Surgical Robot


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Surgical Robot

  1. 1. Surgical Robot: Endoscopic Retractor/Stabilizer Team Members:Jose Pizano, David Pearson, Jonathan Keeble, Sergio Lares, Chuc Nguyen, and special support from Mike Dragulin Date of Report: 3-17-2003 Revised 6-8-2003 Industrial Advisor: Dr. Mike Savitt M.D. St. Vincent’s Hospital Progress Report For ME492 Page 1 of 14
  2. 2. Contents:Executive Summary: 2Introduction: 2Design Brief: 3Latest Project Planning Document: 3Final Product Design Specification Summary: 4External Search Summary: 6Internal Search Summary: 8Final Design Selection Summary: 9Progress on Detailed design 11Conclusion and recommendations: 14Appendix: 14 Project Proposal Product Design Specifications External Search Internal Search Concept Evaluation Document Page 2 of 14
  3. 3. Executive Summary: The purpose of this project is to develop a combination retractor stabilizer capable ofbeing inserted endoscopically into a patient’s chest to assist in robotic heart surgery. This devicewould help reduce the time spent in surgery by allowing the surgeon to quickly retract the heartand stabilize portions of interest. A single design has been chosen and partially developed. Thefinal goal of this project is to construct a working prototype that can be tested on a live pig.Future plans include a production level design and a new automated design.Introduction: The Da Vinci robot is a system that allows surgeons to perform traditionally invasivesurgeries with minimally invasive techniques. The robot’s appendages are inserted into a patientthrough small holes ranging from 6 to 15mm. The surgeon controls the robot from a nearbyconsole that offers stereoscopic views of the inside of the patient and tactile feed back from therobot’s appendages. The Da Vinci Robot allows surgeons to perform complicated surgerieswhile minimizing damage to the patients. This endoscopic approach minimizes the length ofhospital stays and reduces patient recovery time. At St. Vincent’s hospital, the Da Vinci robot isused to perform valve replacement surgery and coronary bypass surgery on patents with heartdisease. The average hospital stay for these patients is reduced from 10 to 3 days when the robotis used in place of typical open-heart surgery. One drawback to the robotic surgery is that it usually takes twice as long as conventionalsurgery, which increases the risks associated with anesthesia and costs more because it requiresmore time in the operating room. Reducing operating room time helps improve the odds ofpatient survival and reduce hospital costs. Page 3 of 14
  4. 4. Design Brief: The purpose of this project is to design and build a retractor/ stabilizer capable of beingused endoscopically to assist the Da Vinci robot with heart surgery. A retractor allows the heartto be moved or rotated and a stabilizer immobilizes a portion of the heart. There are endoscopicstabilizers available for this operation, but these require the surgeon to use the robotic grippers tobring the heart to the stabilizer. A combination of a retractor and stabilizer would save time byperforming multiple functions and help reduce the risks associated with lengthy procedures.Latest Project Planning Document: In the Winter term of 2003, our team developed several preliminary designs based on thedesign criteria laid out by Dr. Savitt. One of these designs was selected after a long eliminationprocess. The chosen design has been further developed with computer modeling and FEAanalysis. The plans for the Spring 2003 term include final development of the chosen design usingcomputer aided stress analysis. A prototype will be built and tested for range of motion,strength, and ease of use in a mock-operating room situation. If the prototype appears to workwell, it may be tested on a live pig to further prove its effectiveness. Future plans for the device will include full scale production and distribution to help aidin cardiac surgery. This design may also be electronically automated to allow it to be integratedinto a robotic surgery system. Page 4 of 14
  5. 5. Final Product Design Specification Summary Customers:When a production version of the device is made, other surgeons along with hospitals, nursesand technicians will become the customers. Product Design Specifications:Space constraints: The device will need to be capable of being deployed through a guide tube which is to beinserted in a patient’s chest. The guide tubes available have an inner diameter of 6, 10, and12mm.Operation: The retractor/stabilizer must be capable of gripping and rotating a human heart 180 to270° in either direction about the heart’s connecting vessels. Once rotated the heart’s surfacemust be held in place with a rotational deflection of less than 1mm. After being rotated, thedevice will need to be able to immobilize a small area of the heart ranging between 1 to 3cm2 andresist any deflections of more than one millimeter in any direction.User Interface: Our prototype is being designed to function as a stand-alone device, capable of beingused in conjunction with the Da Vinci robotic surgery system. It should be able to be used byone person in the operating room with independent control of motion, tightening, and suction ofeach component of the device. Page 5 of 14
  6. 6. Maintenance: If the design is to be a multiple use item, all components will need to be replaceable and easily cleaned. A multiple use item is intended to last for 500 surgeries, however any wear on the tool should be visually evident to help reduce the risk of bringing a worn instrument into the operating room. Materials: The device should be easy to sterilize. Rigid components should be able to survive in a steam autoclave with no damage or corrosion, flexible components should be able to be gas sterilized or be disposable. All materials will need to be certified by the FDA for use in surgery. Cost: A disposable single use device should cost between $100 and $300. A device designed for repeated use may cost between $3000 and $5000 for manufacture. Design Engineering Specifications:Item Metric Importance (10 high, 1 low)Grip force / resistance to movement Force will vary, deflection must always be less than 1mm in all 10 directions.Rotational range of each set of 180 to 270 degrees in both directions 10appendagesMovement of stabilizing/retracting Must conform to the surface of an adult heart and be independently 10appendages controllable and deployable.Width of guide tube Can be 6, 10 or 12mm wide, circular profile 8User Interface Must be effective, comfortable, non-obstructive to robot movement 9Sterilization Able to be sterilized, allows for required strengths 10Maintenance Ease of cleaning, replaceable components 6Cost $100 to $300 disposable option or $3000 to $5000 long term use 2 option Page 6 of 14
  7. 7. External Search Summary: The purpose of the surgical robot project is to combine a cardiac retractor and stabilizerinto one device. Currently there is no product on the market that combines a stabilizer andretractor into a single device. There are many devices on the market that aid in open heartsurgery but only few that aid the Da Vinci surgical robot. When the surgical robot is used toperform heart surgery the recovery time is cut from about ten to three days. The types of devicesmost commonly used for open heart surgery are a retractor and stabilizer, see figure 1 below.However, the retractors and stabilizers are disposable and expensive.Fig 1: Picture of a stabilizer and retractor.Search on Materials As a general rule all the materials that are used in heart surgery need to be biocompatible.The same rule is applied to this project, for example; the considered materials must be easy tosterilize, clean, and be biocompatible. Some of the considered materials for the project (i.e.senior project) are stainless steel (303 & 304), Stylistic™, PVC (plastic), and titanium. All ofthe mentioned materials have one thing in common; they are biocompatible and are used in themedical field. Page 7 of 14
  8. 8. A newer type of technology that is used in heart surgery is the Symmetry™. This deviceis simple yet claimed to be effective. The Symmetry™ uses three other tools: 1) aortic, 2)delivery system, and the 3) aortic connector. This device has the appearance of a screwdriver, seefigure 2. Fig 2: Picture of the Delivery SystemOpen heart surgery in looking to be a thing of the past. Today there are several different types ofrobots including: Da Vinci™, ZEUS™ Surgical System, and the AESOP™ Robotic System. Eventhough these robots exist, they are still in their infancy. Also many of these robots are difficult touse and using them is more expensive than open-heart surgery. Although surgical robots are relatively new, they have many obvious advantages, they aregreat deal more precise and do not tremble. The incisions made will continue to get smaller andopen heat surgery will be less common. Many new exciting materials are introduced every yearsuch as memory alloys and Silastic™, and surgical tools are getting smaller. The materials andtechnology discussed in the external search were considered while coming up with ideas forprototype designs related to our project. We looked at proven designs of retractors andstabilizers to help determine whether our designs would work. The materials that will be used inour final prototype will need to have the qualities discussed in this search document. Page 8 of 14
  9. 9. Internal Search Summary: The group generated several concepts for designs that could fulfill the designspecifications. The two designs considered to have the most potential are listed below. The first idea, called the Duck Foot, consists of a single suction cup retractor and anarticulated stabilizer. The Suction cup would unfold after passing through the guide tube andencompass the apex of the heart. Once it was in position, suction would be applied and thedevice would grip. Steel ribbon reinforcement within the suctioning device would ensure that itwould not simply tear apart once the device turns to rotate the heart.In order for this design to stabilize the heart, a separate stabilizer is used. This stabilizer issimilar to the Octopus™ device sold by MedTronics, redesigned to fold into a compact packagefor deployment through a tube. Two suction cupped arms roughly two inches in length attachedtogether by a hinge similar to that in the center of a pair of scissors. The main control rod forgross movement of the stabilizer attaches to this central hinge. Initially, the arms fold togetherinto a narrow package that fit down the tube. Once they were over their final position, tensorwires attached to the rear of each arm pull backwards, unfolding the arms into a shape similar tothe Octopus™. Suction applied through the arms would stop that area of the heart from movingwith the heartbeat. The second design of importance is the Undertaker. The Undertaker is a radiallysymmetric mechanical gripper. The design features three fingers individually positionable withthe controls. Once a finger is in the proper position, the control can lock the finger into place. Asimple vacuum powered suction cup at the base of the end effector holds the heart in a requiredlocation. Page 9 of 14
  10. 10. The fingers have two degrees of freedom. The fingers rotate about the base, and bend at aswivel joint halfway along the finger. The rotation is powered through simple manual rotation ofthe control, while the bending action is motivated by a combination of tensors wire connectingthe joints to the controls, along with torsion springs working to extend the joints. The Penetrada is a similar design to the Undertaker that used a wire lasso for grippingstrength. The Chalupa used a net to enfold and grip the heart. The ET hand was an asymmetricalthree fingered gripper with suction cups at the tips of the fingers. All three of these are detailedin the Internal Search.Final Design Selection Summary:The final design for the prototype was decided upon using several criteria. The most importantcriteria were functionality, ease of deployment, and simplicity(see table E1 for a description ofthe selection criteria). The full selection process is outlined in the Final Selection Appendix. PDS Criteria Metric Importance (5 high, 1 low) Functionality The ability of the equipment to operate as expected 5 during actual surgery conditions in the hospital without breaking Ease of Deployment It has to deploy within 3 to 4 inches(end tube from 5 the bottom heart apex) Simplicity It has to be as simple as possible, because of space 5 constrains Reliability Lasts 500 surgeries 4 Maintenance Ease of cleaning, replaceable components 4 Life Span 3-5 years 4.5 Cost $100 to $300 disposable option or $3000 to $5000 1 long term use optionTable E1: Description of design selection criteria.Of the several designs considered, a few were quickly eliminated. The E.T. Hand was toocomplex, and an effective prototype wouldn’t be able to fit within the space constraints. TheChalupa was incapable of deploying properly. Page 10 of 14
  11. 11. The other three designs received more discussion and consideration. The Penetrada waseventually eliminated because the design was too complex, and it would not deploy reliably. TheDuck Foot was a workable design, but the appendages were too similar to existing patenteddesigns. The concept selected for the final design was the Undertaker. The design is completelymechanical, so the group is fully aware of its capabilities and hindrances. Its individuallypositionable prongs allow it to deploy in a variety of positions and deliver force where it isneeded. Table E2 shows a concept screening matrix used to help eliminate poor designs based onthe opinions of the group members. Our industry contact Dr. Savitt also helped us to select thebest designs based on drawings and prototypes we had built.Concept screening1-5 (5 being the highest score) PDS Criteria Datum E.T Duck Penetrada Undertaker Chalupa Suctioner Hand Foot Functionality 0 2.5 4.5 3.75 3.5 3.0 4.0 Ease of Use/ 0 3.5 3.66 3.25 3.5 3.0 2.0 deployment Cost 0 3.0 3.84 3.25 3.84 3.5 3.0 Reliability 0 3.5 3.5 3.25 3.5 3.0 2.0 Complexity 0 2.5 4 3.84 4.5 3.5 2.5 Life Span 0 3 3.20 3.5 3.33 3.0 3.0 Maintenance 0 3 3.5 3.5 3.84 3.0 3.5 Total 0 21.0 26.2 24.34 26.0 22.0 20.0Table E2: Concept design matrix. Page 11 of 14
  12. 12. Progress on Detailed design Out of the many prototypes and conceptual ideas that were developed during the springand fall term only the top contenders were chosen as the final selection in the development of thefinal senior project. The top two contending conceptual ideas for the final selection are asfollows: Duct foot and the Undertaker(Fig 3). However, the undertaker was chosen as theprimary prototype since it better fulfilled the PDS requirements.Fig 3: Schematic representation of the Undertaker The materials that are to be used with the undertaker are still yet to be determined,however, some of the materials being considered are stainless steel (303 or 304), and titanium.Reasons for choosing the mentioned materials are described in more detail in the materialsselection. Page 12 of 14
  13. 13. As part of the final selection and materials a 3-D model and FEA (Finite ElementAnalysis) was conducted, see figures 5 and 6. With the aid of CAD(computer aid design) itbecomes more efficient to make any dimensional and modification changes. Using CAD andFEA analysis not only reduces cost and time but it also speeds up the development of the actualprototype. The 3-D model as seen in fig. 4 is an assembly of one of the prongs of the Undertaker,see fig. A. The material used in construction of the FEA analysis was stainless steel (303) andtitanium so that we can determine the amount of deflection under certain loading conditions.Fig. 4: Prong assembly of the Undertaker Page 13 of 14
  14. 14. FEA Analysis of Steel/ Titanium under a 2Lbs force:Fig 5: FEA analysis of steel (303) to determine the deflection under a certain loadFig 6: FEA analysis of titanium to determine the deflection under a certain loadUsing FEA software allows the team to get an idea on how a material will behave under certainload and from there we can then determine the areas of interest. Page 14 of 14
  15. 15. Material Considerations Some of the materials that have been considered for the actual prototype are stainlesssteel (303 and 304), Sylastic™, and titanium. All the mentioned materials are to be to resist tocorrosion and easy to sterilize. A breakdown how these materials could be used is as follows:  Swivel Joints: Stainless steel 304 balls are good resistance to corrosion  Tubing: Stainless steel 303 because it offers good strength, corrosion resistance and great mach inability.  Sylastic™: For the suction cups  Titanium: The body readily accepts titanium since it is more biocompatible than stainless steel and the machinability of titanium is comparable to most stainless steels.  PVC(plastic): Prototype The materials mentioned above each has its individual purpose, for example, the PVCwill be used in aid of constructing a working prototype since machining it is much easier andfaster as opposed to stainless steel or titanium. Page 15 of 14
  16. 16. Conclusion and recommendations: The winter term of 2003 was spent developing original solutions to the requirementsoutlined in the PDS. One best solution, the undertaker was chosen to be developed into a finaldesign. The design work completed in this term included computer modeling and FEA analysisof the stabilizing appendages. Next term should be spent finishing the design of the undertaker and constructing aworking prototype. This prototype will be tested in a mock-surgery with the Da Vinci surgicalsystem. It may also be tested on a live pig to further prove its worth. Our recommendations are to further develop the design into an integrated part of arobotic surgery system.Appendix: See attached papers/ Page 16 of 14