Surg Endosc DOI 10.1007/s00464-014-3534-6
and Other Interventional Techniques
A single port laparoscopic surgery robot with high force transmission and a large workspace Byungsik Cheon • Erkin Gezgin • Dae Keun Ji Morimasa Tomikawa • Makoto Hashizume • Hong-Jin Kim • Jaesung Hong
•
Received: 21 August 2013 / Accepted: 31 March 2014 Ó Springer Science+Business Media New York 2014
Abstract Introduction This study presents the design of a novel single port laparoscopic surgery robot that is actuated by plate-spring-driven mechanisms with high force transmission and a larger workspace. Many ongoing studies aim to develop robotic single port laparoscopic surgery platforms due to the potential advantages in terms of a short recovery period and fewer postoperative scars. Most of these investigations of single port access have focused on resolving the inconvenient maneuverability of manual single port laparoscopic surgery. However, drive mechanism structures are another requirement. Materials and Methods Most of the existing robotic platforms cannot transmit sufficient force, as many of them use wire-driven mechanisms, which are prone to mechanical deformation that also negatively affects the accuracy of the end effector. In addition, even the best-known
laparoscopic surgical robot system has instruments with a limited workspace for single port laparoscopic surgery. Therefore, the purpose of this study was to propose a novel robotic single port laparoscopic surgery platform that uses plate springs to transmit higher forces during tissue handling. Results and Conclusion Compared to wire- or link-driven mechanisms, the plate-spring mechanism provided surpassing force transmission, with [14 N force transmission achieved, which enables most laparoscopic surgery with single port access. In addition, the high degree of freedom structure of the proposed design permitted an expanded workspace, which might be the most competitive characteristic among the single port systems reported to date.
Electronic supplementary material The online version of this article (doi:10.1007/s00464-014-3534-6) contains supplementary material, which is available to authorized users.
Laparoscopic surgery is one of the most successful medical applications that have emerged since the end of the last century. By opening tiny incisions on the abdominal surface, laparoscopic surgery allows surgeons to operate inside the body using specialized laparoscopic instruments. Operations result in less blood loss, reduced postoperative scaring, fewer complications, and faster recovery compared with those of standard open surgery [1]. As the potential of methods has been realized through their successful implementation, continuous efforts have been made to reduce the number of incisions needed. Consequently, natural orifice transluminal endoscopic surgery (NOTES) and single port laparoscopic surgery (SPLS) have been proposed. Although these methods have similarities, such as their minimal invasiveness, NOTES uses a natural orifice entry and an incision inside the body,
B. Cheon E. Gezgin D. K. Ji J. Hong (&) Department of Robotics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Korea e-mail: [email protected] E. Gezgin Department of Mechatronics Engineering, Izmir Katip Celebi University, Izmir, Turkey M. Tomikawa M. Hashizume Department of Advanced Medical Initiatives, Faculty of Medical Sciences, Kyushu University, Fukuoka, Japan H.-J. Kim Department of HBP Surgery, Yeungnam University Hospital, Daegu, Korea
Keywords Single port laparoscopic surgery Plate spring Robotic surgery
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whereas SPLS uses a single incision on the abdominal surface, preferably the navel. However, several problems remain unsolved, and difficulties have been reported in clinical NOTES trials [2–4]. As a result, SPLS procedures are increasing in both popularity and feasibility, and are considered a possible alternative to conventional laparoscopic surgery [5, 6]. The merits of multi-port and single port surgery are debated. As Marks et al. [7] reported, the advantages of single port surgery have not been demonstrated sufficiently in terms of blood loss, complications, or pain scores. It also requires longer operating times, although the cosmetic score is higher. Therefore, careful consideration is required when choosing single port laparoscopic surgery instead of multiport access. The proposed robot might contribute when the single port access procedures are selected. If the issues of single port laparoscopic surgery are overcome by the development of new instruments, such as the proposed system, the number of such surgeries will increase. The first single port laparoscopic surgery was reported in 1998 by Esposito [8]. Since that trial, novel instruments and specialized techniques have been developed to overcome the technical limitations due to its use of traditional laparoscopic instruments in a single incision [9, 10]. Thanks to these developments and much scientific research, many clinical operations can be carried out with a single incision, such as cholecystectomy, appendectomy, hysterectomy, tubal ligation, ovarian cystectomy, nephrectomy, partial nephrectomy [11], ureterolithotomy [12], and prostatectomy. Nevertheless, surgeons remain reluctant to perform single port laparoscopic surgery, as technical challenges remain. The most typical of these, counter-intuitive usage, in which the procedure is conducted using crossed laparoscopic instruments to increase operative workspace, confuses the sense of right–left direction. Long periods of intense concentration are required during operations to prevent physical contact between the laparoscopic instruments [13–15]. In addition, the surgeon’s visibility is likely to be limited, as laparoscopes and other medical instruments are aligned in the same direction [1]. Due to this problem, surgeons have difficulty securing a sufficiently clear view to manipulate surgical instruments. The use of robots as an alternative approach to overcome these problems is becoming more popular. Using master and slave systems makes it easy to overcome counter-intuitive usage and conduct precise operations. Moreover, it is possible to use enhanced vision systems to eliminate visibility issues. In contrast, as a robot manipulator must enter the body from a single port, its size, transmission, and parallel orientation to the workspace are becoming serious constraints.
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In response to these limitations, two major configurations have been proposed: the ‘‘X type’’ and ‘‘Y type.’’ Type X SPLS robots use a standard manual entry configuration, in which instruments controlled by individual serial robot manipulators enter the body from a single incision. Although the counter-intuitive operation problem is solved by means of master–slave control [16], and force transmission is sufficient, these robots have drawbacks including external arm collisions, large size, and relatively large incision size requirements. A SPLS robot designed by Horise et al. [17] is an example of the X-type robots under development. Type Y SPLS robots have two states. They enter the body in an ‘‘I’’ configuration from a single incision; once inside the body, they transform into a ‘‘Y’’ shape by opening two existing arms [18]. This procedure prevents possible arm collisions during operations, expands the effective workspace, and reduces the overall size, including the incision diameter. Despite its manual passive controls, the SPIDER system is the most similar to a SPLS robot, and represents the transition between a passive device and a robotic system for SPLS. It has been used clinically after gaining FDA approval [19]. As the SPIDER system uses wires for forceps manipulation, it is difficult to handle heavier payloads, so it is more appropriate for a limited range of operations, such as gastric band and gastric sleeve surgery. IREP, another snake-like robot with a 14 degree of freedom continuum, was developed for SPLS [20]. IREP is one of the smallest SPLS robots available and has advanced motion dexterity. However, it also has limits in terms of conducting general surgical operations with a large payload capacity. SPRINT, developed by Piccigallo et al. [21], has one of the highest force transmission capabilities among its rivals. This robot has six degrees of freedom in its single arm, and on-board motors and gear boxes within its arm segments, yet a larger incision diameter is required due to the size of the arms. Other examples include stackable four-bar manipulators [22], and a design using flexible shafts in its motion transmission that transmits substantial force values without using wires [23, 24]. However, both have limited manipulation capabilities. Considering all of the strengths and weaknesses of the previous studies, we propose a novel Y-type robotic SPLS platform design that transmits relatively higher force during tissue handling by incorporating plate springs in the structure. In addition, the high degree of freedom design structure permits an expanded workspace, which enables operations across a wide surgical area without changing the system setup.
Surg Endosc
Fig. 1 Plate spring under compression with and without guides. The plate spring with appropriate guides can deliver a compressive force that is cannot be realized by wires
Design
Fig. 2 Differences in the assemblies of wires and a plate spring: dual and single assembly
We set the design specifications in terms of size, force transmission, and robot structure. Thus, it is important to clarify the main constraints and goals of the design. The stem must adhere to a diameter \25 mm to avoid scar formation and reduce wound pain. The second constraint is a result of the force requirements of surgical procedures. According to Richards et al. [25] and Lazeroms et al. [26], a force range of ±10 N on the forceps tool tip is appropriate. Last, a dual-arm Y-type robot manipulator structure was to have six degrees of freedom in each arm to expand the workspace and avoid collisions. Plate-spring-driven structure As mentioned previously, the greatest problem with SPLS robots is their size limitation, which creates difficulties with force transmission between the actuators and forceps. The trade-off between the volume of the transmission structures and their force transmission capabilities requires an optimal design solution. In contrast to the bulkiness of gearboxes and the weaknesses of wired systems, plate springs have the optimum specifications in terms of design constraints. Similar to wires, they can transmit tension from the actuators and the end effector. However, they have the unique property of being able to deliver compressive forces provided that they are assembled inside the guides (Fig. 1). As a result, a single force for pull or push is sufficient, whereas two pulling forces are required for motion using a wire-driven mechanism (Fig. 2). In addition, having a larger crosssectional area provides relatively greater force transmission compared with those of wires. Besides, its compact size greatly reduces the volume occupied by the transmission mechanism, contrary to gearboxes or links. Notably, the
Fig. 3 Plate springs: assembly on the dual arms of the first prototype mechanism
large surface-contact area between the plate spring and the guide increases friction. As a result, lubrication or lowresistance materials should be used inside the guides. The actual assembly of the plate springs can be seen in the first prototype mechanism shown in Fig. 3. The platespring mechanism was applied for joint 3, the joint used most frequently, and the one requiring greater force. Workspace and degree of freedom considerations Generally, type Y SPLS robots are incapable of operating on relatively large organs, such as the liver and intestines, because of the fixed starting point of the two arms, where they open to expand the workspace. Unlike the type X robots, this disadvantage prevents creation of a long stroke between the ends of laparoscopic forceps. To overcome this constraint, a long stroke is ensured by separating the starting point by two individual prismatic joints for each arm. Additionally, this added degree of freedom provides a
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Surg Endosc Fig. 4 Comparison of workspace configurations and possible postures: X type, Y type, and modified Y type SPLS robots with additional prismatic joints
Fig. 5 Three-dimensional model of an average size, 3,000 cm3 CO2insufflated human body
SPLS robots. A total of 12 degrees of freedom is achieved after adding the overall mobility of the two individual arms. After the structural synthesis and prior to deciding the robot manipulator construction parameters, the average size of the human body was modeled using three-dimensional (3D) modeling software and taking into consideration the classical SPLS, in which approximately 3,000 cm3 CO2 is insufflated into the abdominal cavity (Fig. 5). A coarse robot manipulator model was assembled in a virtual environment after constructing a soft working environment (Fig. 6), and pre-construction parameters were controlled so they could be refined after the kinematic analysis. Mechanical implementation
Fig. 6 Three-dimensional model of the coarse manipulator and virtual working environment
larger, more efficient workspace with increased postural possibilities for the forceps (Fig. 4). The remaining mobility of the robot manipulator is determined by preserving the four degrees of freedom of classical laparoscopy and the one native degree of freedom to open the arms from the classical configuration of type Y
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A final prototype-ready model was prepared using 3D modeling software following the workspace analysis and determination of the construction parameters. The proposed robot was named ‘‘PLAS,’’ which stands for PLAteSpring mechanism-based LAparoscopic Surgery robot. As seen in Fig. 7, PLAS is composed of two main sections. The first section includes the robotic arms that will conduct the surgical operations and the stem of the robot that will enter the human body from a single incision. The second, actuation, section includes all of the distinct actuators that will confer 12 degrees of freedom. The actuation section of the robot always remains outside of the body. The main stem is designed to be cylindrical to preserve existing trocar compatibility. Trocars are the introducers that enable subsequent placement of surgical instruments
Surg Endosc Fig. 7 Structure of the proposed single port laparoscopic surgery (SPLS) robot: PLAS
motion of the fourth revolute joint is actuated using wires. The motions of the left arm and their responsible actuators are shown in Fig. 10. After completing the 3D modeling, a final PLAS prototype was manufactured and assembled (Fig. 11) for use in laboratory and animal experiments.
Fig. 8 Cross section view of PLAS
Fig. 9 Left arm configuration of PLAS. Right arm has an identical structure
without a CO2 leak. The stem of the manipulator holds the passages for laparoscopes, forceps, plate springs, wires, and the robotic arms (Fig. 8). Each arm of PLAS has six degrees of freedom, including two prismatic and four revolute pairs (Fig. 9). The grasping motion of the end effector is excluded from the degrees of freedom calculation, and the out-of-plane
Potential surgical task The PLAS robot can be used to perform various surgical tasks required for general laparoscopic surgery. These tasks include lifting the liver, holding tissue, cutting tissue, etc. It has been difficult to perform laparoscopic surgery via a single port because the instruments for SPLS do not have sufficient workspace or exert sufficient force to handle the tissue [19]. Accordingly, an operation must be performed in a restricted area, and the setup must be repeated when the surgical site is moved during the surgery [27]. In addition, the size and weight of tissue that can be held are limited owing to the insufficient force of the instrument. The PLAS robot has advantages in terms of the force and task area. It covers a larger workspace than the da Vinci system [27] and enables greater force than the SPIDER system [19]. If a single port laparoscopic surgery robot can guarantee sufficient force and task area, most laparoscopic surgery could be replaced by single port laparoscopic surgery. Figure 12 shows the basic configuration of a surgical task for partial hepatectomy with PLAS. PLAS has a hole for inserting a flexible endoscope, but does not have an additional supporting structure to hold the endoscope. A tool change is also impossible with the current version of PLAS. Therefore, several ports and forceps might be
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Fig. 11 Final prototype of PLAS
Fig. 12 A possible setup of PLAS for partial hepatectomy
Fig. 10 Various joints and corresponding motions of the left arm
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required to perform an entire procedure, such as a laparoscopic hepatectomy. PLAS can hold and move tissue ranging in size from a small piece to the entire right or left lobe of the liver. If another instrument were available, it could be used for coagulation, clipping, or other operations, while PLAS is
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Fig. 13 The large task area of PLAS for liver resection
holding the liver tissue. Alternatively, if another forceps can hold the liver and make sufficient task space, PLAS can be used for cutting and clipping the tissue or blood vessels. When using extra instruments, PLAS functions more efficiently than other instruments, so that the number of necessary incisions is reduced to a minimum. The current version of PLAS has two types of instrument installed: for grasping and cutting. The next version of PLAS might include an automatic or semi-automatic tool change function, as well as an endoscope-holding structure distally. PLAS can be used most efficiently for laparoscopic surgery requiring a large workspace, such as for laparoscopic hepatectomy. A cholecystectomy or appendectomy can be performed relatively easily by other single port surgery robots, such as the da Vinci and SPIDER systems. We developed PLAS with the goal of performing more difficult surgeries, such as laparoscopic hepatectomy. Figure 13 shows the workspace of PLAS for liver resection. The prismatic joint allows the arms of PLAS to be spread wide, and maintains the distance between the arms. This allows PLAS to cut a large area of liver tissue without changing the robot pose or setup. No other commercial system covers as large an area.
Table 1 Force transmission experiment setup details Joint i
PLAS arm posture
Force gage tip distance (mm)
1
Straight
–
2
Angled
60
3
Angled
15
4
Angled
15
5
Straight
–
6
Angled
20
Grasping
Straight
15
Fig. 14 Force transmission measured at each joint using a force gage
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Surg Endosc Fig. 15 Experimental setup for measurement of position repeatability with various payloads
Experiments and results After assembling the PLAS, a series of laboratory and field experiments were carried out to verify the force transmission capabilities of the joints and end-effector position repeatability. The first laboratory test was conducted using a force gage that was fixed firmly onto a vibration-free table using the magnetic base. Measurements were taken from each of the joints, which were actuated individually during five trials. The details of the experimental setup including the force gage tip distance measured from the rotation axis of the related joints and the posture of the PLAS arm are shown in Table 1. The results for each configuration are shown in Fig. 14. Because the left arm has the same structure and performance as the right arm, only the right arm of PLAS was used in the trials. The second laboratory test was conducted using the PolarisÒ optical tracking system which is a product of NDI (Canada, Ontario, Waterloo). End-effector positions were tracked by PolarisÒ under the actuation of joint 3 to evaluate the repeatability of the end-effector positions and the reliability of the plate-spring drive under predefined loads. Infrared reflectors were attached to the end effector to provide a position tracking reference, and a weight
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counterbalance with a pulley was used to simulate payload (Fig. 15). We determined a fixed trajectory to evaluate available payload. Eight experiments were conducted under loading conditions with 200, 400, 600, 800, 1,200, and 1,600-g weights, in addition to an experiment with no payload. Each loading condition was subjected to five trials and the results were collated (Fig. 16). The PLAS trajectory remained constant until 1,400 g, but a normal PLAS trajectory was not obtained at 1,600 g. After the laboratory test trials, an animal experiment was conducted using animal subjects and living tissues with the permission of the animal experiment review committee of Kyushu University and under the supervision of expert surgeons (Fig. 17). The surgeon performed a liver dissection using PLAS and determined that it has sufficient force transmission capability to handle the organs during surgery.
Discussion The first PLAS prototype outperformed its rivals. The results were promising in terms of force transmission capabilities and workspace availability.
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Fig. 17 Animal experiments under the supervision of expert surgeons. Cutting of liver tissue was performed in a pig
Fig. 16 Trajectories moved with various payloads
The force gage experiments revealed that PLAS had margins sufficient to achieve the 10-N goal at the forceps, even with single contributions from all joints, with the
exception of joint 4. For example, readings taken 15 mm away during the plate-spring trial actuating joint 3 (Fig. 16) showed that to achieve the force transmission goal of 10 N at the forceps using only joint 3, summation of the variable parameter d5 and design parameter d6 (Fig. 7) should not exceed 50 mm; this was readily achievable using the control algorithm. If larger workspaces and higher forces are required, the required force can be supplied by other actuators. The wire-driven and off-plane structures of PLAS joint 4 result in the weakest force transmission capability, and it should be refined using either another spring drive or an alternative mechanism in future prototypes. Evaluation of the reliability and repeatability of the proposed plate-spring actuation under various loading conditions showed that the paths of the forceps remained uniform even at higher loadings up to 1,400 g.
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These results suggest that the plate-spring drive is a promising alternative for SPLS robot design. Furthermore, field experiments on animal subjects and living tissues demonstrated that PLAS reaction speeds, force transmission capabilities, maneuverability, and workspace configurations are suitable. In an animal experiment, the force used to handle tissue was appropriate. It was sufficient to handle the entire liver or just a small tissue segment during the surgery. Despite the considerable force used, no tissue damage occurred. The robot has a stronger force than other single port robots, but does not exceed that of multi-port robots, such as da Vinci system. Therefore, it is considered to be at least as safe as da Vinci system. The robot does not have haptic function. This might cause some problems, as with da Vinci. Many surgeons believe that tissue damage can be avoided by making use of the visual information in the endoscopic image. Haptic function might be dealt with as a separate topic in future research. The structure of the PLAS prototype should also be mentioned with respect to the predefined goals. The Y-shaped configuration of PLAS resolved the problem of counter-intuitive operation of single port laparoscopic surgeries, and adding prismatic joint 1 to the structure solved the workspace weaknesses of Y-type structures. We constructed the prototype from aluminum, rather than originally planned stainless steel, to make its manufacture easier and cheaper [28]. Thus, the diameter of the main stem had to be increased to 33 mm to meet the stiffness requirement. Although this value was lower than those of other SPLS robots [21], exchanging aluminum for a stiffer material in future prototypes will facilitate manufacture of instruments with main stem diameters \25 mm.
Conclusions In conclusion, we constructed a novel single port surgical robot named PLAS that achieved the desired increase in force transmission capability and workspace volume by utilizing a novel plate-spring-driven design. The results of both laboratory and animal experiments were promising and will be enhanced further in future prototypes. Although additional functions, such as a laparoscope holder, and various instruments are required for clinical use, PLAS provides a possibility for increasing the use of single port laparoscopic surgery. Acknowledgments We appreciate the advice from the Prof. WooJung Lee at Yonsei University, and we appreciate the helpful comment and idea by Prof. Takeshi Ohdaira at Kyushu University. We also appreciate the help for paper organization by Prof. Pyung Hun Chang at DGIST. Mr. Seongbo Shim who is a Master student at
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surgical robotics lab., DGIST also helped greatly for the revision of the paper. This work was supported in part by the DGIST MIREBraiN Program, the R&D Program of th DGIST Convergence Science Center (12-BD-0402), and the Health and Medical R&D Program of the Ministry of Health and Welfare of Korea (HI13C1634). Disclosures Mrs. Byungsik Cheon, Erkin Gezgin, Dae Keun Ji, Morimasa Tomikawa, Makoto Hashizume, Hong-Jin Kim, and Jaesung Hong have no conflicts of interest or financial ties to disclose.
References 1. Lee W-J (2010) Single port laparoscopic surgery. J Korean Med Assoc 53(9):793–806 2. Gettman MT, Lotan Y, Napper CA, Cadeddu JA (2002) Transvaginal laparoscopic nephrectomy: development and feasibility in the porcine model. Urology 59(3):446–450 3. Clayman RV, Box GN, Abraham JB et al (2007) Rapid communication: transvaginal single-port NOTES nephrectomy: initial laboratory experience. J Endourol 21(6):640–644 4. Lima E, Rolanda C, Pego JM et al (2007) Third-generation nephrectomy by natural orifice transluminal endoscopic surgery. J Urol 178(6):2648–2654 5. Autorino R, Cadeddu JA, Desai MM et al (2011) Laparoendoscopic single-site and natural orifice transluminal endoscopic surgery in urology: a critical analysis of the literature. Eur Urol 59(1):26–45 6. Raman JD, Cadeddu JA, Rao P, Rane A (2008) Single-incision laparoscopic surgery: initial urological experience and comparison with natural-orifice transluminal endoscopic surgery. Br J Urol Int 101(12):1493–1496 7. Marks J, Tacchino R, Roberts K, Onders R et al (2011) Prospective randomized controlled trial traditional laparoscopic cholecystectomy versus single-incision laparoscopic cholecystectomy: report of preliminary data. Am J Surg 201(3):369–373 8. Esposito C (1998) One-trocar appendectomy in pediatric surgery. Surg Endosc 12(2):177–178 9. Dhumane PW, Diana M, Leroy J, Marescaux J (2011) Minimally invasive single-site surgery for the digestive system: a technological review. J Minimal Access Surg 7(1):40–51 10. Autorino R, Stein RJ, Lima E et al (2010) Current status and future perspectives in laparoendoscopic single-site and natural orifice transluminal endoscopic urological surgery. Int J Urol 17(5):410–431 11. Kaouk JH, Goel RK (2009) Single-port laparoscopic and robotic partial nephrectomy. Eur Urol 55(5):1163–1169 12. Gettman MT, White WM, Aron M et al (2011) Where do we really stand with LESS and NOTES? Eur Urol 59(2):231–234 13. Kaouk JH, Goel RK, Haber GP, Crouzet S, Stein RJ (2009) Robotic single-port transumbilical surgery in humans: initial report. Br J Urol Int 103(3):366–369 14. Autorino R, Cadeddu JA, Desai MM et al (2011) Laparoendoscopic single site and natural orifice transluminal endoscopic surgery in urology: a critical analysis of the literature. Eur Urol 59:26–45 15. Cindolo L, Gidaro S, Tamburro FR, Schips L (2010) Laparoendoscopic single-site left transperitoneal adrenalectomy. Eur Urol 57(5):911–914 16. Autorino R, Kaouk JH, Stolzenburg JU et al (2012) Current status and future directions of robotic single-site surgery: a systematic review. Eur Urol 63(2):266–280 17. Horise Y, Nishikawa A, Sekimoto M et al (2012) Development and evaluation of a master-slave robot system for single-incision
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laparoscopic surgery. Int J Comput Assist Radiol Surg 7(2):289–296 Shin W, Kwon D (2013) Surgical robot system for single-port surgery with novel joint mechanism. IEEE Trans Biomed Eng 60(4):937–944 Haber GP, Autorino R, Laydner H et al (2012) SPIDER surgical system for urologic procedures with laparoendoscopic single-site surgery: from initial laboratory experience to first clinical application. Eur Urol 61(2):415–422 Xu K, Goldman RE, Ding J, Allen PK, Fowler DL, Simaa N (2009) System design of an insertable robotic effector platform for single port access (SPA) surgery. In: Intelligent robots and systems, pp. 5546–5552 Piccigallo M, Scarfogliero U, Quaglia C, Petroni G, Valdastri P, Menciassi A, Dario P (2010) Design of a novel bimanual robotic system for single-port laparoscopy. IEEE/ASME Trans Mechatron 15(6):871–878 Lee H, Choi Y, Yi B-J (2012) Stackable 4-BAR manipulators for single port access surgery. IEEE/ASME Trans Mechatron 17(1):157–166 Kobayashi Y, Tomono Y, Sekiguchi Y et al (2010) A surgical robot with vision field control for single port endoscopic surgery. Int J Med Robot Comput Assist Surg 6(4):454–464
24. Sekiguchi Y, Kobayashi Y, Watanabe H et al (2011) ‘‘In vivo experiments of a surgical robot with vision field control for single port endoscopic surgery,’’ Engineering in Medicine and Biology Society. In: Annual international conference of the IEEE, pp. 7045–7048 25. Richards C, Rosen J, Hannaford B, Pellegrini C, Sinanan M (2000) Skills evaluation in minimally invasive surgery using force/torque signatures. Surg Endosc 14:791–798 26. Lazeroms M, Villavicencio G, Jongkind W, Honderd G (1996) ‘‘Optical fibre force sensor for minimal-invasive-surgery grasping instruments,’’ Engineering in Medicine and Biology Society, Bridging Disciplines for Biomedicine. In: Proceedings of the 18th annual international conference of the IEEE, vol 1, pp. 234–235 27. www.intuitivesurgical.com. Accessed 25 Jun 2013 28. Cheon B, Gezgin E, Ji DK, Tomikawa M, Hashizume M, Hong J (2013) Design of a novel single incision laparoscopic surgery robot with increased tissue handling force. In: Proceeding of CARS 2013
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and Other Interventional Techniques
A single port laparoscopic surgery robot with high force transmission and a large workspace Byungsik Cheon • Erkin Gezgin • Dae Keun Ji Morimasa Tomikawa • Makoto Hashizume • Hong-Jin Kim • Jaesung Hong
•
Received: 21 August 2013 / Accepted: 31 March 2014 Ó Springer Science+Business Media New York 2014
Abstract Introduction This study presents the design of a novel single port laparoscopic surgery robot that is actuated by plate-spring-driven mechanisms with high force transmission and a larger workspace. Many ongoing studies aim to develop robotic single port laparoscopic surgery platforms due to the potential advantages in terms of a short recovery period and fewer postoperative scars. Most of these investigations of single port access have focused on resolving the inconvenient maneuverability of manual single port laparoscopic surgery. However, drive mechanism structures are another requirement. Materials and Methods Most of the existing robotic platforms cannot transmit sufficient force, as many of them use wire-driven mechanisms, which are prone to mechanical deformation that also negatively affects the accuracy of the end effector. In addition, even the best-known
laparoscopic surgical robot system has instruments with a limited workspace for single port laparoscopic surgery. Therefore, the purpose of this study was to propose a novel robotic single port laparoscopic surgery platform that uses plate springs to transmit higher forces during tissue handling. Results and Conclusion Compared to wire- or link-driven mechanisms, the plate-spring mechanism provided surpassing force transmission, with [14 N force transmission achieved, which enables most laparoscopic surgery with single port access. In addition, the high degree of freedom structure of the proposed design permitted an expanded workspace, which might be the most competitive characteristic among the single port systems reported to date.
Electronic supplementary material The online version of this article (doi:10.1007/s00464-014-3534-6) contains supplementary material, which is available to authorized users.
Laparoscopic surgery is one of the most successful medical applications that have emerged since the end of the last century. By opening tiny incisions on the abdominal surface, laparoscopic surgery allows surgeons to operate inside the body using specialized laparoscopic instruments. Operations result in less blood loss, reduced postoperative scaring, fewer complications, and faster recovery compared with those of standard open surgery [1]. As the potential of methods has been realized through their successful implementation, continuous efforts have been made to reduce the number of incisions needed. Consequently, natural orifice transluminal endoscopic surgery (NOTES) and single port laparoscopic surgery (SPLS) have been proposed. Although these methods have similarities, such as their minimal invasiveness, NOTES uses a natural orifice entry and an incision inside the body,
B. Cheon E. Gezgin D. K. Ji J. Hong (&) Department of Robotics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Korea e-mail: [email protected] E. Gezgin Department of Mechatronics Engineering, Izmir Katip Celebi University, Izmir, Turkey M. Tomikawa M. Hashizume Department of Advanced Medical Initiatives, Faculty of Medical Sciences, Kyushu University, Fukuoka, Japan H.-J. Kim Department of HBP Surgery, Yeungnam University Hospital, Daegu, Korea
Keywords Single port laparoscopic surgery Plate spring Robotic surgery
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whereas SPLS uses a single incision on the abdominal surface, preferably the navel. However, several problems remain unsolved, and difficulties have been reported in clinical NOTES trials [2–4]. As a result, SPLS procedures are increasing in both popularity and feasibility, and are considered a possible alternative to conventional laparoscopic surgery [5, 6]. The merits of multi-port and single port surgery are debated. As Marks et al. [7] reported, the advantages of single port surgery have not been demonstrated sufficiently in terms of blood loss, complications, or pain scores. It also requires longer operating times, although the cosmetic score is higher. Therefore, careful consideration is required when choosing single port laparoscopic surgery instead of multiport access. The proposed robot might contribute when the single port access procedures are selected. If the issues of single port laparoscopic surgery are overcome by the development of new instruments, such as the proposed system, the number of such surgeries will increase. The first single port laparoscopic surgery was reported in 1998 by Esposito [8]. Since that trial, novel instruments and specialized techniques have been developed to overcome the technical limitations due to its use of traditional laparoscopic instruments in a single incision [9, 10]. Thanks to these developments and much scientific research, many clinical operations can be carried out with a single incision, such as cholecystectomy, appendectomy, hysterectomy, tubal ligation, ovarian cystectomy, nephrectomy, partial nephrectomy [11], ureterolithotomy [12], and prostatectomy. Nevertheless, surgeons remain reluctant to perform single port laparoscopic surgery, as technical challenges remain. The most typical of these, counter-intuitive usage, in which the procedure is conducted using crossed laparoscopic instruments to increase operative workspace, confuses the sense of right–left direction. Long periods of intense concentration are required during operations to prevent physical contact between the laparoscopic instruments [13–15]. In addition, the surgeon’s visibility is likely to be limited, as laparoscopes and other medical instruments are aligned in the same direction [1]. Due to this problem, surgeons have difficulty securing a sufficiently clear view to manipulate surgical instruments. The use of robots as an alternative approach to overcome these problems is becoming more popular. Using master and slave systems makes it easy to overcome counter-intuitive usage and conduct precise operations. Moreover, it is possible to use enhanced vision systems to eliminate visibility issues. In contrast, as a robot manipulator must enter the body from a single port, its size, transmission, and parallel orientation to the workspace are becoming serious constraints.
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In response to these limitations, two major configurations have been proposed: the ‘‘X type’’ and ‘‘Y type.’’ Type X SPLS robots use a standard manual entry configuration, in which instruments controlled by individual serial robot manipulators enter the body from a single incision. Although the counter-intuitive operation problem is solved by means of master–slave control [16], and force transmission is sufficient, these robots have drawbacks including external arm collisions, large size, and relatively large incision size requirements. A SPLS robot designed by Horise et al. [17] is an example of the X-type robots under development. Type Y SPLS robots have two states. They enter the body in an ‘‘I’’ configuration from a single incision; once inside the body, they transform into a ‘‘Y’’ shape by opening two existing arms [18]. This procedure prevents possible arm collisions during operations, expands the effective workspace, and reduces the overall size, including the incision diameter. Despite its manual passive controls, the SPIDER system is the most similar to a SPLS robot, and represents the transition between a passive device and a robotic system for SPLS. It has been used clinically after gaining FDA approval [19]. As the SPIDER system uses wires for forceps manipulation, it is difficult to handle heavier payloads, so it is more appropriate for a limited range of operations, such as gastric band and gastric sleeve surgery. IREP, another snake-like robot with a 14 degree of freedom continuum, was developed for SPLS [20]. IREP is one of the smallest SPLS robots available and has advanced motion dexterity. However, it also has limits in terms of conducting general surgical operations with a large payload capacity. SPRINT, developed by Piccigallo et al. [21], has one of the highest force transmission capabilities among its rivals. This robot has six degrees of freedom in its single arm, and on-board motors and gear boxes within its arm segments, yet a larger incision diameter is required due to the size of the arms. Other examples include stackable four-bar manipulators [22], and a design using flexible shafts in its motion transmission that transmits substantial force values without using wires [23, 24]. However, both have limited manipulation capabilities. Considering all of the strengths and weaknesses of the previous studies, we propose a novel Y-type robotic SPLS platform design that transmits relatively higher force during tissue handling by incorporating plate springs in the structure. In addition, the high degree of freedom design structure permits an expanded workspace, which enables operations across a wide surgical area without changing the system setup.
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Fig. 1 Plate spring under compression with and without guides. The plate spring with appropriate guides can deliver a compressive force that is cannot be realized by wires
Design
Fig. 2 Differences in the assemblies of wires and a plate spring: dual and single assembly
We set the design specifications in terms of size, force transmission, and robot structure. Thus, it is important to clarify the main constraints and goals of the design. The stem must adhere to a diameter \25 mm to avoid scar formation and reduce wound pain. The second constraint is a result of the force requirements of surgical procedures. According to Richards et al. [25] and Lazeroms et al. [26], a force range of ±10 N on the forceps tool tip is appropriate. Last, a dual-arm Y-type robot manipulator structure was to have six degrees of freedom in each arm to expand the workspace and avoid collisions. Plate-spring-driven structure As mentioned previously, the greatest problem with SPLS robots is their size limitation, which creates difficulties with force transmission between the actuators and forceps. The trade-off between the volume of the transmission structures and their force transmission capabilities requires an optimal design solution. In contrast to the bulkiness of gearboxes and the weaknesses of wired systems, plate springs have the optimum specifications in terms of design constraints. Similar to wires, they can transmit tension from the actuators and the end effector. However, they have the unique property of being able to deliver compressive forces provided that they are assembled inside the guides (Fig. 1). As a result, a single force for pull or push is sufficient, whereas two pulling forces are required for motion using a wire-driven mechanism (Fig. 2). In addition, having a larger crosssectional area provides relatively greater force transmission compared with those of wires. Besides, its compact size greatly reduces the volume occupied by the transmission mechanism, contrary to gearboxes or links. Notably, the
Fig. 3 Plate springs: assembly on the dual arms of the first prototype mechanism
large surface-contact area between the plate spring and the guide increases friction. As a result, lubrication or lowresistance materials should be used inside the guides. The actual assembly of the plate springs can be seen in the first prototype mechanism shown in Fig. 3. The platespring mechanism was applied for joint 3, the joint used most frequently, and the one requiring greater force. Workspace and degree of freedom considerations Generally, type Y SPLS robots are incapable of operating on relatively large organs, such as the liver and intestines, because of the fixed starting point of the two arms, where they open to expand the workspace. Unlike the type X robots, this disadvantage prevents creation of a long stroke between the ends of laparoscopic forceps. To overcome this constraint, a long stroke is ensured by separating the starting point by two individual prismatic joints for each arm. Additionally, this added degree of freedom provides a
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Surg Endosc Fig. 4 Comparison of workspace configurations and possible postures: X type, Y type, and modified Y type SPLS robots with additional prismatic joints
Fig. 5 Three-dimensional model of an average size, 3,000 cm3 CO2insufflated human body
SPLS robots. A total of 12 degrees of freedom is achieved after adding the overall mobility of the two individual arms. After the structural synthesis and prior to deciding the robot manipulator construction parameters, the average size of the human body was modeled using three-dimensional (3D) modeling software and taking into consideration the classical SPLS, in which approximately 3,000 cm3 CO2 is insufflated into the abdominal cavity (Fig. 5). A coarse robot manipulator model was assembled in a virtual environment after constructing a soft working environment (Fig. 6), and pre-construction parameters were controlled so they could be refined after the kinematic analysis. Mechanical implementation
Fig. 6 Three-dimensional model of the coarse manipulator and virtual working environment
larger, more efficient workspace with increased postural possibilities for the forceps (Fig. 4). The remaining mobility of the robot manipulator is determined by preserving the four degrees of freedom of classical laparoscopy and the one native degree of freedom to open the arms from the classical configuration of type Y
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A final prototype-ready model was prepared using 3D modeling software following the workspace analysis and determination of the construction parameters. The proposed robot was named ‘‘PLAS,’’ which stands for PLAteSpring mechanism-based LAparoscopic Surgery robot. As seen in Fig. 7, PLAS is composed of two main sections. The first section includes the robotic arms that will conduct the surgical operations and the stem of the robot that will enter the human body from a single incision. The second, actuation, section includes all of the distinct actuators that will confer 12 degrees of freedom. The actuation section of the robot always remains outside of the body. The main stem is designed to be cylindrical to preserve existing trocar compatibility. Trocars are the introducers that enable subsequent placement of surgical instruments
Surg Endosc Fig. 7 Structure of the proposed single port laparoscopic surgery (SPLS) robot: PLAS
motion of the fourth revolute joint is actuated using wires. The motions of the left arm and their responsible actuators are shown in Fig. 10. After completing the 3D modeling, a final PLAS prototype was manufactured and assembled (Fig. 11) for use in laboratory and animal experiments.
Fig. 8 Cross section view of PLAS
Fig. 9 Left arm configuration of PLAS. Right arm has an identical structure
without a CO2 leak. The stem of the manipulator holds the passages for laparoscopes, forceps, plate springs, wires, and the robotic arms (Fig. 8). Each arm of PLAS has six degrees of freedom, including two prismatic and four revolute pairs (Fig. 9). The grasping motion of the end effector is excluded from the degrees of freedom calculation, and the out-of-plane
Potential surgical task The PLAS robot can be used to perform various surgical tasks required for general laparoscopic surgery. These tasks include lifting the liver, holding tissue, cutting tissue, etc. It has been difficult to perform laparoscopic surgery via a single port because the instruments for SPLS do not have sufficient workspace or exert sufficient force to handle the tissue [19]. Accordingly, an operation must be performed in a restricted area, and the setup must be repeated when the surgical site is moved during the surgery [27]. In addition, the size and weight of tissue that can be held are limited owing to the insufficient force of the instrument. The PLAS robot has advantages in terms of the force and task area. It covers a larger workspace than the da Vinci system [27] and enables greater force than the SPIDER system [19]. If a single port laparoscopic surgery robot can guarantee sufficient force and task area, most laparoscopic surgery could be replaced by single port laparoscopic surgery. Figure 12 shows the basic configuration of a surgical task for partial hepatectomy with PLAS. PLAS has a hole for inserting a flexible endoscope, but does not have an additional supporting structure to hold the endoscope. A tool change is also impossible with the current version of PLAS. Therefore, several ports and forceps might be
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Fig. 11 Final prototype of PLAS
Fig. 12 A possible setup of PLAS for partial hepatectomy
Fig. 10 Various joints and corresponding motions of the left arm
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required to perform an entire procedure, such as a laparoscopic hepatectomy. PLAS can hold and move tissue ranging in size from a small piece to the entire right or left lobe of the liver. If another instrument were available, it could be used for coagulation, clipping, or other operations, while PLAS is
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Fig. 13 The large task area of PLAS for liver resection
holding the liver tissue. Alternatively, if another forceps can hold the liver and make sufficient task space, PLAS can be used for cutting and clipping the tissue or blood vessels. When using extra instruments, PLAS functions more efficiently than other instruments, so that the number of necessary incisions is reduced to a minimum. The current version of PLAS has two types of instrument installed: for grasping and cutting. The next version of PLAS might include an automatic or semi-automatic tool change function, as well as an endoscope-holding structure distally. PLAS can be used most efficiently for laparoscopic surgery requiring a large workspace, such as for laparoscopic hepatectomy. A cholecystectomy or appendectomy can be performed relatively easily by other single port surgery robots, such as the da Vinci and SPIDER systems. We developed PLAS with the goal of performing more difficult surgeries, such as laparoscopic hepatectomy. Figure 13 shows the workspace of PLAS for liver resection. The prismatic joint allows the arms of PLAS to be spread wide, and maintains the distance between the arms. This allows PLAS to cut a large area of liver tissue without changing the robot pose or setup. No other commercial system covers as large an area.
Table 1 Force transmission experiment setup details Joint i
PLAS arm posture
Force gage tip distance (mm)
1
Straight
–
2
Angled
60
3
Angled
15
4
Angled
15
5
Straight
–
6
Angled
20
Grasping
Straight
15
Fig. 14 Force transmission measured at each joint using a force gage
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Surg Endosc Fig. 15 Experimental setup for measurement of position repeatability with various payloads
Experiments and results After assembling the PLAS, a series of laboratory and field experiments were carried out to verify the force transmission capabilities of the joints and end-effector position repeatability. The first laboratory test was conducted using a force gage that was fixed firmly onto a vibration-free table using the magnetic base. Measurements were taken from each of the joints, which were actuated individually during five trials. The details of the experimental setup including the force gage tip distance measured from the rotation axis of the related joints and the posture of the PLAS arm are shown in Table 1. The results for each configuration are shown in Fig. 14. Because the left arm has the same structure and performance as the right arm, only the right arm of PLAS was used in the trials. The second laboratory test was conducted using the PolarisÒ optical tracking system which is a product of NDI (Canada, Ontario, Waterloo). End-effector positions were tracked by PolarisÒ under the actuation of joint 3 to evaluate the repeatability of the end-effector positions and the reliability of the plate-spring drive under predefined loads. Infrared reflectors were attached to the end effector to provide a position tracking reference, and a weight
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counterbalance with a pulley was used to simulate payload (Fig. 15). We determined a fixed trajectory to evaluate available payload. Eight experiments were conducted under loading conditions with 200, 400, 600, 800, 1,200, and 1,600-g weights, in addition to an experiment with no payload. Each loading condition was subjected to five trials and the results were collated (Fig. 16). The PLAS trajectory remained constant until 1,400 g, but a normal PLAS trajectory was not obtained at 1,600 g. After the laboratory test trials, an animal experiment was conducted using animal subjects and living tissues with the permission of the animal experiment review committee of Kyushu University and under the supervision of expert surgeons (Fig. 17). The surgeon performed a liver dissection using PLAS and determined that it has sufficient force transmission capability to handle the organs during surgery.
Discussion The first PLAS prototype outperformed its rivals. The results were promising in terms of force transmission capabilities and workspace availability.
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Fig. 17 Animal experiments under the supervision of expert surgeons. Cutting of liver tissue was performed in a pig
Fig. 16 Trajectories moved with various payloads
The force gage experiments revealed that PLAS had margins sufficient to achieve the 10-N goal at the forceps, even with single contributions from all joints, with the
exception of joint 4. For example, readings taken 15 mm away during the plate-spring trial actuating joint 3 (Fig. 16) showed that to achieve the force transmission goal of 10 N at the forceps using only joint 3, summation of the variable parameter d5 and design parameter d6 (Fig. 7) should not exceed 50 mm; this was readily achievable using the control algorithm. If larger workspaces and higher forces are required, the required force can be supplied by other actuators. The wire-driven and off-plane structures of PLAS joint 4 result in the weakest force transmission capability, and it should be refined using either another spring drive or an alternative mechanism in future prototypes. Evaluation of the reliability and repeatability of the proposed plate-spring actuation under various loading conditions showed that the paths of the forceps remained uniform even at higher loadings up to 1,400 g.
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These results suggest that the plate-spring drive is a promising alternative for SPLS robot design. Furthermore, field experiments on animal subjects and living tissues demonstrated that PLAS reaction speeds, force transmission capabilities, maneuverability, and workspace configurations are suitable. In an animal experiment, the force used to handle tissue was appropriate. It was sufficient to handle the entire liver or just a small tissue segment during the surgery. Despite the considerable force used, no tissue damage occurred. The robot has a stronger force than other single port robots, but does not exceed that of multi-port robots, such as da Vinci system. Therefore, it is considered to be at least as safe as da Vinci system. The robot does not have haptic function. This might cause some problems, as with da Vinci. Many surgeons believe that tissue damage can be avoided by making use of the visual information in the endoscopic image. Haptic function might be dealt with as a separate topic in future research. The structure of the PLAS prototype should also be mentioned with respect to the predefined goals. The Y-shaped configuration of PLAS resolved the problem of counter-intuitive operation of single port laparoscopic surgeries, and adding prismatic joint 1 to the structure solved the workspace weaknesses of Y-type structures. We constructed the prototype from aluminum, rather than originally planned stainless steel, to make its manufacture easier and cheaper [28]. Thus, the diameter of the main stem had to be increased to 33 mm to meet the stiffness requirement. Although this value was lower than those of other SPLS robots [21], exchanging aluminum for a stiffer material in future prototypes will facilitate manufacture of instruments with main stem diameters \25 mm.
Conclusions In conclusion, we constructed a novel single port surgical robot named PLAS that achieved the desired increase in force transmission capability and workspace volume by utilizing a novel plate-spring-driven design. The results of both laboratory and animal experiments were promising and will be enhanced further in future prototypes. Although additional functions, such as a laparoscope holder, and various instruments are required for clinical use, PLAS provides a possibility for increasing the use of single port laparoscopic surgery. Acknowledgments We appreciate the advice from the Prof. WooJung Lee at Yonsei University, and we appreciate the helpful comment and idea by Prof. Takeshi Ohdaira at Kyushu University. We also appreciate the help for paper organization by Prof. Pyung Hun Chang at DGIST. Mr. Seongbo Shim who is a Master student at
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surgical robotics lab., DGIST also helped greatly for the revision of the paper. This work was supported in part by the DGIST MIREBraiN Program, the R&D Program of th DGIST Convergence Science Center (12-BD-0402), and the Health and Medical R&D Program of the Ministry of Health and Welfare of Korea (HI13C1634). Disclosures Mrs. Byungsik Cheon, Erkin Gezgin, Dae Keun Ji, Morimasa Tomikawa, Makoto Hashizume, Hong-Jin Kim, and Jaesung Hong have no conflicts of interest or financial ties to disclose.
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