Design of a Minimally Invasive Surgical Teleoperated Master-Slave System with Haptic Feedback

Transcription

1 Design of a Minimally Invasive Surgical Teleoperated Master-Slave System with Haptic Feedback Linda van den Bedem, Ron Hendrix, Nick Rosielle, Maarten Steinbuch and Henk Nijmeijer Dynamics and Control Technology Department of Mechanical Engineering Technische Universiteit Eindhoven P.O. Box 513, 5600 MB Eindhoven, the Netherlands {L.J.M.v.d.Bedem, R.Hendrix, P.C.J.N.Rosielle, M.Steinbuch, H.Nijmeijer}@tue.nl Abstract Conventional Minimally Invasive Surgery (MIS) is performed with long and slender camera and instruments through at least three small incisions. However, it generally provides the surgeon with an uncomfortable body posture, limited force feedback and unnatural eye-hand-coordination. A masterslave system with force feedback is being developed, since such a system can overcome the inconveniences of MIS. This paper is about the design of the master and the slave. Index Terms Teleoperation, master-slave, minimally invasive surgery, haptic feedback, design I. TELEOPERATED MASTER SLAVE SYSTEM FOR MINIMALLY INVASIVE SURGERY In Minimally Invasive Surgery (MIS) the surgeon and possibly an assistant manipulate long and slender instruments outside the patient. The instruments enter the body cavity in which surgery is performed through small incisions. Performing surgery through small incisions has advantages for the patient, generally associated with the trauma related to accessing the field of surgery. However, it provides the surgeon with inconveniences, like the accompanying unnatural eye-hand-coordination. An incision also limits dexterity by reducing the number of available degrees of freedom (DoFs) at the instrument tip from the usual six or seven (if a gripper is applied) in open surgery to four or five (Fig. 1). Ports with seals are placed in the incisions to simplify exchange of instruments. However, feedback on applied forces is limited due to friction between instruments and seals and even can change during one procedure if the instrument gets humid (for example) [1]. The inconveniences that accompany MIS can be overcome by using a master-slave system which can even expand the type of MIS procedures possible (as mentioned in for example [2], [3]). Master-slave systems are being developed, which should provide the surgeon with natural eye-hand-coordination, an ergonomic position, dexterity and force feedback. Several closely The research of Hendrix on the master is supported by IOP Precision Technology, an innovation-driven research program of SenterNovem and the Ministry of Economic Affairs. Project partners are TNO and the Academic Medical Center AMC, University of Amsterdam; The research of Van den Bedem on the slave is supported by the Dutch Technology Foundation STW, applied science division of NWO and the Technology Program of the Ministry of Economic Affairs Fig. 1. Degrees of freedom (DoFs) of conventional instruments used for eye-surgery and endoscopic surgery: Φ, Ψ, Z, Θ and gripper if applicable related research projects are running (Fig. 2) to realize these systems for MIS. The haptic master is being developed within the scope of intraocular surgery, also called vitreo-retinal eyesurgery. However, the slave presented in this paper has its field of surgery in the abdomen and chest, laparoscopy and thoracoscopy respectively (further designated by the general term endoscopy). The main differences between these types of surgery are the size of the incisions and the field of surgery, which are directly related to the size of the instruments with diameter 0.6 mm for eye-surgery and 5 10 mm for endoscopy. Besides, the instruments used for visual feedback are a microscope and an endoscope respectively. But, since vitreo-retinal eye-surgery and endoscopy both use entry points to enter the field of surgery, have a similar range of rotation around this entry point and both projects aim for force feedback, it is believed that this master can be used for the slave for endoscopy as well. A master-slave system physically separates the surgeon from the field of surgery, since the surgeon operates the master that controls the slave, which actually performs surgery at the table. Therefore, these systems are called telemanipulators. However, since this master is initially being developed for eyesurgery tele is limited to about 50 cm. For eye-surgery the patient generally experiences only local anaesthesia, which means that the surgeon needs to be close to the patient s head, but this is not necessary for endoscopic procedures. As stated, the surgeon uses a microscope in eye-surgery, which provides stereoscopic information on the field of surgery. But visual information is limited to 2D in conventional endoscopy.

2 Fig. 2. Projects concerning the development of a teleoperated master-slave surgical system with force feedback for Minimally Invasive Surgery Reference [4] and users [5], [6] state that stereoscopic visual feedback should accompany the master-slave system since it improves the perception of the environment and makes performing endoscopic surgery easier, it could even be enhanced with multispectral information [7]. Additionally, according to [8] stereoscopic vision improves surgical performance. According to [9] a master-slave system consists of several subsystems: the mechanical (master and slave), the electronics, the servo-control and the high-level software subsystem. In this paper the mechanical subsystem will be discussed, regarding the design of the master (Section II) and slave (Section III). If performed, the evaluation of realized parts will be presented. An extensive evaluation of the whole system has just started (on subsystems), these evaluation results are not part of this paper. A. Introduction II. THE MASTER A preliminary design has been made for a haptic interface as part of a master-slave system to perform vitreo-retinal eye surgery [10]. As indicated in Fig. 1 an instrument for intraocular surgery can be manipulated in four DoFs around the entry point. Actuation of a gripper can be considered as the fifth DoF. Typical procedures are the removal of the vitreous humor (vitrectomy) and the removal of a membrane on top of the retina (membrane peeling). Operating room procedures show instrument movements of ±45 in Φ and Ψ direction, 360 for Θ and 25 mm in Z direction for these types of surgery. Sometimes manipulation of delicate intraocular tissue with a thickness of only 5 µm is required. Forces are most of the time below the detection limit which means that the surgeon must rely on visual feedback only. With the master-slave system, the surgeon will be provided with scaled force feedback and scaling of hand motion to deal with issues like tremor and the manipulation of delicate intraocular tissues. The basic idea is that by virtually placing the hands of the surgeon inside the eye of the patient a more intuitive working environment is created. This means that the end effector of the haptic device must have the same geometry and DoFs as the instrument used inside the eye. As mentioned before these DoFs are identical to conventional MIS and therefore the haptic interface can also be used for this type of robot assisted surgery. Fig. 3. A picture of one of two haptic pens. The motors for Θ-Z and the flat flexible conductors are not yet installed. The left device is a mirrored version. B. Realized haptic interface The haptic pen is based on a serial layout. As depicted in Fig. 3 four parts can be distinguished: Φ housing, Ψ housing, Θ-Z part and a button part. Direct drive is applied for Φ and Ψ to minimize friction. For the other three DoFs, a back drivable transmission is used due to the limited available space for the motors. All degrees of freedom are actuated by brushless DC motors in combination with sinusoidal commutation to minimize torque ripple. Encoders are used to measure the rotation of the motor shafts. In Fig. 3 also a support frame is depicted. This frame acts as coarse adjustment to pre-align the haptic interface with the instrument manipulator which is necessary to deal with different entry points. The length of the pen between rotation point (intersection point of the Φ, Ψ and Θ axes) and tip is set empirically to 150 mm. With this length, the rotation point is placed above the wrist joint of the operator. This layout is very comfortable for a movement in Φ and Ψ direction. To maintain this configuration during operation the Z range is limited. In Θ the pen will be rotated by rotating the wrist joint over a range of ±90. A jogging mode will be implemented to control the instrument in its whole Z and Θ range. As indicated in Table I, the resolution at the tip is higher than the resolution a surgeon can position his hand with (50 µm) [11]. The range in Φ and Ψ direction is made as large as possible and fulfills the requirements for eye surgery as well as endoscopy. The limitation of 88 in Ψ direction is set to prevent alignment of the Φ and Θ axes. The force levels of 3 N and 10 N are based on experiments and [12] where is stated that an index finger can exert 7 N and a middle finger 6 N without experiencing discomfort or fatigue. The continuous and maximum force levels also comply with the forces during endoscopy as can be seen in the requirements for the slave. Improvements that result from usability tests will be implemented in a second version of the haptic pen.

3 TABLE I PROPERTIES FOR THE DIFFERENT DOFS OF THE REALIZED HAPTIC PEN MEASURED AT THE TIP Φ Ψ Θ Z Button Range ±90 88 /45 ±175 ±8 mm 5 mm Resolution 30 µm 30 µm 0.1 mrad 1.8 µm 20 µm Continuous 3N 3N Nm 2.4 N 3.5 N force/torque Maximum 10 N 10 N 0.65 Nm 32 N 7N force/torque III. THE SLAVE A. Introduction The slave will have its field of application in laparoscopy and thoracoscopy (endoscopy). A study has been performed on procedures performed in these fields, to gain insight in the requirements of the robot as was already mentioned in [13]. The procedures considered were based on descriptions [14] and on (partially) comparable mainly laparoscopic observed procedures. The latter procedures were generally performed by or under supervision of [15], either with or without the da Vinci telesurgery system [16]. From the study on MIS procedures and discussions with several surgeons, it was concluded essential to connect the slave to the operating table. This enables the team to adjust the table during the procedure, without the need to change the set-up of the slave as well. Besides, the slave can be adapted to the patient and procedure at hand because of its modular layout. Its main modules (Fig. 4) are: the pre-surgical set-up and the three manipulators. The presurgical set-up is used to position and orient the manipulators and consists of the platform-adjustment, the platform and three manipulator-adjustments. The manipulators are used to move the instrument/endoscope during surgery. Forces executed with or on the instruments need to be measured since the masterslave system is haptically assisted. B. Requirements A literature study on load levels at the tip of the instrument [17] in robotic surgery establishes the following values for endoscopy: Nominal load F n of 2.5 N (needle driving, cutting) while able to rotate the tip 180 in half a second (rough estimate). Suture tying load F t of 5 N at standstill. In [18] it is stated that several Newtons are required to securely tie a suture, in [19] tying forces range from 1 5 N for various types of sutures. Peak load F p of 10 N at standstill, which is based on a maximum suture tying force at the tip of 8.9 N in [3] and 6 7Nin[20]. The smallest noticeable force should be 0.06 N [21]. A nominal gripper load of 10 N should be able to securely hold a needle. The gripper peak load is set to 20 N. This value lies between the maximum gripper force of Fig. 4. Modular layout of the slave: pre-surgical set-up and manipulators for instrument/endoscope. The pre-surgical set-up consists of: 1 platformadjustment, 1 platform and 3 manipulator-adjustments the instrument of 50 N in [3], of 40 N in [20] and the gripping force of about 10 N in [18]. The required bandwidth of the slave system strongly depends on the tasks the human operator needs to perform. Primarily the operator needs to perform accurate movements with the slave system during surgical procedures. Ref. [22], [8] states that 99% of the frequency content of accurate motion by the surgeon is in the 0 2Hzregion.Whereas involuntary motion like tremor, is in the 8 10 Hz region [23]. Furthermore, this slave system is intended to measure forces. Forces are kinesthetically sensed by the operator up to 20 Hz, whereas for example a surface texture is sensed cutaneously from Hz (among others stated in [23], [24]). The bandwidth of the position control of the slave system is set to be at least 20 Hz and the frequency content of the force measurements is set to be at least 60 Hz. The instrument will have an initial position and orientation before surgery starts. With respect to this initial orientation it will have to rotate ±30 in Φ and Ψ, translate 300 mm in Z and rotate desirably more than ±180 in Θ to reach its complete field of surgery. For precise surgical procedures a position resolution of 50 µm of the tip of the instrument is required [11]. C. Pre-surgical set-up A sub-system used for accurate movements between parts of this system, should aim for a short force-path between these parts [25]. A short force-path can lead to a relatively stiff and light design compared to a system with a larger forcepath, which is advantageous for its dynamic behaviour and therefore for the force measurement. To this end the platformadjustment is connected to the table and is used to move and then fix the platform relative to the table, close to the incisions by means of Θ 1, Ψ 1 3 and Θ 2 (Fig. 5). It results in a short force-path between the platform and its reference (the table top plus patient). The position of the manipulator-adjustments within the platform is based on the mean distance between the surgeon s instruments and the endoscope for laparoscopic procedures (Fig. 5). Since the platform will be near the field

4 Fig. 5. Platform-adjustment of the pre-surgical adjustment, which is connected to the table and used to position and fix the platform close to the field of surgery by means of Θ 1, Ψ 1 3 and Θ 2. The manipulator-adjustments have a mutual distance within the platform of 80 mm (mean distance between endoscope and the surgeon s instruments in laparoscopic procedures). Fig. 6. DoFs used to position and orient the manipulators relative to the mean distances between the incisions of surgery, the reach required of the manipulator-adjustment to position and orient the actual manipulators will be based on anatomical differences between patients and will thus be small [26]. This results in a short force-path between the instrument tips as well (Fig. 7). The manipulator will initially be positioned and oriented by means of the Θ 1 and Ψ 1 3 of the manipulator-adjustments and by the Φ of the manipulator itself (Fig. 6). These DoF are almost similar to the DoF of the platform-adjustment. D. Manipulator for instrument/endoscope The manipulator moves the instrument in Φ, Ψ, Z and Θ during surgery, according to the DoFs in Fig. 1. The instrument itself has a gripper plus at least two more DoF at the end of its main shaft, to provide the surgeon with dexterity. Then the system has the usual six DoF plus gripper available at the instrument tip, a similar number compared to manipulating instruments in open surgery. The DoFs of the manipulator will not be backdriveable except for Φ, since this one is used for the manipulatoradjustment as well. With loss of power, the first mentioned DoFs will remain in position, an inherent safety. It will still be possible to remove the manipulator from the surgical site since this is done with the mechanical manipulator-adjustment. The sensors to measure the forces executed with the instrument in Φ and Ψ will not be placed near the tip of the instrument to limit risks for the patient. The torque sensors are placed just after the transmissions of the respective DoF, to prevent measurement of the transmission friction. They consist of an elastic element with a displacement sensor and have a range from Nmm, corresponding to N at the instrument tip. The torque sensors are currently being evaluated regarding range, resolution and accuracy. Another purpose of the instrument manipulator is to limit post-operative pain related to access trauma. Therefore, the instrument manipulator will support the instrument/endoscope in all its DoF to reduce the forces executed on the tissue (also mentioned in for example [3]). As shown in Fig. 1 the Fig. 7. Short force-path between the instrument tips (dotted line), by positioning the platform close to the field of surgery. instrument rotates around its incision point. But an actual hinge can not be applied for this rotation point since the diameter of the incision is limited. Therefore, this required rotation point is kinematically fixed by a double parallelogram construction (among other methods described in [27], [3], see Fig. 8 and 9) and has to coincide with the incision during surgery. The Φ-movement can be more than ±180 but is limited to prevent damaging the cables of the Ψ-drive. The Ψ-movement of the manipulator is ±35 with respect to its neutral position. The first identification of the Φ-axis of the manipulator was performed by applying a sine-function with white noise superposed, to remove the effect of Coulomb friction. As expected the resulting Bode-plot in Fig. 10 shows that the system can be modelled as a mass-spring system. The estimated inertia of the manipulator for the Φ-axis at the kinematically fixed rotation point P is kgm 2. Rotation of the instrument around this axis is measured at the motor-side. From the fact that the actuator and sensor are collocated, from the order of the anti-resonance/resonance, it appears that some mass uncouples at f 30 Hz. This frequency should be raised to be well above the 20 Hz set, which can be realized for example by reducing the mass of parts that are at a large distance from the Φ-axis.

5 Fig. 8. Instrument manipulator to manipulate the instrument in Φ, Ψ, Z and Θ. Its double parallelogram realizes a kinematically fixed point P of rotation that should coincide with the incision during surgery. Fig. 9. Realized instrument manipulator. The kinematically fixed rotation point P should coincide with the incision during surgery. Here a ΘZ-dummy substitutes the respective manipulator. The ΘZ manipulation of the instrument will be realized by means of a friction wheel drive. The housing of the friction wheels for the Z-translation of the instrument is being rotated for the Θ-rotation of the instrument, which results in a compact design. The transmission-ratios amount to approximately 200 for both the Θ and Z DoF and are not backdriveable. The Z-stroke of the instrument is limited by the length of the instrument and will be 300 mm, the Θ-rotation will be limited to ±180. It is not set that the joints of the instrument tip will be aligned with the main instrument shaft at power loss. If the instrument tip is not aligned with its main shaft it could get stuck in the ports on removal. Therefore, the hinges of the instrument will have to be backdriveable (a similar discussion can be found in [3], [28]). IV. FUTURE Each haptic pen of the master is provided with five DoF, since the master is developed for eye-surgery. Two or three DoF of the slave thus remain to be controlled. This can be realized by using the same DoFs of the master in different control modes (coarse and precise range for example), which will be implemented and tested. V. CONCLUSION The haptic master intended for eye-surgery has an adjustment to position and orient its haptic pens initially. Each haptic pen currently has five DoF: Φ, Ψ, Z,Θ and a button. Each of the five DoF is being actuated to provide the surgeon with force-feedback. The slave for laparoscopic and thoracoscopic surgery, has one platform positioned near the field of surgery. Each manipulator is being positioned with respect to this platform and its intended incision with its manipulator-adjustment. Each manipulator moves an instrument or endoscope in Φ, Ψ, Z and Θ. The properties for the different DoFs of one haptic pen match with the required properties to operate one instrument manipulator and feedback a scaled equivalent of the measured forces. ACKNOWLEDGMENT R. Hendrix thanks J. Grasman, L. van Leeuwen and J. Bulsink who have created the experimental hardware of the master. L. van den Bedem thanks M. Janszen, S. Plukker R. van Aaken and K. van Dijck who are and have been creating the hardware of the slave. REFERENCES [1] J. van den Dobbelsteen, A. Schooleman, and J. Dankelman, Friction dynamics of trocars, Surgical Endoscopy, vol. 21, no. 8, pp , August [2] J. Chen, E. Haas, and M. Barnes, Human performance issues and user interface design for teleoperated robots, IEEE Transactions on systems, man, and cybernetics - Part C: Applications and Reviews, vol. 37, no. 6, pp , November [3] A. Madhani, Design of teleoperated surgical instruments for minimally invasive surgery, Ph.D. dissertation, Massachusetts Institute of Technology, [4] M. Ferre, R. Aracil, and M. Sánchez-Urán, Stereoscopic human interfaces, advanced telerobotic applications for telemanipulation, IEEE Robotics and Automation Magazine, vol. 15, no. 4, pp , December [5] I. Broeders, Department of Surgery Meander Medical Center; Twente University, Institute of Technical Medicine; the Netherlands, , private communication. [6] J. Maessen, Department of Cardio-Thoracic Surgery, academisch ziekenhuis Maastricht, the Netherlands, , private communication. [7] December [8] J. Byrn et al., Three-dimensional imaging improves surgical performance for both novice and experienced operators using the da vinci robot system, The American Journal of Surgery, vol. 193, no. 4, pp , 2007.

6 Magnitude [db] Phase [deg] Frequency f [Hz] telesurgery: second generation berkeley/ucsf laparoscopic telesurgical workstation and looking towards the future application, Industrial Robot: An International Journal, vol. 30, no. 1, pp , [21] L. Jones, Kinesthetic sensing, in Human and Machine Haptics, MIT Press. MIT Press, [22] B. Hannaford, Experimental measurements for specification of surgical mechanisms and understanding of surgical skill, in Lecture Notes of the European Summer School on Surgical Robotics, September [23] G. de Gersem, Kineasthetic feedback and enhanced sensitivity in robotic endoscopic telesurgery, Ph.D. dissertation, Katholieke Universiteit Leuven, [24] H. Tan, M. Srinivasan, B. Eberman, and B. Cheng, Human factors for the design of force-reflecting interfaces, ASME Journal of Dynamic Systems and Control, vol. 55, no. 1, pp , [25] P. Rosielle, Constructieprincipes, lecture note 4007, Technische Universiteit Eindhoven, Tech. Rep. [26], Surgical robot, November 2007, patent WO/2007/ [27] R. Taylor and D. Stoianovici, Medical robotics in computer-integrated surgery, IEEE Transactions on Robotics and Automation, vol. 19, no. 5, pp , October [28] U. Hagn et al., Telemanipulator for remote minimally invasive surgery, requirements for a light-weight robot for both open and laparoscopic surgery, IEEE Robotics and Automation Magazine, vol. 15, no. 4, pp , December Frequency f [Hz] Fig. 10. Bode-plot of identification of the Φ-axis of the manipulator. The inertia of the system is estimated to be kgm 2. [9] S. Charles et al., Dexterity-enhanced telerobotic microsurgery, in ICAR, July [10] R. Hendrix, P. Rosielle, and H. Nijmeijer, Design of a haptic master interface for robotically assisted vitreo-retinal eye surgery, ICAR 2009, 2009, in press. [11] C. Riviera, R. Rader, and P. Khosla, Characteristics of hand motion of eye surgeons, in Proceedings of the 19th International Conference of the IEEE Engineering in Medicine and Biology Society, Chicago, 30 October 2 November [12] C. Smith, Human factors in haptic interfaces, Crossroads, the ACM Student Magazine, vol. 3, no. 3, pp , January [13] L. van den Bedem, N. Rosielle, and M. Steinbuch, Design of a slave robot for laparoscopic and thoracoscopic surgery, in Electronic Proceedings 20th International Conference of Society for Medical Innovation and Technology, document F 016, [14] [15] I. Broeders, observed procedures, Universitair Medisch Centrum Utrecht (UMC Utrecht), the Netherlands, , private communication. [16] da vinci surgical system, Intuitive Surgical, Sunny Vale, CA, USA. [17] K. van Dijck, Design of a 4-dof minimally invasive instrument for haptic robotic surgery, Master s thesis DCT , Technische Universiteit Eindhoven, 2008, confidential. [18] U. Seibold, B. Kuebler, and G. Hirzinger, Medical Robotics. I- Tech Education and Publishing, 2008, ch. Prototypic force feedback instrument for minimally invasive robotic surgery. [19] M. Kitagawa, D. Dokko, A. Okamura, and D. Yuh, Effect of sensory substitution on suture-manipulation forces for robotic surgical systems, The Journal of Thoracic and Cardiovascular Surgery, vol. 129, no. 1, pp , [20] M. Çavusogglu, W. Williams, F. Tendick, and S. Sastry, Robotics for