Laser Eye Surgery Robot

Transcription

1 Laser Eye Surgery Robot Jonathan Hipps, Alejandro Osorio, Gianfranco Pisani, Sebastian Rojas, Melissa Morris, Sabri Tosunoglu Florida International University Department of Material and Mechanical Engineering West Flagler Street Miami, Florida, USA ABSTRACT This paper proposes the design of a new robotic system that is more compact and provides easier operation of the system than the standard laser eye surgery equipment used in the optical correction field. This system showcases the kinematics that went into the overall look and design of the presented robot as well as the proposed parts, motors and materials that would eventually make up the general design of the laser eye surgery robot in this paper. Keywords Eye Surgery, Robots Design, Robots Kinematics Figure 1. Robotic Laser Eye Surgical Equipment. 1. INTRODUCTION The objective of this assignment was to create a new system design for a robotic product used in the industry. For our group study, we opted to create a new design feature for the robotic laser eye surgery equipment used in the medical optical field. While laser eye surgery is no new feat, the system can prove to be cumbersome and somewhat of a challenge to operate. In the field of eye correction surgery, there can be little to no margin of error when it comes to corrective surgery. In this project, our group has generated a new design feature to the laser eye equipment so that it is easier to operate and to set up for the patient. The final design of our optical surgical equipment is shown in Figure 1. The overall design involves the use of a telescoping arm to position the laser beam near the patient s eye. The laser is located within the table, and is directed to the end of the arm via semi-adjustable mirrors. A fully-actuated mirror that is able to precisely direct the laser beam to the desired locations is located at the end-effector.. 2. CALCULATIONS AND KINEMATICS In order to calculate the kinematics of this robot, a special approach has to be made as the laser final location is influenced by optics laws, the eye curvature and the semi-infinite extension of laser light. When a ray of light strikes a plane mirror, the light ray reflects off the mirror. Reflection involves a change in direction of the light ray. The convention used to express the direction of a light ray is to indicate the angle which the light ray makes with a normal line drawn to the surface of the mirror. The angle of incidence is the angle between this normal line and the incident ray; the angle of reflection is the angle between this normal line and the reflected ray. According to the law of reflection, the angle of incidence equals the angle of reflection. These concepts are illustrated in the Figure 2. In order to satisfy this law, the mirror surface has to be almost perfectly flat and polished Florida Conference on Recent Advances in Robotics 1 Melbourne, Florida, May 14-15, 2015

2 where is the distance of the laser to the eye surface described by the parameterization curves, is the extension of telescope system and is the third mirror inclination angle. The way the laser can reach the eye surface in different ways is shown in Figure 5. Figure 2. Law of Reflection Second, the parameterization of the eye is made, so the kinematic simulation can be accurately done, it is parameterized assuming the eye as a sphere of dimensions shown in Figure 3. Figure 5. Movement of Laser for Two Typical Surgical Movements Figure 3. Typical Eye Dimensions The parametric equations for spherical curves and surfaces are: sin cos sin sin cos Where is the eye radius, and are the polar angles as shown in Figure 4 and taken from Figure 3. With these equations the inverse kinematics can also be calculated for a given position in the eye as: 2, With all previous equations a MatLab function library was created in order to simulate the movement of the laser. The code and simulation can be seen on reference. The dimensions to be used in the kinematics when the arm is fully expanded are shown in Figure 6. Figure 4. Spherical Polar Coordinates Now, from the analysis of the dimensions the forward kinematics can be established as tan Figure 6. Physical Dimensions of the Arm 2015 Florida Conference on Recent Advances in Robotics 2 Melbourne, Florida, May 14-15, 2015

3 3. ACTUATORS AND PISTONS FOR THE SURGICAL ROBOT In this design project, there are only a few moving parts to this equipment. The largest moving part of the robot is the telescoping arm as shown in figure 1. For this robot arm, a piston was needed that could not only support the weight of the telescoping arm of the robot at full length, but one that will also move the arm gently due to the dexterity involved with laser eye surgery. For this report, we chose to use the Concentric LACT10P-12V-20 Linear Actuator. This actuator has a 20:1 gearbox ratio for gentle movements while it has a maximum speed of 0.5 in/s (1.3 cm/s). It is also capable of handling a dynamic load of 110 lbs. (50 kg) making it just as capable of handling the telescoping arm at its fullest extended length. Below are two images of the actual piston with its specifications and the SolidWorks design of the piston for the design assembly of the robot. The actuator characteristics are: Gear ratio:20:1 Free-run current at 12V: 500 ma Stall current at 12V: 10 A Linear speed at 12V: 0.5 in/s Linear force at 12V: 110 lb Maximum duty cycle: 25% small spaces of our robot arm for the mirrors themselves. This motor is chiefly designed and built by Maxon Motors, Inc. one of the leading manufacturers of high precision motors for medical fields. This motor is most notable for being presently used in the da Vinci Robotic Surgical System. Below is an image of the motor itself including the general specifications of the motor: Figure 4. RC 25 Motor With general specifications: Bearing type: Ball bearings Max. speed: rpm Axial play: mm Nominal voltage: 18 V No load speed: rpm Nominal speed: 8850 rpm Stall torque: 220 mnm Weight: 130 g Figure 7. Concentric LACT10P-12V-20 Linear Actuator 4. MATERIALS AND PARTS FOR THE SURGICAL ROBOT In most laser machines, one or several mirrors are used to forward the laser beam from the cavity to the working head. Usually, each mirror deflects the laser beam at an angle of 90, corresponding to an angle of incidence of 45. At these mirrors, reflectance should be as high as possible in order to minimize loss of laser power. In addition, phase shift between the s- and p-polarized components of the reflected beam should be as low as possible in order to avoid disturbing the polarization of the laser beam. Mirrors with such properties are called zero-phase mirrors. This type of mirrors will be used to guide the laser beam from its source to the end position required by the practitioner with as minimum as possible power decay from the reflection on the surface. Figure 8. SolidWorks Design of the Linear Actuator The movement of the mirrors themselves had to also be addressed, as they required absolute precise movement during surgery of the eyes. For this robot design, we opted to us the RE 25 motors. These motors are small enough to be able to fit in the 2015 Florida Conference on Recent Advances in Robotics 3 Melbourne, Florida, May 14-15, 2015

4 used; the base must be manufactured with high precision due to the alignment of the beam. Figure 9. CO2 Zero Phase Mirrors CO2 mirrors will have different shapes depending on the position on the assembly, square shaped mirrors will be at the end on the telescopic actuator, and circular mirrors will be at the base, allowing the correct guidance of the beam with the best possible precision. Square and circular shaped mirrors are shown below; these two parts are the ones used in the assembly of the robot. Figure 12. Assembly Base For the telescopic actuator, the creation of it requires different pieces in order to serve its purpose. Initially two rings will attach the telescopic assembly to the base, and then each circular ring will attach to the next one until all three of them are aligned. Inside the rings the laser beam will go through them, using the mirrors as a guide. Again the precision required at this level is very high; a slight variation on the measurements and the beam could be off target. Figure 10. Square Shaped Mirrors Figure 13. Telescopic Attachment Figure 11. Circular Shaped Mirror Figure 14 shows one individual ring. All the rings are similar in shape but with different measurements. Since each one of the rings, in order to contract, has to be larger in radius or smaller in order to be able to create the telescopic motion needed for the arm. The base of the assembly will be manufactured with aluminum as shown in Figure 12. It can be manufactured as two parts or as a single billet one, independently of the manufacturing process 2015 Florida Conference on Recent Advances in Robotics 4 Melbourne, Florida, May 14-15, 2015

5 been motorized. This all contributes to a more fluid measuring process and a more accurate end result of smooth operation compact & modern design, 8.5 inch LCD touch screen panel as seen in Figure 16. Figure 14. First and Second Ring Figure 15 demonstrates how all rings and attachment mated together to create the complete arm. This arm coupled with the linear actuator will account for the linear motion of the arm. Figure 17. Pascal Laser Photocoagulador As you see in Figure 17, the laser can produce different laser shapes depending on the eye disease itself. This laser is greatly recommended for our project because it provides treatment closer to the fovea without fear of causing retinal damage or vision loss. It can also be used for retinal and glaucoma disorder. 5. DESIGN AND ASSEMBLY OF THE ROBOTIC LASER EYE SURGERY EQUIPMENT The following section will cover the complete assembly: Figure 18 shows a section view of the laser eye surgery robot for our design. This view shows the interior of the assembly and how the laser is guided with the mirrors Figure 15. Telescopic Attachments Assembled Figure 18. Section View Figure 16. Computerized Tonometer CT-800 Topcon's ability to engineer a weight reduction of approximately 22 % has contributed to a smoother operation of the unit when using the X-Y control lever. The up/down movement has also Initially the laser beam comes from a source under the table; this allows the laser to be safely removed without the laser equipment causing any injury to the patient. Therefore, it creates a less aggressive equipment and more friendly to the eyes of the patient in term of visual aspects. Also removing the laser source from the table makes the patient more calm with a more welcoming place. This was one of the major goals for the creation of this robot; 2015 Florida Conference on Recent Advances in Robotics 5 Melbourne, Florida, May 14-15, 2015

6 create something more appealing and approachable than any other predecessor, giving the patient a more relaxed procedure, thus making the surgery a relaxed experience. After the beam has being released from the source, it starts by hitting the first and only circular mirror, whose position is fixed. The angle of incidence for this mirror is 45 degrees with respect to the x-axis which in term results in a 90 degrees difference between the incoming and outgoing beam, creating the first change in direction of the beam. Then the beam comes to the second mirror, which is a square mirror also with a fixed position of 68 degrees with respect to the x-axis, resulting in a change of direction following mirror reflection law, to reach the third and last mirror. The third mirror is the most important one, since this will be the one responsible for the laser s direction and end point position. This mirror is not fixed; it can roll and pitch to be able to reach all the points on the circular surface of the eye. Also it is important to say that the first and second mirrors are fixed, but they can be moved if the assembly is modified. They are not moved automatically since that would introduce errors by adding degrees of freedom, and that is simply not desired, therefore these two mirror are fixed manually and can be finetuned if it is required by the practitioner. Figure 19 and 20 shows the complete assembly from different orientations. This helps to visualize the complete assembly and how it completes its assigned tasks. Figure 20. Top Angle View 6. CONCLUSION The laser eye surgery robot underwent several design changes before the final design shown was agreed upon. While the eye surgery robot was initially intended to be more compact in order to allow for ease of transportation to other parts of the world, this design was established to be easier to operate without so many moving parts to work with. In conclusion, this design our group feels will allow optical doctors the austerity of treating the patient without the overwhelming task of getting the surgical equipment ready for the patient. 7. ACKNOWLEDGMENTS One of the authors, Melissa Morris, would like to thank the DOD/Army Research Office for providing support under grant no. ARO Grant No. W911NF to perform this research. Their support is very much appreciated. 8. REFERENCES Figure 19. Isometric View [1] M. Nowakowski, "Measurements of the field-dependent monochromatic aberrations of the human eye.," National University of Ireland Galway, [Online]. Available: [Accessed ]. [2] S. Tosunoglu and D. Tesar, Robotics and Automation, University of Texas at Austin, [3] Department of Mathematics, "Parameterized Surfaces," Harvey Mudd College, [Online]. Available: Geometry/Geometry_of_surfaces/Parameterized_Surfaces.htm l. [Accessed ] Florida Conference on Recent Advances in Robotics 6 Melbourne, Florida, May 14-15, 2015

7 [4] J. J. Craig, Introduction to Robotics. Mechanics and Control, Pearson Education, [5] Michael J. Newton, MD, "The Promise of Telemedicine", Department of Ophthalmology, Mount Sinai Hospital, New York, New York, 11 February 2014 [6] Ron Hendrix, " Robotically Assisted Eye Surgery: A Haptic Master Console", Eindhoven: Technische Universiteit Eindhoven, Proefschrift, Eindhoven University of Technology Library, ISBN: [7] John D. Pitcher¹, Jason T. Wilson², Tsu-ChinTsao¹, Steven D. Schwartz¹, Jean-Pierre Hubschman¹, " Robotic Eye Surgery: Past, Present, and Future", ¹Jules Stein Eye Institute, Department of Ophthalmology, University of California, David Geffen School of Medicine, Los Angeles, USA ²Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, USA, 2012 [8] Puwat Charukamnoetkanok, Kittipong Ekkachai, Narisara Klanarongran, Teesid Leelasawassuk, Prakob Komeswarakul, Pitipong Suramethakul, Oraorn Thonginnetra, Somkiat Asawaphureekorn, Sunisa Sintuwong, Kanokvate Tungpimolrut, Waree Kongprawechon, Pannet Pangputhipong, "Robotic Slit-Lamp for Tele-Ophthalmology", ICROS-SICE International Joint Conference 2009, August 18-21, 2009, Fukuoka International Congress Center, Japan 2015 Florida Conference on Recent Advances in Robotics 7 Melbourne, Florida, May 14-15, 2015