 from a lamination plate. [Figure 18] 18 shows the linkage fabrication process.In Fig. 18, further laser micromachining is performed to create the linkage 38 structure of the first embodiment of the end effector. [Figure 19] 19 shows the linkage fabrication process.In Fig. 19, the linkage structure 38 is partially deployed after releasing the assembly tabs. [Figure 20]20 shows the linkage fabrication process. In Fig. 20, a 3D printed assembly jig 70 is used to bend the linkage arms into the desired positions. [Figure 21] 21 illustrates the linkage fabrication process.In Fig. 21, the last tab is released and the linkage 38 is ready to be integrated with the rest of the device. [Figure 22] FIG. 22 plots the measured mirror angles as a function of actuator voltage for the first mirror 28″ and second mirror 30″ of the first embodiment of the end effector. The overall trend is well captured by the theoretical model of the first mirror 28′ and second mirror 30′, with mean absolute errors of 0.6° and 1.2° for the first and second mirrors, respectively. [Figure 23] FIG. 23 is a plot of the frequency response of the actuator-transmission-mirror subsystem for the first linkage actuator 18 and the second linkage actuator 22 of the first embodiment of the end effector. [Figure 24] 24 shows the laser spot position tracking setup for the first embodiment of the end effector as viewed by a high speed camera. The theoretical field of view 72 and the achieved field of view 74 from a standoff distance of 20 mm are shown. [Diagram 25] Figure 25 shows the profiles drawn at different speeds using the first embodiment of the end effector, demonstrating the open-loop trajectory following capability of the laser scanner. The high-speed performance of the system is demonstrated through its repeatability over a range of commanded speeds. [Figure 26] FIG. 26 shows three mirror angle configurations of a three-mirror galvanometer. [Figure 27] FIG. 27 shows two mirror angle configurations of a two-mirror galvanometer. [Figure 28] FIG. 28 shows two additional mirror angle configurations for a two-mirror galvanometer. [Figure 29] FIG. 29 shows a first active mirror 28 and associated actuator 18 and passive transmission linkage 38 of a second embodiment of the end effector. [Diagram 30]FIG. 30 shows a second active mirror 30 and associated actuator 22 and passive transmission linkage 38 of a second embodiment of the end effector. [Diagram 31] FIG. 31 shows the modular components of a second embodiment of a laser steering end effector. [Diagram 32] FIG. 32 is a plot of the frequency response, in terms of phase and amplitude, respectively, of the first and second mirrors of the second embodiment of the end effector. [Diagram 33] FIG. 33 is a plot of the frequency response, in terms of phase and amplitude, respectively, of the first and second mirrors of the second embodiment of the end effector. [Diagram 34] FIG. 34 is an image produced by high speed movement of the laser steering system of the second embodiment of the end effector. [Diagram 35] FIG. 35 shows how the high speed images (generated at 3,900 mm / sec) closely match the trajectory generated at low speed (7.8 mm / sec) by the laser system of the second embodiment of the end effector.

[0016] In the accompanying drawings, like reference characters refer to the same or similar parts throughout the different views. The drawings are not necessarily to scale, but rather the emphasis is on illustrating certain principles as described below. For drawings that include text (words, reference letters, and / or numbers), alternative versions of the drawings that do not include the text should be understood to be part of this disclosure, and formal alternative drawings without such text may be used instead. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] These and other features and advantages of various aspects of the present invention will become apparent from the following detailed description of various concepts and specific embodiments within the broad scope of the present invention. The various aspects of the subject matter introduced above and discussed in more detail below can be implemented in any of many ways, and the subject matter is not limited to any particular implementation. Specific implementations and applications are provided primarily for illustrative purposes.

[0018] Unless otherwise defined, used, or characterized herein, terms (including technical and scientific terms) used herein should be interpreted to have meanings consistent with those accepted in the context of the relevant art, and not to be interpreted in an idealized or overly formal sense unless expressly defined. For example, when referring to a particular composition, the composition may be substantially (though not completely) pure, although practical and imperfect realities may apply. For example, the potential presence of at least trace amounts of impurities (e.g., less than 1 or 2%) may be understood to be within the scope of the description. Similarly, when referring to a particular shape, the shape is intended to include imperfect variations from the ideal shape, for example, due to manufacturing tolerances. Percentages or concentrations expressed herein may be weight or volume ratios. The processes, procedures, and phenomena described below may occur at atmospheric pressure (i.e., for example, about 50-120 kPa, about 90-110 kPa, etc.) and temperature (i.e., for example, -20-50°C, about 10-35°C, etc.) unless otherwise specified.

[0019] In this specification, the terms first, second, third, etc. are used to describe various elements, but these elements are not limited by these terms. These terms are used merely to distinguish one element from another element. Thus, a first element described below can also be called a second element without departing from the teachings of the exemplary embodiments.

[0020] Spatially relative terms such as "top", "bottom", "left", "right", "front", "back" and the like may be used herein to describe the relationship of one element to another for ease of description, as shown in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device during use or operation in addition to the orientation described and illustrated herein, as well as the configurations depicted. For example, if the device in the figures is inverted, elements described as "below" or "beneath" other elements or features will be oriented "above" the other elements or features. Thus, the exemplary term "top" may encompass both an orientation of above and below. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptions used herein may be interpreted accordingly. The term "about" may mean within ±10% of the stated value. Additionally, when a range of values ​​is provided, each subrange and each individual value between the upper and lower limits of the range is contemplated and therefore disclosed.

[0021] Additionally, in this disclosure, when an element is referred to as "on," "connected," "coupled," "in contact," or the like, to another element, unless otherwise specified, it may be directly on, connected, coupled, or in contact with the other element, or there may be intervening elements present.

[0022] The terms used herein are intended to describe particular embodiments and are not intended to limit the exemplary embodiments. As used herein, the singular forms such as those introduced by the articles "a" and "an" are intended to include the plural forms unless the context indicates otherwise. Furthermore, the terms "comprise", "includes", "comprises" and "comprising" specify the presence of a stated element or step, but do not exclude the presence or addition of one or more other elements or steps.

[0023] Additionally, the various components identified herein may be provided in a fully assembled form, or some or all of the components may be packaged together and sold as a kit that includes instructions (e.g., in written, video, or audio form) for a customer to assemble and / or modify to create a finished product.

[0024] Minimally invasive surgery allows access to internal anatomical structures through natural orifices or small external incisions. This includes procedures as diverse as catheter delivery of stents (angioplasty), flexible endoscopy of the gastrointestinal tract, laparoscopic treatment of abdominal disease, and transnasal skull base surgery for neurological conditions. Common to many of these procedures is the need for a wrist joint at the distal end of the tool to manipulate tissue and visualize the surgical site. The need for this joint was a key motivation for the introduction of robotics into minimally invasive surgery and remains a subject of active research and development.

[0025] Proximal actuation cable-transmitted approaches have prevailed for achieving wrist joint motion due to significant size constraints imposed by access methods and anatomical size. However, the drawbacks of cable actuation are well known, with output power limited by the allowable tension in the cable and bandwidth limited by the mass and elasticity of the series elastic and backlash-suppressing preload components. These constraints have motivated significant research efforts to develop novel distal actuation mechanisms actuated by other means, such as shape-memory actuators, pneumatic fluids, and flexible rods, that achieve dexterity without the constraints of cable actuation.

[0026] This paper focuses on a subset of instruments used in minimally invasive surgery, specifically tools used for energy delivery. Common surgical energy sources include monopolar and bipolar radiofrequency current (electrosurgery), thermal cauterization (direct current heating), ultrasonic vibration, argon beam coagulation (argon assists in conducting radiofrequency current), and lasers. These tools are essential to the surgical workflow as they allow for cutting, coagulation, desiccation, and carbonization of tissue deep within the body. These different energy sources ultimately result in the same effect: denaturation of proteins through heating of tissue. Furthermore, these energy sources are currently used in similar ways. Specifically, the energy source is brought close to the tissue (e.g., within a few millimeters) and energy is delivered directly from electrodes or fibers to the anatomical structure being treated.

[0027] However, more sophisticated approaches to laser energy delivery are possible. While current laser-based instruments are used in a static, tight-fitting manner, dynamic approaches could be employed using miniature laser galvanometers as a wrist to manipulate the laser energy. Because the laser can be focused and steered using low-inertia optics, high-bandwidth distal actuation can be utilized to control the laser position. This provides the same benefits that a robotic wrist gives to a mechanical end effector (i.e., the ability to maneuver around corners and obstacles), while providing the added ability to precisely control the laser velocity on the tissue over a wide range. This is important because laser velocity strongly influences the duration of laser exposure, which is a key factor in determining the quality of the laser-tissue interaction in terms of incision depth, spread of thermal damage, and hemostatic efficacy.

[0028] The challenge in creating this type of robotic device is the required optical, electrical, and mechanical complexity in a small package. The diameter of the device is a key constraint and varies with the type of surgical instrument used. Examples of commonly used tools span a range of sizes: colonoscopes ranging from 9.7 to 14.8 mm (e.g., PCF-PH190I / L and CF-FH260AZI / L from Olympus Medical Systems), laparoscopic tools ranging from 5 to 8 mm (e.g., da VinciSP from Intuitive Surgical), transnasal access rhinoscopes ranging from 2.6 to 4.9 mm (e.g., ENF-V3 and ENF-VT3 rhinoscopes from Olympus Medical Systems), and cardiac catheters ranging from 2.67 to 3.33 mm (e.g., AcuNav catheter from Biosense Webster).

[0029] Using breakthroughs in millimeter-scale design and manufacturing, we demonstrate how microrobotic laser beam steering can be integrated with a subset of these tools. Our approach builds on recent advances in robotics and medicine, leveraging millimeter-scale actuators and sensors to achieve more precise control of tools and manipulation of tissue. This example laser steering solution is 6 mm in diameter and can therefore be seamlessly integrated into existing workflows for flexible gastrointestinal surgery and single-incision laparoscopic surgery. In this setting, lasers have been particularly important, as traditional tools are difficult to adapt.

[0030] An end effector with microrobotic laser beam steering can be integrated with surgical instruments such as a colonoscope (Olympus CF-100L). The end effector can be mounted externally to the surgical instrument or is small enough to be integrated internally into special purpose flexible scopes. The device is 16 mm long and has the capability to steer a focused laser beam over ±10° on two orthogonal axes with a mechanical bandwidth of 1.2 kHz.

[0031] The performance achieved represents a significant improvement over current technologies, which tend to be bulky and slow. All of these solutions are larger than 1 cm in diameter and longer than 2 cm in length. These devices achieve a similar range of motion to ours, but at the expense of speed due to the actuators and their mechanics. In contrast, our approach uses piezoelectric bending actuators operating through a flexure transmission to generate rotational motion of a low-inertia mirror. This allows for a mechanical bandwidth that is 1-2 orders of magnitude larger than current technologies, as well as superior repeatability (i.e. precision).

[0032] Here we describe significant advances in design, fabrication, and control that enable us to exceed the performance of state-of-the-art devices. These include the general principles for building a miniature laser galvanometer as well as the specific design details of the device. Our approach separates the device into modules (lenses, actuators, mirrors, etc.), each verified individually before mounting them to the disk and assembling them onto a railed superstructure that serves as a common mechanical ground, minimizing the number of assembly parts and facilitating alignment of critical components. On the fabrication side, lamination techniques can be used to create miniature compliant mechanisms capable of generating large-angle mirror rotations without sacrificing miniaturization. On the control side, we can employ piezoelectric bending actuators and low-order hysteresis compensation schemes to compensate for hysteresis in the intermediate mechanism.

[0033] A laser scanning system including a miniature laser steering end effector 10 for use in transoral robotic surgery is shown in FIG. 1. The device receives laser input from an optical fiber 12 and steers a focused spot on the surgical surface. The device may include two lasers including a low powered navigating laser that illuminates the internal cavity to aid in visualization and navigating the end effector to the desired location, and a high powered surgical laser for cutting tissue. The laser passes from the optical fiber 12 through a collimator 14 to a mechanical structure 16, which includes a first linkage actuator 18 configured to displace a first link mirror assembly 20 and a second linkage actuator 22 configured to displace a second link mirror assembly 24. FIGS. 2 and 3 are long exposure photographs showing a typical cut profile used in laser-based tissue ablation.

[0034] As shown in Figures 4-11, recently developed microfabrication techniques P.S. Sreetharan et al., "Monolithic fabrication of millimeter-scale machines," Journal of Micromechanics and Microengineering, Vol. 22, No. 5, 055027 (2012) can be used to create a miniature mechanical passive transfer linkage 38 that converts the quasi-linear motion of high bandwidth piezoelectric bending actuators 18 and 22 into a rotational motion that is used to orient mirrors 28 and 30 that receive the laser beam after reflection of the beam from a fixed mirror 42. An example of this device includes two such actuator-transmitter-mirror combinations arranged orthogonally such that the two actuation inputs from actuators 18 and 22 correspond to orthogonal ablation of the target tissue. The light is transmitted to the laser scanner using an optical fiber in the laser entrance conduit 36, where the output is fed as a free beam (no longer in the fiber) to an assembly of a gradient index collimating lens 32 and a miniature plano-convex focusing lens 34. This free, focused beam is then steered by rotating two active mirrors 28 and 30 using a crank-slider transmission to translate linear actuator motion from an actuation subsystem 50 (FIG. 10) into the desired rotational motion. The scan frame 40 (including a rigid disk platform 92 slidably mounted on a rigid rod 94) provides a mechanical ground for the actuators 18 and 22 and transmission 38, as well as ensuring precise alignment between the optical subsystem 48 (FIG. 9) and the mirror subsystem 52 (FIG. 11).

[0035] As shown in FIGS. 4-7, the end effector 10 can include two actuators 18 and 22 in the form of piezoelectric bimorph cantilevers 18 and 22, as described in U.S. Pat. No. 9,038,942 B2 (Harvard).

[0036] Piezoelectric bimorph cantilevers 18 and 22 can be fabricated via smart composite microstructure manufacturing techniques, as described in R. Wood, "The First Takeoff of a Biologically Inspired At-Scale Robotic Insect," IEEE Transactions on Robotics, 24(2), 341 (2008). First, individual thin layers (e.g., PbZrTiO3 (PZT)-5H piezoelectric layers and M60J carbon fiber / cyanate ester resin prepreg layers) are laser micromachined into the desired link shape. These layers are then stacked and aligned and subjected to a controlled cure cycle that regulates temperature, pressure, and cure time. The resulting actuators 18 and 22 are each fixed proximally to a frame 40 (including a plurality of rigid plates 92 mounted along a plurality of rigid rods 94) and distally to a passive transfer linkage 38 which provides a transfer structure for translating the bending displacement of the cantilever actuators 18 / 22 to adjust the tilt of one of the active mirrors 28 / 30 to direct the reflection of the laser towards a desired target. A voltage source is also coupled to the actuators 18 / 22 such that application of a voltage to either of the piezoelectric layers causes the actuators 18 / 22 to bend.

[0037] The coupling of one of the pathway transfer linkages 38 to one of the active mirrors 28 / 30 is shown in Figure 11. The mirrors 28 / 30 are mounted for rotation about a rotation pin 44 attached to a rigid mount extending from a mechanical ground plate 54 in the frame, such that rotation of the rotation pin 44 in the rigid mount via displacement of the passive linkage 38 produces a change in the tilt angle of the active mirror 28 / 30.

[0038] Design requirements are derived from the envisioned surgical environment. A target field of view of 10 × 20 mm is selected according to the nominal size of the vocal cords. An upper limit on the device diameter was selected at 13 mm to allow space for retraction tools, visualization, and illumination. A standoff distance of 20 mm was selected to balance the needs for visualization and tissue manipulation while minimizing the scanning system's angle of view. Finally, a target spot size of 250 μm and a target surface speed of 100 mm / s were selected according to the scanning system used in TLM.

[0039] A variety of lasers are used in laryngeal surgery, including CO2, potassium titanyl phosphate (KTP), and diode lasers. Although CO2 lasers are the preferred choice in many situations, optical fibers delivering this wavelength at high power tend to have large core diameters, which result in spot sizes that exceed the design requirements. Therefore, a prototype was designed using a 35 μm core PM780-HP fiber from Nufern Inc. for use with a diode laser capable of delivering high power (60 W). However, this prototype used a low-power optical fiber inspection laser to verify its mechanism. A collimator with a focal length of 6.17 mm and a focusing lens of 38.1 mm were selected to obtain a spot diameter of 210 μm when combined with an optical fiber with a core diameter of 35 μm and a numerical aperture of 0.12. Both lenses are aspheric plano-convex to reduce aberrations. The mirror sizes of 2 × 2 mm and 2 × 5 mm and an initial angle of 40° were selected according to the kinematic analysis described below. Although the size of the device is increased, we chose to use an off-the-shelf, factory-aligned fiber-coupled collimator (Thorlabs F110FC-633) for ease of integration.

[0040] The actuator lengths were chosen to be 10.6 mm and 12.1 mm to achieve adequate displacement without significantly lengthening the device. The transmitted stiffness was assumed to be approximately equal to the actuator's output stiffness, which means that the actuator deflection is reduced to one-half of the free deflection. Under this assumption, the actuator deflection at 200 V (the upper limit of the operating voltage to avoid damage to the piezoelectric ceramic actuator material) is ±200 μm and ±220 μm, respectively.

[0041] Using the optical model above, and taking into account the placement of the mirrors to minimize the diameter of the device, it was determined that advantageous ranges of motion were ±10° for the first mirror and ±15° for the second mirror. To generate these motions, the link lengths of the crank-slider shown in Figure 12 were selected according to the following crank and slider annulus shapes (link (a) is 2 mm long for both mirrors, and link (d) is 0.9 mm long for the first mirror and 0.6 mm long for the second mirror). TIFF0007660917000001.tif26170 Here, θ0 is the initial angle of the crank slider, Δ x is the actuator deflection, and x0 is the initial distance between the slider and the pivot. The initial angle θ0 is 70° for the first mirror and 75° for the second mirror. Of the two links, the length of the crank arm has the greatest effect on the output motion, and the smaller it is, the larger the output motion and therefore the larger the transmission ratio. The initial angle of the mechanism is also important, which trades off symmetry and output amplitude. We selected a linkage configuration that achieved the desired range of motion while minimizing asymmetry. The fabricated linkages are shown in Figures 13 and 14.

[0042] Given the mirror angles determined by the crank-slider relationship, expressed as Equation 1, the position of the laser spot on the target plane can be found using the vector formulation of specular reflection. The symbols and geometric definitions used are given in the system schematic shown in Figure 15, which shows the trajectory of the laser beam 46 reflecting off the first mirror 28 and the second mirror 30 onto the target plane 58. The jth basis vector of the ith coordinate system is TIFF0007660917000002.tif10170 For the i-th frame, the point p j From point p k The unit vector pointing to is TIFF0007660917000003.tif10170 The orientation of the jth coordinate system relative to the ith coordinate system. The basic rotation of angle θ around the i-axis. H y is the Householder transformation around the y-axis.

[0043] The orientation of the mirror in 3D space is given by the following formula: TIFF0007660917000004.tif22170 Here, θ 1,0 is a design variable that indicates the initial orientation of the first mirror. Here, the beam 46 reflected from the first mirror 28 has the following direction: TIFF0007660917000005.tif12170 The beam 46 then travels a distance d 12 After passing through the first mirror 30, the first mirror 30 intersects with the second mirror 30. TIFF0007660917000006.tif13170 Therefore, the position p2 of the laser beam 46 on the second mirror 30 is given by: TIFF0007660917000007.tif17170 Similarly, the reflected beam 46 from the second mirror 30 has the following direction: TIFF0007660917000008.tif13170 The following distance d 2t It later intersects with the target plane 58 . TIFF0007660917000009.tif13170 Finally, the position of the laser spot on the target plane p t is calculated by the following formula: TIFF0007660917000010.tif17170

[0044] The fabrication process used to produce the transmission linkage is based on the approach developed in P.S. Sreetharan et al., "Monolithic fabrication of millimeter-scale machines," Journal of Micromechanics and Microengineering, Vol. 22, No. 5, 055027 (2012), and is shown in Figures 16-21. Individual layers of rigid material 60 (e.g., steel), more flexible material 62 (e.g., polyimide), and adhesive 64 (e.g., acrylic adhesive) are cut using a 7W, 355nm DPSS laser micromachining system (Oxford Laser E Series) and then aligned and set into a heated press (whose bottom plate 66 is shown in Figure 17) to bond layers 60, 62, and 64 together. The bonded laminate is removed from the press and a preliminary release cut is made, as shown in Figure 18. The laminates are then bent into their desired configuration, as shown in Figure 19. The first mirror transmission is bent to the correct angle with the use of an assembly jig 70 as shown in FIG. 20, while the second mirror utilizes alignment pins used for lamination. Cyanoacrylate (CA) adhesive is then used to lock the stack in an aligned configuration and a final cut is performed to release it to the desired degree of freedom. Each linkage 38 is placed under a confocal microscope and its functional dimensions are measured to verify the process. The fabrication of the linkages 38 is a highly repeatable process with a standard deviation of less than 4% of the desired value across all 12 linkages constructed, which corresponds to a 5% variation in the linkage transmission ratio. The laminated transmission linkage 38 will bend (close to pivoting) in the longitudinal gap between the rigid links where the flexible material is exposed.

[0045] The short link length of the crank slider makes it difficult to assemble, but by bending the physical arm back to create a virtual link (as shown in Figures 13 and 14), it becomes much easier to handle. Furthermore, with this approach, the bending angle of the flexure is zero at rest and remains within the elastic deformation region.

[0046] The ground connection of the linkage is attached to a base structure of 7075 aluminum alloy fabricated on a 5-axis CNC machine (Bridgeport, Hardinge, Inc.). The mirrors were laser cut from 100 μm thick fused silica wafers (Denton Vacuum Desktop Pro) sputtered with aluminum. A protective gel layer was added on top of the mirror to protect the reflective coating during assembly. The linkages were then bonded to their respective actuators before being inserted into the mechanical structure and fixed in place with alignment pins and a press-fit plate. The actuator bases and the transmission ground linkage were then glued to the mechanical structure with cyanoacrylate adhesive. Finally, the protective gel layer was removed from the mirror with a tension to complete the fabrication.

[0047] To validate the crank slider kinematic model (Equation 1), the mirror angle and actuator displacement were measured as a function of actuator voltage. The mirror angle was measured with a high magnification inspection camera (Pixelink PIXELINK PL-B741F) at a static voltage input, while the actuator displacement was measured with a laser Doppler vibrometer (Polytec GMBH PSV-500 Vibrometer) at a quasi-static cyclic input of 1 Hz. In Figure 22, the measured 28” / 30” and predicted 28’ / 30’ mirror angles are plotted as a function of actuator input, along with the theoretical values ​​derived from the measured actuator displacements at specific voltages. The results show that the model captures the wide range of behavior of the linkage well. The mean absolute errors of the measured data were 0.6° and 1.2° for the first mirror 28” and the second mirror 30”, respectively.

[0048] To find a safe boundary for the input drive frequency, a frequency analysis was performed on both the motion actuator-transmitter-mirror subsystems. The same laser Doppler vibrometer was used to collect data under low voltage, white noise input. The results are shown in Figure 23. As expected, both subsystems are approximated as second order linear systems. The resonant frequencies are 850Hz and 750Hz, which is consistent with physical intuition. The actuator free beam resonance (1.6kHz) is reduced due to the increased mass of the transmitter.

[0049] To verify the beam steering capabilities of the device, a bench-top scanning arena was created incorporating a calibrated high-speed camera (Vision Research, Inc. PHANTOM V710 camera) with a 200 mm macro lens and two non-flickering flood lights, all mounted on an optical table. The camera view is shown in FIG. 24 along with a grid 75 used for image alignment. One pixel corresponds to 50 μm in the image plane. The device was fixed to the optical table with a defined standoff distance of 20 mm from the target.

[0050] The scanner was then calibrated by sweeping the voltage space and tracking the position of the laser spot. The overall achieved field of view 74 matches well with the model predictions 72, as shown in Figure 24. However, a slight warp was introduced in the laser task space due to unmodeled compliance of the system and misalignment of the assembly. Rather than adding degrees of freedom to the model and calibrating it, we opted to use a lookup table approach to control the position of the laser spot.

[0051] This approach yielded reasonable results in task-space-trajectory tracking, as shown in Figure 25, where the desired trajectory is shown in plot 76. Three shapes were drawn at various speeds: "H" (left), "star" (center), and Lissajous figure (right) (100 mm / s shown in plot 78, 1 m / s shown in plot 80, 2 m / s shown in plot 82, 3 m / s shown in plot 84, and 7 m / s shown in plot 86). Each shape is shown at a base speed of 100 mm / s (78) and at the highest speed that can be reproduced before vibrations in the transmission impair the tracking performance of the device. Such vibrations are visible at 2 m / s (plot 82) for the "H" trajectory. Of the three shapes, the "H" is the most challenging shape due to the abrupt changes in the trajectory. The Lissajous figure is the simplest, with little degradation in performance up to 7 m / s (plot 86), because the actuator drive voltage is smooth and approximately sinusoidal.

[0052] This prototype device meets most of the design requirements: field of view (slightly less than 10 x 20 mm), scanning speed (up to 7 m / s), and scanner size (11 mm). The combination of assembly misalignment and unmodeled off-axis compliances introduces errors into the model of the laser spot location, as shown by the resulting field of view distortion in Figure 24. This can be improved by minimizing the amount of manual manipulation required for assembly and using other bending materials or geometries with more appropriate compliance ratios.

[0053] While calibration and feedforward control allow for qualitative trajectory tracking, significant deviations from the desired trajectory remain because the calibration is performed statically and does not capture dynamic, non-linear, or hysteresis effects. Thus, feedback control may be required to precisely control the position of the laser spot. Therefore, embodiments of the present device may incorporate angle sensing at the mirror output or a means to directly feed back the laser position to a controller.

[0054] Another important next step is the integration of high magnification optics, for which higher quality mirror coatings can be incorporated. Among the available mirror coatings, gold is an advantageous option due to its high reflectivity (>97%) at the favorable wavelengths of 800-1000 nm. Dielectric coatings are also worth considering, as their reflectivity reaches up to 99.8%, but are more selective with respect to wavelength.

[0055] The mechanical structure of the mirror and linkage are somewhat fragile and can be enclosed to protect them, and the mirror can be protected from fluid flow at the surgical site.The device can be used with existing transoral robotic tools for visualization and tissue retraction, allowing for coordination of tasks with these tools.

[0056] In various embodiments, a gradient index collimating lens collects light from a ferrule-terminated optical fiber and directs it to a small plano-convex focusing lens. The light is reflected off a 45° angle of incidence mirror and into a small two-mirror galvanometer. A flexible linkage converts the quasi-linear motion of the piezoelectric bending actuator into rotational motion of the galvanometer mirror. The cylindrical profile allows for easy integration with existing surgical instruments.

[0057] In the following, we present the design, manufacturing, and control considerations culminated by this laser steering solution. First, we discuss the general design considerations for miniaturizing the galvanometer portion of the device, which is the easiest component to miniaturize from both a design and manufacturing perspective. Second, we present the design and construction of each component and their assembly details. Third, we report the methods used for static position control and characterization. Finally, we discuss the dynamic characteristics of the device, demonstration of high bandwidth operation, and interfacing the device with a commercial colonoscope.

[0058] The galvanometer is the most complex component of the device to miniaturize in design, but there are some general insights that guide our efforts with respect to the design space. The objective is to minimize the distance between the mirrors, given the beam size, mirror size, and desired range of motion, while avoiding collisions between the mirrors and between the reflected beam and the previous mirror in the optical path (see Figures 26-28). An important high-level design consideration is the number of mirrors used. Counterintuitively, a three-mirror design can actually be smaller than a two-mirror design if the same range of motion is required for each.

[0059] First, consider the three mirror designs shown in the three configurations in FIG. 26. An incident beam enters from the left and is then reflected in sequence to a fixed mirror 42, a first active mirror 28, and a second active mirror 30 (circumscribed diameter 4 mm). In the left diagram, the first and second active mirrors 28 and 30 are rotated +10°. In the middle diagram, the first active mirror 28 is rotated +10° and the second active mirror 30 is rotated -10°. In the right diagram, the first active mirror 28 is rotated -10° and the second active mirror 30 is rotated +10°. If the distance between the fixed mirror 42 and the first active mirror 28 is too small, the reflected light from the second active mirror 30 will intersect with the fixed mirror 42. If the distance between the first active mirror 28 and the second active mirror 30 is too small, the mirrors will collide. However, increasing the distance between the mirrors not only increases the size of the device, but also means that larger area mirrors are required to collect the reflected light with the same range of motion. The three-mirror design shown balances all these considerations, resulting in a device with a 4mm diameter footprint and a ±10° range of motion for each active mirror. It is also worth noting that chamfering the corners of the mirrors increases the range of motion, preventing collisions at critical locations.

[0060] The first two-mirror design (shown in two configurations in Fig. 27) has the same diameter footprint as the three-mirror design, but its range of motion is halved at the first mirror axis. In the left image, the first active mirror 28 rotates at an angle of +5° while the second active mirror 30, with a circumscribed diameter of 4 mm, is at a neutral angle of 0°. In the right image, the first active mirror 28 rotates at -5° and the second active mirror 30 is at a neutral angle of 0°. It is the result of a series of trade-offs: if the mirrors 28 and 30 (both active) are too close to each other, the beam reflected from the second active mirror 30 will intersect with the first active mirror 28 due to the large positive rotation angle of the first mirror 28. On the other hand, if the distance between the two mirrors 28 and 30 is increased, the second mirror 30 must be made larger to accept the incoming light for the large negative rotation angle of the first mirror 28. This is the second two-mirror design (Fig. 28). The same range of motion as the three-mirror design is achieved at the expense of a 50% increase in diameter (the second mirror 30 has a circumscribed diameter of 6 mm). In the left image, the first active mirror 28 is rotated +10° and the second active mirror 30 is at a neutral 0° angle. In the right image, the first active mirror 28 is rotated -10° and the second active mirror 30 is rotated +8°.

[0061] Thus, a three-mirror galvanometer (Figure 26) achieves a larger range of motion than a two-mirror design of the same size (Figure 27), and a two-mirror design (Figure 28) would require a 50% larger diameter to achieve the same range of motion as a three-mirror design. The range of motion is determined primarily by the ability of the mirrors to fully capture and reflect the incident light, but is limited by the need to avoid collisions between the mirrors and between the reflected laser and the previous mirror in the light path. These sample configurations demonstrate the limits of the range of motion where these collisions are likely to occur.

[0062] A fixed beam diameter of 1 mm was assumed throughout this analysis. This is somewhat larger than the low power pointing laser used to validate the device, but is a reasonable upper limit for a collimated high power beam. For simplicity, the neutral position of each mirror was chosen to be at a 45° angle of incidence with the input beam, so that slight deviations from 45° may result in slightly different results but would not change the structure of the design tradeoffs. We also assumed that a symmetric range of motion is desirable. Again, if this is not the case, the resulting design may vary slightly, but it does not have to change the nature of the design space. Finally, we emphasize that we are considering the case where the output beam is parallel to the input fiber (forward looking). If we wanted the output beam to be perpendicular to the input fiber (side looking), there would be no reason to use a three mirror design and a two mirror design would be perfectly acceptable in terms of compactness and range of motion. However, most energy delivery tools used in surgery are forward looking, so we chose to use this configuration for our example device, although other examples of devices could easily use a side looking device.

[0063] With these overall insights in hand, the detailed design and fabrication of the device is undertaken. The fabrication uses a combination of off-the-shelf and custom-made parts, primarily fabricated by laser micromachining (using an Oxford Laser E series with a Coherent Avia 355-7 laser and a Canon galvanometer). The kinematic structure of the three-mirror galvanometer piezoelectric bending actuator motion transmission assembly is shown in Figures 29 and 30, which includes bending actuators 18 and 22, transmission linkage 38, and mirrors 28 and 30. This assembly converts the quasi-linear (parabolic) input motion into rotational motion of the mirrors.

[0064] The components of the three-mirror galvanometer prior to assembly are shown in FIG. 31 (in order of assembly, first row, left to right, then second row, left to right). The components shown include a retaining clip 88, a fixed mirror 42 assembly, a second active mirror (y-axis) 30 assembly, a first active mirror (x-axis) 28 assembly, a focusing lens 34 assembly, a piezoelectric actuator 18 and 22 assembly, a collimating lens 32 assembly, and a support superstructure 90. The retaining clip, mirrors 42, 28, 30, lenses 34, 32, and actuators 18, 22 are each mounted to a disk platform 92 having an orifice through which the platform 92 is slidably mounted to rods 94 of the support superstructure 90, thereby providing a removable modular structure. These components may be formed by cutting with a UV laser. The active mirror 28, 30 assemblies and the piezoelectric actuator 18, 22 assemblies may include precision lamination. Sputter deposition can be used to form the mirror assemblies 28, 30, 42. Lenses 32, 34 can be off-the-shelf components. Finally, diamond grinding can be used to shape the focusing lens 34.

[0065] Specific details of the component design, manufacture, and function are as follows:

[0066] Steel Rod Superstructure 90: This component consists of two 500μm and one 300μm diameter stainless steel rods 94 (Misumi, USA) on which the remaining components are assembled. The rods 94 are aligned perpendicular to the FR4 disk 92 using an alignment jig. A spring steel preload spring is attached to the disk 92 to compress and hold the assembled components in place. All components are laser micromachined.

[0067] Ferrule fiber and collimating lens 32: A commercially available ferrule-terminated optical fiber (SMPF0106-FC, Thor Labs) was assembled with a gradient index collimator 32 (GRIN2306A, Thor Labs) and mounted on an FR4 support disk 92.

[0068] Piezoelectric bending actuators 18, 22: Actuators 18 and 22 were fabricated to size using processes and materials described in NT Jafferis, MJ Smith, RJ Wood, "Design and manufacturing rules for maximizing the performance of polycrystalline piezoelectric bending actuators", Smart Materials and Structures, Vol. 24, No. 6, p. 065023 (2015). The actuator dimensions were chosen to fit the available space adjacent to the optics: active length 7 mm, tip length 1.8 mm, bridge length 0.5 mm, base width 1.4 mm, and tip width 0.4 mm.

[0069] The actuators were driven in a unipolar configuration biased with a fixed bias voltage, so that each was controlled by a single time-varying input signal ranging from zero to the bias voltage. A fixed bias voltage of 200 V was chosen to achieve a significant output displacement while ensuring that the tensile strain of the piezoelectric ceramic was well below its failure limit. Under these driving conditions, the actuator achieved a free displacement of ±200 μm and had a first resonant frequency of 2.6 kHz.

[0070] Focusing lens 34: The focusing lens 34 was obtained off-the-shelf (#89-003, Edmund Optics) and ground down to size using an alignment jig and diamond cut-off wheel. Laser pre-etched registration marks on the lens 34 allow for alignment of the optical center after grinding.

[0071] Articulating mirrors 28, 30 and motion transfer sections: These are complex assemblies of rigid and non-rigid parts fabricated using lamination techniques. They may include a four-bar crank-slider linkage formed from stainless steel, polyimide, and a thermosetting acrylic adhesive (PYRALUX adhesive from Dupont Inc). The mirrors 28, 30 are placed on the cranks and the sliders each interface with one of the piezoceramic actuators 18 / 22. The x-axis (first) transfer section further includes a linearization linkage to compensate for out-of-plane motion of the bending actuator tips. These are shown diagrammatically in Figures 29, 30. The mirrors 28, 30 are made from sputtered aluminum (Denton Depcale Pro PVD system, Denton Vacuum LLC, Moorestown, NJ, USA) on a 100 μm fused silica substrate and singulated using a UV laser.

[0072] The detailed design of the transmission is based on the actuator characteristics. Similar to state-of-the-art devices, we wanted to achieve ±10° of motion for each mirror (driven by bending the actuator in either direction). To achieve this motion, there are two important design considerations: (1) the transmission ratio of the linkage and (2) the stiffness of the linkage relative to the stiffness of the actuator. Based on experience with sizing similar mechanical parts, we chose a target transmission ratio of 0.1° / μm and a target stiffness equivalent to that of the actuator. For this device, we achieved transmission ratios of 0.13° / μm and 0.12° / μm (due to small manufacturing tolerances) and stiffnesses that were 60% and 90% of the actuator stiffness.

[0073] Note that the stiffness of the transfer section is parallel to the stiffness of the actuator, resulting in a reduced free displacement of the actuator. For the two mirrors fabricated in this way, we achieved a range of motion of -12.5 to 20° and -11.2 to 13.7°, respectively. This asymmetry corresponds to slight assembly misalignment and slightly nonlinear transfer kinematics. The neutral (zero) mirror angle and actuator position corresponds to a configuration in which the output beam is aligned along the longitudinal axis of the device.

[0074] Fixed Mirror 42: This aluminum sputtered fused silica mirror 42 is fixed at 45° to the incident beam using two alignment blocks and interfaces with an FR4 support disk 92.

[0075] Retaining Clip 88: This spring steel part fits into a groove cut into a stainless steel rod 94 in the superstructure 90. It works in conjunction with a preload spring located in the superstructure base to axially restrain the assembly.

[0076] Spacer Tubes and Disks: These are laser micromachined components to ensure proper spacing and alignment between components. Their length (or thickness) is the critical dimension.

[0077] We began to characterize the end-effector position control by measuring its open-loop repeatability, an important indicator of the fundamental limitations of the physics of the device to reproduce identical movements. Phenomena such as stiction and plasticity mean that identical inputs do not produce identical outputs. Unidirectional repeatability is a measure of the repeatability of approaching the measurement points from only one direction. The maximum 2σ typical distance of the sampled points is 200 μm, meaning that we can be 95% confident that a series of identical movements will fall within a variance radius of 200 μm relative to the mean trajectory.

[0078] The presence of hysteresis complicates position control. Hysteresis is a bidirectional effect that mainly arises from the reorientation of domains in the piezoceramic actuator, meaning that the laser position depends on the time history of the input. This dependency is clearly undesirable, as it complicates control and makes the use of the device unintuitive. To minimize this hysteresis effect, a feed-forward compensation scheme was introduced. To validate this approach, star trajectories were commanded for inputs without and with compensation. While the raw input clearly shows the effects of path dependence, the compensated input shows significantly improved tracking. This is essentially a measure of bidirectional repeatability. Quantitatively, the maximum 2σ typical distance around the set point is 2.14 mm without compensation and 0.72 mm with compensation, which represents a reasonable improvement of the feed-forward compensation. Further improvements can be achieved with feedback control.

[0079] Due to the low dimensionality of the workspace and input space and the lack of sensor information, we chose to control the device using a model-free direct mapping between the actuator input and the laser spot position, cascaded with feed-forward correction for hysteresis. Cubic and quadratic polynomial surfaces were fitted to the open-loop repeatability measurement data for the first and second mirrors, respectively. These fits were centered at 73V and 93V, respectively, which correspond to the neutral angles of the mirrors.

[0080] The system can be dynamically controlled and characterized. The bandwidth of the system is limited by the mirror resonances at high frequencies. As seen in the Bode plots shown in Figure 32 (plot of frequency response of the first active mirror to a low voltage white noise input) and Figure 33 (plot of frequency response of the second active mirror), the primary resonant frequencies of the two mirrors are 1.8 kHz and 1.9 kHz. In addition, the first mirror has a low frequency mode at 1.2 kHz (likely due to torsion and other off-axis modes). To avoid the occurrence of these modes, a finite jerk motion profiling method (also known as sigmoidal or S-profiling) is used.

[0081] The system shows only minor deviations from the static trajectory 26 at high speeds, as can be seen in Figures 34 and 35. There is only a 5% deviation between the trajectories followed at low (7.8 mm / s, solid plot in Figure 35) and high (3,900 mm / s, dashed plot in Figure 35) speeds. The two-axis control also allows the system to trace complex planar trajectories. The wide bandwidth of the system can also be utilized to generate multi-modal profiles. These are trajectories where a high frequency input is superimposed on a low frequency input, allowing the user to vary the effective area of ​​energy application on the fly, which is particularly useful in situations where a large area needs to be controllably covered, such as large area hemostasis.

[0082] The laser steering end effector's low profile and small mass (e.g., 700 mg) allows for easy interfacing with existing surgical instruments. To demonstrate this, we attached it to the end of a colonoscope (Olympus CF-100L) and performed a simulated polyp resection task on a benchtop surgical simulator. We demonstrate both remote control using a standard input device (Phantom Omni) and high-speed robotic control of the laser along a registered incision trajectory.

[0083] This work points the way to new ways of controlling energy delivery in minimally invasive surgery. It can simultaneously address three important challenges in surgical techniques: (1) allowing the surgeon to have greater control over energy delivery to soft tissues, (2) improving the maneuverability and dexterity of the surgical tools, and (3) reducing the physical burden on both the surgeon and the subject. This contribution allows the surgeon to control the laser speed as it interacts with the tissue, allowing a wider tuning and optimization of the quality of the laser-tissue interaction than with existing statically used tools. Using a wrist-type joint, the surgeon can access previously inaccessible lesions. Our design, fabrication, and modular assembly approach are additional contributions that enable the creation of this device, but are also adaptable to other complex microrobotic systems and medical devices.

[0084] To achieve precision along the repeatability of the device, sensory feedback can be incorporated. A simple approach is to embed strain gauge sensors within the piezoelectric bending actuator to estimate the actuator position and current sensing to estimate the actuator velocity. The mirror position can then be calculated from the transfer kinematics and the laser position estimated from a specular reflection model. Direct measurement of the mirror position allows a more accurate estimation of the laser position, but the path to a suitable fine sensing method is not as straightforward as sensing the actuator movement. Also, visual feedback can be used to provide a high quality estimate, albeit at a lower sample rate than electromechanical sensors. In practice, sensor fusion, fusing these various pieces of information, seems to be the best approach.

[0085] Furthermore, by incorporating appropriate high-power fibers, lenses, and mirrors, the device can be used for surgical lasers. The choice of components depends on the wavelength and power of the laser used. For example, when using a CO2 surgical laser, gold-sputtered aluminum mirrors and zinc selenide lenses provide suitable reflectivity and transmission, respectively. Particular attention is paid to the "laser-induced damage threshold," a measure of the laser power that an optical component can receive before it degrades.

[0086] Regardless of the laser modality used, the device can be advantageously encapsulated to be robust against fluids and debris in the surgical environment and sterilizable. Because the tip of the laser fiber can become damaged over extended use, it can be advantageous to incorporate a method to detach the laser fiber from the device. This detachment capability allows for the laser fiber to be cleaned and cleaved separately, significantly extending the lifespan of the laser fiber.

[0087] Because the laser position is controlled electronically rather than cable actuated, energy control can be decoupled from the overall motion of the surgical instrument on which the laser is located. This independence is particularly important in flexible endoscopy, which often requires tedious manual procedures such as device handoff, endoscope placement, multiple hand movements to various parts of the instrument, and manipulation of the end effector by another user. It is therefore easy to imagine that a remote control column such as a joystick, which is free of position dependency due to the spatial constraints of a cable and can be ergonomically mounted anywhere on the endoscope or on a second operator remote from the endoscope, could improve the efficient use of time in the operating room that is used for patient care rather than device operation.

[0088] Our laser steering approach also enables new approaches for endoscopic visualization and visual biopsy. Optical coherence tomography and confocal endoscopy exploit laser / tissue interactions to visualize subsurface structures, allowing scanning to view large areas of tissue at once. Optical steering can also be used to extend the effective field of view of standard white-light imaging tools by stitching together a series of images acquired in rapid scans. The scanning systems and modular device assembly approach described herein can be adapted to fabricate millimeter-sized versions of those systems. Even smaller versions of these systems are built using laminate fabrication techniques that use electrostatic and electrothermal actuators to excite resonant scanning elements. Our approach has the advantage of being simple in construction and capable of achieving a large quasi-static range of motion.

[0089] The technique also holds promise for applications in other microrobotic systems, especially small aircraft and satellites where size and weight are at a premium. The technology could enable the production of miniature Light Detection and Ranging (LIDAR) sensors used for mapping and navigation, and laser scanners for detecting large areas of air pollution.

[0090] Additional examples consistent with this teaching are provided in the following numbered items:

[0091] 1. A compact laser steering end effector comprising: a frame having a proximal end and a distal end, the frame having a maximum dimension in a plane perpendicular to the longitudinal axis of 13 mm or less; at least two mirrors mounted proximate a distal end of the frame, the mirrors including a first active mirror and a second active mirror; a first actuator attached to the frame and configured to change a tilt of the first active mirror relative to the frame; a second actuator attached to the frame and configured to change a tilt of the second active mirror relative to the frame; A path is provided through the frame to deliver a laser beam to the mirrors, the mirrors being positioned and configurable via the actuator to reflect the laser beam off each mirror toward an external target. 2. The compact laser steering end effector of item 1, further comprising a third mirror positioned and configured to reflect the laser beam together with the first and second active mirrors. 3. The compact laser steering end effector of item 2, wherein the third mirror is fixedly mounted. 4. The compact laser steering end effector described in items 1-3, wherein the first and second actuators are cantilevers. 5. The compact laser steering end effector of item 4, wherein the cantilever is coupled to a mirror via a passive linkage. 6. The miniature laser steering end effector of item 4 or 5, wherein the cantilever is a bimorph piezoelectric cantilever. 7. A miniature laser steering end effector as described in items 1-6, further comprising a surgical laser positioned to direct a laser beam through the miniature laser steering end effector and onto a mirror for steering via reflection from the mirror. 8. The compact laser steering end effector of item 7, further comprising a navigating laser positioned to direct a laser beam through the compact laser steering end effector to a mirror for steering via reflection from the mirror. 8.1 The compact laser steering end effector described in item 1, wherein the frame comprises a plurality of rods and a plurality of platforms attached to the rods, and the components of the compact laser steering end effector are attached to the platforms. 9. A robot laser steering method comprising: generating a laser beam; directing the laser beam into a proximal end of an end effector and directing the laser beam toward a region proximate a distal end of the end effector; reflecting a laser beam off at least two active mirrors at a region proximate a distal end of the end effector; using actuators to change the tilt orientation of the at least two active mirrors to move the laser beam across a target; The method includes: 10. The method of claim 9, further comprising displacing the laser beam with a third mirror in combination with the at least two active mirrors. 11. The method of claim 10, wherein the third mirror is fixedly mounted. 12. The method according to any one of items 9 to 11, wherein the actuator is a cantilever. 13. The method of claim 12, wherein bending the cantilever displaces a passive linkage coupled to the mirror, thereby changing the tilt of the mirror. 14. The method according to any one of items 9 to 13, wherein the target is a living organism. 15. The method according to item 14, wherein the organism is a human. 16. The method according to item 15, further comprising the step of performing in situ resection of benign or cancerous lesions of the pharynx and larynx, or laser-assisted cardiac ablation, laser-assisted surgery of the gastrointestinal tract, laser-assisted abdominal surgery, or laser-assisted transnasal skull base surgery within the human body via the displacement of the laser beam by the mirror.

[0092] In describing embodiments of the invention, specific terminology is used for the sake of clarity. For purposes of description, specific terminology is intended to include technical and functional equivalents that operate in a similar manner to achieve at least a similar result. Furthermore, in some instances where a particular embodiment of the invention includes multiple system elements or method steps, those elements or steps can be replaced with a single element or step. Similarly, a single element or step can be replaced with multiple elements or steps that serve the same purpose. Furthermore, when various characteristics or other value parameters are specified herein for embodiments of the invention, those parameters or values ​​may be adjusted up or down (or increased by 1, 2, 3, 4, 5, 6, 8, 10, 20, 50, 100 times, etc.) unless otherwise specified, or to a rounded approximation thereof, or within a range above or below any of the above mentioned variations for the specified parameter (e.g., if the specified parameter is 100 and the variation is 1 / 100, the parameter's value is in the range of 0.99 to 1.01). Moreover, while the invention has been shown and described with reference to specific embodiments thereof, those skilled in the art will understand that various substitutions and changes in form and details may be made without departing from the scope of the invention. In addition, other aspects, features, and advantages are also within the scope of the present invention, and not all embodiments of the present invention necessarily achieve all advantages or have all of the features described above. Moreover, steps, elements, and features discussed herein with respect to one embodiment can be used in combination with other embodiments as well. The contents of references, including references, journal articles, patents, patent applications, and the like, cited throughout the text are incorporated herein by reference in their entirety for all purposes. And, all suitable combinations of embodiments, features, characterizations, and methods from these references and this disclosure may be included in embodiments of the present invention.Additionally, components and steps identified in the Background section are essential to this disclosure and may be used in combination with, or in place of, components and steps described elsewhere in this disclosure within the scope of the present invention. In a method claim (or where a method is recited elsewhere), where steps are recited in a particular order (with or without order letters added for ease of reference), the steps are not to be construed as limited chronologically to those orders unless otherwise stated or implied by the term or phrase.

Claims

1. 1. A compact laser steering end effector, comprising: a frame having a proximal end and a distal end, the frame having a maximum dimension in a plane perpendicular to the longitudinal axis of 13 mm or less; at least two mirrors mounted proximate a distal end of the frame, the mirrors including a first active mirror and a second active mirror; a first actuator attached to the frame and configured to change a tilt of the first active mirror relative to the frame; a second actuator attached to the frame and configured to change a tilt of the second active mirror relative to the frame; the miniature laser steering end effector extends from or is attached to a microrobotic tool for energy delivery and is configured to receive a laser beam input from an optical fiber extending through the microrobotic tool; A path is provided through the frame to deliver the laser beam from the optical fiber to the mirrors, the mirrors being positioned and configurable via the actuator to reflect the laser beam off each mirror toward an external target.

2. The compact laser steering end effector of claim 1 , further comprising a third mirror positioned and configured to reflect the laser beam in conjunction with the first and second active mirrors.

3. The compact laser steering end effector of claim 2 , wherein the third mirror is fixedly mounted.

4. The compact laser steering end effector of claim 1 , wherein the first and second actuators are cantilevers.

5. The compact laser steering end effector of claim 4 , wherein the cantilever is coupled to the mirror via a passive linkage configured to linearize the out-of-plane motion of the cantilever.

6. The miniature laser steering end effector of claim 4 , wherein the cantilever is a bimorph piezoelectric cantilever.

7. 10. The miniature laser steering end effector of claim 1, further comprising a surgical laser positioned to direct a laser beam through the miniature laser steering end effector and onto a mirror for steering via reflection from the mirror.

8. 8. The compact laser steering end effector of claim 7, further comprising a navigating laser positioned to direct a laser beam through the compact laser steering end effector to a mirror for steering via reflection from the mirror.

9. The miniature laser steering end effector of claim 7, wherein the microrobotic tool is a minimally invasive surgical tool extending from or attached to the miniature laser steering end effector.

10. The compact laser steering end effector of claim 1 , wherein the frame comprises a plurality of rods and a plurality of platforms attached to the rods, the platforms having components of the compact laser steering end effector mounted thereon.

11. 1. A robotic laser steering method comprising: generating a laser beam; directing the laser beam through an optical fiber extending through a microrobotic tool into a proximal end of an end effector and directing the laser beam toward a region proximal to a distal end of the end effector; reflecting a laser beam off at least two active mirrors at a region proximate a distal end of the end effector; using actuators to change the tilt orientation of the at least two active mirrors to move the laser beam across a target; Including, The method is not carried out in any of a method of surgery on a human body, a method of treatment on a human body, and a method of diagnosis on a human body.

12. The method of claim 11 , further comprising displacing the laser beam with a third mirror in combination with the at least two active mirrors.

13. The method of claim 12 , wherein the third mirror is fixedly mounted.

14. The method of claim 11 , wherein the actuator is a cantilever.

15. The method of claim 14 , wherein bending the cantilever displaces a passive linkage coupled to the mirror, thereby changing the tilt of the mirror.

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