Lessons learned using the insertable robotic effector platform (IREP) for single port access surgery
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- Simaan, N., Bajo, A., Reiter, A. et al. J Robotic Surg (2013) 7: 235. doi:10.1007/s11701-013-0400-9
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This paper presents the preliminary evaluation of a robotic system for single port access surgery. This system may be deployed through a 15-mm incision. It deploys two surgical arms and a third arm manipulating a stereo-vision module that tracks instrument location. The paper presents the design of the robot along with experiments demonstrating the capabilities of this robot. The evaluation includes use of tasks from fundamentals of laparoscopic surgery, evaluation of telemanipulation accuracy, knot tying, and vision tracking of tools.
KeywordsSingle port access surgeryMinimally invasive surgeryNatural orifice surgery
To enable SPAS, researchers investigated manual and robotic solutions. Examples of manual instruments include Realhand® from Novare, Cambridge Endo and EndoSAMURAI from Olympus Corp., or Spider from Transenterix. These instruments provide distal tool tip dexterity and can articulate to avoid collisions between the operator hands . Animal studies of single port access laparoscopic cholecystectomy have been reported using these instruments . However, the use of manual instruments presents ergonomic challenges, requires surgeons to operate using un-intuitive hand movements and relies on exceptional hand–eye coordination and substantial training. More importantly, manual instruments do not harness the full potential of computer-aided surgery. Manual instruments only augment the surgeon’s reach and dexterity. On the other hand, robotic systems are capable of augmenting sensory perception (e.g. by providing force sensing and feedback), interpretation of the surgical scene (e.g. by registering preoperative images to intraoperative secenes through the use of image overlay) and the accuracy and safety of surgical execution (e.g. by using active constraints or telemanipulation virtual fixtures).
For these reasons, researchers explored robotic assistance for SPAS and natural orifice transluminal endoscopic surgery (NOTES). Abbott  developed a wire-actuated dual-arm robotic system for NOTES which has 16 degrees of freedom (DoF) and a diameter (∅) larger than 20 mm. Kencana et al.  presented a 9 DoF ∅22 mm dual-arm robot. Lehman et al.  developed a NOTES robot that may be inserted into the abdomen via a ∅20 mm overtube and could be attached to the abdomen using external magnets. This design requires the surgeon to switch the device from a folded to a working configuration. Recently, Harada et al.  introduced a novel concept of a reconfigurable self-assembling robot for NOTES. This concept has yet to be experimentally proven. Lee et al.  presented a stackable four-bar mechanism for SPAS. Piccigallo et al.  presented a dual-arm robot for SPAS. This design embeds motors inside its surgical arms. Each arm is ∅23 mm and the requires access is ∅30 mm. Xu et al.  presented a concept for a trans-esophageal NOTES robot using design features of the IREP. Finally, Larkin et al.  presented a dual-arm SPAS system that uses wire-actuated snake-like articulated linkages. In contrast to this design, the IREP uses push–pull actuation and super-elastic NiTi backbones.
The IREP was designed by combining our past experience in designing systems for MIS of the throat  and for vision-guided automated surgical tool tracking . The initial design considerations of this system have been described in [11, 12].
The IREP, we believe, is currently the smallest robotic system for SPAS, requiring an access port of only ∅15 mm while offering dual-arm dexterous operation with sub-millimeter accuracy, 3D visualization, and automated instrument tracking. It has two ∅6.4 mm dexterous surgical arms and a third arm manipulating a stereo-vision module. Each surgical arm includes a parallel mechanism, a passively flexible stem, an actively controlled continuum snake-like arm, a rotational wrist and a gripper. The parallel mechanisms control the distance between the bases of each snake arm. The total number of actuated DoF of the IREP is 21. These include seven actuated DoF for each surgical arm, three DoF for deploying and controlling the pan/tilt of a vision module, two DoF for each gripper and two DoF for axial insertion of each dexterous arm.
The detailed kinematic modeling and design specifications of the IREP were presented in . These specifications included the coverage of a workspace of at least 50 mm in each Cartesian direction, roll of the gripper about its longitudinal axis to enable suturing in confined spaces, ability to triangulate both surgical arms, ability to apply a 2-N lateral force in correspondence with surgical tissue manipulation forces and suturing , and ±0.25 mm in positioning accuracy to allow micro-surgical interaction. The design avoids the use of serially connected motorized joints (such as in [15, 16]) in order to limit backlash and to enhance sterilizability. The IREP also provides a controllable distance between the bases of its dexterous surgical arms to increase kinematic dexterity and dual-arm triangulation. Ding et al.  showed these advantages compared to other designs using dexterous arms emanating from a single lumen (e.g. [17, 18]).
The IREP has also been designed as a modular platform for multi-modal use including energy and drug delivery and suction applications for SPAS and NOTES. This is achieved through the use of tubular access channels within each surgical arm. The flexible continuum arms can also be used as independent tools for NOTES by deploying them through an over-tube.
The following is a description of lessons learned during early evaluation experiments using the IREP.
Materials and methods
The IREP was tested in extreme conditions assuming that the only available gross movement of the device is along the trocar’s longitudinal axis. We did not use all the four DoF available to standard MIS instruments since we wanted to determine the IREP’s dexterity and workspace without reliance on these additional DoF. The peg transfer task consists of grasping a plastic ring with one hand, removing the ring from the peg, transferring the ring to the other hand, and then placing the ring on another peg without dropping the ring. The simple suture and intracorporeal knot module consists of placing a suture through a dot on a rubber drain followed by tying intracorporeally a surgeon’s knot and two square knots. Using these two modules, we could assess functionality of the robotic device under direct vision. If completed, we recorded the time to complete each module.
To evaluate telemanipulation accuracy and the effect of vision feedback using the IREP’s cameras on user performance, we used a position-symmetric telemanipulation algorithm as described in . A trained user was asked to move the robot’s gripper along the circumference of a ∅12 mm circle. A grid paper with 500 μm grid was used as a back-drop. A high-definition digital microscope was used to record a video of the robot movement and color-based image segmentation software was developed to locate the center of a printed red dot attached to the robot’s gripper. This setup was needed since the movement accuracy of the IREP was very close or beyond the accuracy of commercial vision trackers available at our laboratory. Twenty experiments were equally split using two visual feedback methods: (a) using a high-definition microscope, (b) using the IREP’s on-board cameras. We calculated the root mean square (RMS) and maximal tracking error and recorded competion times.
To demonstrate our tool tracking algorithm we overlaid the location of each gripper tracking box on the images of the vision module. We used vision tracking algorithms combining several different color and texture features in a probabilistic framework described in . The features work together to assist each other when some cues are stronger than others, and the appearance of the tool is learned on-line. In this way, the tracker only requires an initial position and bounding box dimension on the first frame of the video sequence, and the appearance of the tool is learned on-the-fly as new views are presented to the camera and various conditions of the environment are changing. We have demonstrated this work in real surgical scenarios  as well as with the IREP gripper in this paper.
Finally, we used a Simulab LC-10 cholecystectomy model. A surgeon telemanipulated one arm of the IREP to verify the extent of its reachable workspace. A sequence of experiment images was recorded.
Results and discussion
Figure 2 shows the results of the FLS experiment. The experiment validated that the grippers of the IREP were able to firmly hold the triangular objects, that the movement of the dexterous arms was sufficient to allow object transfer, and that each dexterous arm could cover the entire FLS peg board (64 × 103 mm). The experiment, however, did reveal that the telemanipulation code suffered from several flaws, including: (a) there was an unnecessarily high scaling ratio (5:1) between the master and slave, (b) coupling of motion between the master and slave was not direct, (c) rotation of the grippers about their axis slightly affected the gripper tip position, (d) although movement in the mid-range of the trocar’s longitudinal insertion axis was intuitive for both hands, at the extremes of the range of movement in this axis the movement generated by the Cartesian stage carrying the IREP could only be controlled by the right master. Flaws (a–b) have later been fixed during debugging phases of the telemanipulation code. Flaw (c) is related to calibration of the continuum robotic arms and the fact that we used a Phantom Omni as the master interface, which made it difficult for the surgeon to rotate his hand in space without inducing translations. We have since then implemented an orientation telemanipulation mode. Exact calibration of the dexterous surgical arms remains a minor issue to address since our experience has shown that telemanipulation under surgeon vision allows for intuitive compensation for system imperfections.
Results of the circle-following experiments
RMS error (mm)
Max. error (mm)
Average time (s)
We demonstrated that the IREP can complete object transfer, knot tying and automated vision tracking of its grippers. We also demonstrated that the workspace of a single arm of the IREP is suitable to cover the surgical field of cholecystectomy—even when the IREP is only mounted on an insertion slide and not all the traditional four DoF of MIS tools are used. This means that the IREP can be mounted on a simple support arm instead of a four-DoF robot. The evaluation also showed that the limited wrist roll complicated the passing of circular needles. We evaluated the actual roll range of the IREP and redesiged the wrist to provide at least one full turn. The telemanipulation experiments showed that the IREP is capable of sub-millimetric precision and that the 640 × 480-pixel cameras of the IREP degrade the user’s performance. We are working to incorporate higher resolution cameras. Evaluation of the IREP in the near future will include quantification of payload capabilities, telemanipulation latency, and evaluation on animals.
This work was supported by NIH Grant No. 7R21EB007779. A. Bajo and N. Simaan were also supported by NSF Career Grant No. IIS-1063750. The evaluation experiments were performed under a research agreement with Titan Medical Inc. Dennis Fowler serves as a consultant for Titan Medical Inc.
Conflict of interest