Design of a Dexterous and Compact Laparoscopic Assistant Robot

SICE-ICASE International Joint Conference 2006 Oct. 18-21, 2006 in Bexco, Busan, Korea

Design of a Dexterous and Compact Laparoscopic Assistant Robot Won-Ho Shin, Seong-Young Ko and Dong-Soo Kwon Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Korea (Tel : +82-42-869-3082; E-mail: [email protected])

Abstract: Laparoscopic surgery is a surgical approach that is performed with special surgical tools and a laparoscope. Due to its minimally invasive nature, there have been many attempts to improve its performance by applying robotics technology. In this paper, a 5-DOF laparoscopic assistant robot system with a bending mechanism is presented. A representative feature of this robotic system is that it has increased workspace to perform various laparoscopic surgeries. In addition, the proposed system can provide internal views with different perspectives. The system is expected to have sufficient safety features and an easy to sterilize mechanism for applications in various laparoscopic surgeries. Keywords: Laparoscopic Surgery, Surgical Assistant Robot, Surgical Robotics, Bending Mechanism they can interfere with the surgeon or with assistants during the surgery. For this reason, many research studies concerning a laparoscopic assistant robot system concentrate on a compact size and an easy setup. In 2002, P. Berkelman developed a compact robot system with rotation, inclination, and extension motions [5]. However, it occupies a large area of the patient’s abdomen for mounting and interference can occur during surgery. Yun-Ju Lee presented a laparoscopic assistant robot termed the KAIST Laparoscopic Assistant Robot (KaLAR) [6]. It has a bending mechanism to operate mainly within the patient’s abdomen and a zooming mechanism to enlarge the laparoscopic view. However, as it is designed for laparoscopic cholecystectomy, it is difficult to apply to general laparoscopic surgeries due its limited workspace. To allow for the application to general laparoscopy, a modified version of KaLAR is developed in this study. The proposed system is divided into three main subsystems: a passive base which holds the robotic system, an 2-DOF external manipulator, and a bending laparoscope. The bending laparoscope part provides 2-DOF bending motion and 1-DOF linear motion similar to KaLAR, and the external manipulator provides external motion with respect to the trocar insertion point. Therefore, the bending laparoscope combined with the external manipulator can provide sufficient workspace for the surgeon with a minimal amount of external motion. The following sections of this paper will present: 1) the system requirements, 2) the conceptual design, 3) the kinematical analysis of the system, 4) the control and interface and 5) the conclusion.

1. INTRODUCTION Currently, many abdominal surgeries are performed by the minimally invasive surgery (MIS). MIS can have great advantages by reducing incision area. Tissue damage is reduced, recovery time is shortened, and the aftereffects of the surgery are also decreased. In the past several decades, significant research efforts have been made in the development of technology for MIS, and more specifically in laparoscopic surgery [1]. Laparoscopic surgery, a type of MIS, is performed with several laparoscopic tools and with a laparoscope equipped with a CCD camera. As an assistant maneuvers the laparoscope following the surgeon’s commands, the assistant often has difficulty in holding the laparoscope for the duration of the procedure. Moreover, the direction of view and movement are reversed due to the fulcrum effect and this often confuses the assistant. To overcome these problems, a number of robotic systems have been developed during the last decade. In 1995, R. H. Taylor proposed a system including a manipulator to carry the laparoscope or other tools. His robot system is composed of a translation component (3-DOF), a remote center of motion component (2-DOF), and a distal component (2-DOF) [1]. It is operated by a small joystick mounted on the tool. J. Funda developed a ceiling-mounted seven-axis surgical robot (HISAR) for laparoscopic camera navigation in 1995 [2]. There are robotic systems that are approved by the US Food and Drug Administration (FDA). Y. Wang developed a 7-DOF AESOP system activated by a foot pedal and controlled by voice commands [3]. P.A. Finlay presented a robot system termed EndoAssist that operates with an angled laparoscope [4]. This system has a 3-DOF positioner that holds a 3-DOF arm to orient the camera. The above two systems were commercialized by Computer Motion and Armstrong Healthcare Limited, respectively. However, because these systems have bulky bodies with wheels and arms,

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2. SYSTEM REQUIREMENTS Laparoscopic surgery is performed in the abdominal cavity that is inflated by CO2 gas. The surgeon inserts surgical tools and a CCD camera, called a laparoscope, through incision points. During

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surgery, the surgeon watches the abdominal cavity with a monitor, and the camera operator maneuvers the laparoscope. When the laparoscope is stained with blood or smoke, the camera operator removes the laparoscope from the abdominal cavity and cleans the lens. Fig. 1 shows a typical operating room for laparoscopy surgery [7].

3. CONCEPTUAL DESIGN The entire system consists of three parts: a passive base, an external manipulator, a bending laparoscope. 3.1 Passive base The robot system has to be compatible with existing surgical environments. If additional devices are included with systems, laparoscopic assistant robot systems will generally require a lengthy set-up time. Therefore, commercialized medical passive holders that can be mounted easily on the operating table were used. Once a desirable orientation of the passive base is obtained, the base can be fixed to the operating table with a clamp. To setup the system at the proper position, an additional link is attached to the passive holder. The additional link is used to determine the remote center of motion, that is, the incision point during the initial installation procedure. 3.2 Bending laparoscope The bending laparoscope was retained from the original KaLAR system [6]. This part is composed of 2-DOF bending motion inside the patient’s abdomen and 1-DOF in-out motion outside the abdomen. The bending laparoscope is attached to the external manipulator, and its bending motion driven by a wire mechanism determines the internal angle of the laparoscope. A linear guide with a ball screw provides a zooming motion. Fig. 2 shows the KaLAR system with the passive holder.

Fig. 1 The laparoscopy operating room The following illustrates the factors that were considered in the design of the laparoscopic assistant robot. 2.1 Safety For special characteristics in medical applications, safety features are critical issues for medical robots. For industrial robots, the working space of the robot is separated from that of humans, but typically a medical robot operates close to both a patient and a surgeon. Furthermore, the surgeon does not have much knowledge of the robot, thus there is a danger of a malfunction or accidental misdirection. If a robot does not have safety features, it may hit the patient or a surgeon during surgery. For this reason, several laparoscopic assistant robots have incorporated mechanisms or software architecture that can guarantee safety. Safety features are realized by mechanically restricted motions with an arc guide mechanism. If there are incorrect commands from the surgeon, the restricted workspace of the system can reduce the potential for damage to tissues during surgery.

Fig. 2 KaLAR system with the passive holder

2.2 Sterilization As the laparoscope is directly in contact with the human body, sterilization problems should be considered during the designing phase. In particular, the part of the laparoscope that is inserted in the abdominal cavity has to be designed to be waterproof. For sterilization, the entire system should not include nonsterilizable components. In addition, electrical parts such as motors and encoders should be kept away from the patient, and can be covered with drapes. Mechanical parts, such as links, should be detachable from electrical parts.

3.3 External manipulator As mentioned in the introduction, the original KaLAR system has a limited amount of workspace. It can provide sufficient workspace for laparoscopic cholecystectomy, but it would be difficult to apply to other laparoscopic surgeries. The external manipulator was developed to extend the workspace of the original KaLAR system. The combined motion of the original KaLAR system and the external manipulator can provide a wide view of the abdominal cavity, allowing the system to be applied to general surgeries. Moreover it is possible for the surgeon to observe the side of the

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joints. Due to these advantages, the system with an arc guide mechanism does not have a large rigidity problem. Moreover, as it has a very simple structure, the surgeon can predict the movements of the system easily and thus, the interference with the system can be reduced.

organ. To move the laparoscope, the external manipulator has to have 2-DOF of motion. In addition, it has to create a fixed point via a mechanism or software. Fig. 3 shows several possible solutions that can provide 2-DOF.

Table 1. Evaluation of the mechanisms (a) (b) Easy Setup (+) 3 2 No Singularity (+) 1 3 Independency (+) 1 3 No External Force (+) 2 3 3 1 Redundant range of the motion (-) Number of joint (-) 2 2 3 2 Volume of the system (-) Gravity problem (-) 1 3 summation -2 3

(c) 2 1 1 3 1

(d) 2 3 3 3 1

1 2

1 2

2 1

3 4

3.4 Prototype of the system A prototype of the system is schematically shown in Fig. 4. To realize an arc guide mechanism for the system, a commercialized arc motion guide is used. An arc motion block is guided by an arc motion rail. It allows accurate arc motions in contrast to other arc mechanisms such as a cam-follower. In addition, it can be assembled easily with other parts with the use of bolts. In order to actuate the arc motion block, a wire driven system is adopted. The arc motion is driven by a geared motor attached at the arc motion block to provide the laparoscope its up/down motions. There is an assistive arc rail on which the wire is fastened, and it is bolted to the arc motion rail. The left/right motion of the laparoscope is determined by a rotary axis driven by a geared motor. The bending laparoscope is attached to the external manipulator with a connector. When the lens of the laparoscope has to be cleaned, the laparoscope can be easily taken out from the abdominal cavity during surgery.

Fig. 3 2-DOF Mechanisms The passive joint mechanism consists of the robot arm, the laparoscope, and the passive joint. The passive joint allows for compliance between the laparoscope and the incision point. Y.F. Wang and Hurteau R. adopted this mechanism to manipulate a laparoscope [3][9]. A double parallelogram mechanism produces a remote center of motion in a plane by combining two parallelogram linkages. R. H. Taylor and Y. Kobayahi adopted this mechanism to create a virtual fixed point that coincides with the incision point [1][8]. A spherical joint mechanism is the mechanism in which each axis of the joint intersects at a single point, which the links rotate on a sphere about a fixed point. N. Zemiti and Mitchell J.H. Lum adopted this mechanism to manipulate a laparoscopic tool [10][11]. An arc motion guide mechanism has one rotational axis and an arc motion guide component that can make an arc motion about a fixed point. M. Mitsuishi adopted this mechanism to manipulate a laparoscopic surgery system [12]. To choose the proper mechanism for the external manipulator of the present system, an evaluation of the mechanisms was performed. Table 1 shows the results of the evaluation. In the table, ‘Independency’ denotes whether or not the actuators were decoupled, and ‘No External Force’ is the magnitude of the external force at the abdominal wall. (+) indicates an advantage of the mechanism, and (-) indicates a disadvantage of the mechanism. Out of the many possible solutions, an arc guide was adopted as it allows the proper workspace with many advantages. Among these advantages are no singularity, no external force, independency, and a small number of

Fig. 4 Schematic of the system prototype

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is summarized in Table 3. The parameters are notated as follows: θ1 rotation angle from the vertical plane

Table 2 shows the relevant parameters of the prototype system.

θ2

Table 2. Parameters of the prototype system 150 mm Radius of the arc motion Base part size 102mm × 105mm × 62mm Laparoscope size 450mm × 53mm × 48mm Motion range external L/R 80° , U/D 85°

d l

arc motion angle from the horizontal plane distance between the incision point and laparoscope frame length of the laparoscope

Table 3. Arc guide D-H parameters i α a

internal L/R 60° , U/D 60°

1

120 mm translation

2

The size of the system is sufficiently small in order to reduce the potential for interference with the surgeon during surgery. However, the radius of the arc motion guide is the critical factor in determining the entire size of the system. If a smaller arc motion guide is adopted for the system, the size of the system can be reduced.

3

−

di

θi θ1 θ2

i −1

i −1

0

0

0

π

0

0

0

-d

0

0

l

0

2

π

2 4

For the transformation matrix, a generalized transformation matrix is defined as follows [15]:

4. KINEMATICAL ANALYSIS OF THE SYSTEM

− sinθi ai −1 cosθi 0 ⎡ ⎤ ⎢sinθ ∗ cosα ⎥ (1) ∗ − − ∗ θ α α α d cos cos sin sin i i i i i i i − 1 − 1 − 1 − 1 i −1 ⎢ ⎥ iT = ⎢sinθi ∗ sinαi−1 cosθi ∗ sinαi −1 cosαi−1 cosαi −1 ∗ di ⎥ ⎢ ⎥ 0 0 0 1 ⎣ ⎦

The robot system consists of a base frame, a rotation axis frame, an arc guide frame, a laparoscope frame, and an end-effector frame, as shown in Fig. 5. The numbering for the frames is Frame 0, 1, 2, 3, and 4. The origin of base Frame 0 is set at the incision point. As the motion of a rotation axis and an arc guide creates a fixed point, the origins of Frames 0, 1, and 2 are located in an identical point. Frame 2 is oriented such that the z-axis points along a perpendicular line about the plane of the arc guide. The z-axis of Frame 3 points along the laparoscope direction and x-axis points to a tangent line of the arc guide.

Using the DH parameters defined in Table 2 and the transformation matrix, forward kinematics Frame 0 to Frame 4 it the product of these transformation matrices.

T = 01T ∗12 T ∗23T ∗34 T

0 4

(2)

From these equations, the relative position and orientation of the end-effector is achieved. ⎡cosθ1 ∗ cosθ2 − sinθ1 cosθ1 ∗ sinθ2 cosθ1 ∗ sinθ2 ∗ (l − d)⎤ ⎢sinθ ∗ cosθ cosθ sinθ ∗ sinθ sinθ ∗ sinθ ∗ (l − d)⎥ (3) 2 1 1 2 1 2 ⎥ T =⎢ 1 ⎢ − sinθ2 0 cosθ2 cosθ2 ∗ (l − d) ⎥ ⎥ ⎢ 0 0 0 1 ⎦ ⎣

0 4

5. CONTROL AND INTERFACE The architecture of the system interface and control scheme is similar to original KaLAR system, as shown in Fig. 6. As the surgeon’s hands are not free during surgery, a hands-free command interface is required. Command interfaces that have been implemented for other laparoscope manipulators include voice [14], eye [13], foot pedal [14] and head motion [4]. In the original KaLAR system, voice commands such as “up”, ”down”, ”left”, ”right”, “zoom in” and “zoom out” are used [6]. However, there is the noise of the other medical devices in the operating room, thus voice recognition rates are often poor. To make continuous motion in the system, the surgeon often has to repeat the voice commands. To overcome this disadvantage, an auto-tracking method is used also in the original KaLAR system. Color tape was attached to each

Figure 5. Arc guide mechanism with coordinates

The Denavit-Hartenberg (DH) parameter of the system

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laparoscopic tool, and the system could recognize the tool position via image processing. When the system is in auto-tracking mode, the laparoscope continuously follows the laparoscopic tool. For a modified version of the original system, another interface such as head movements can be used to manipulate the system [4].

[3] Y. F. Wang, D. R. Uecker, and Y. Wang, “Choreographed scope maneuvering in robotically-assisted laparoscopy with active vision guidance,” Proc. 3rd IEEE Workshop on Application s of Computer Vision, pp.187-192, 1996. [4] P.A Finlay, “Clinical experience with a goniometric head-controlled laparoscope manipulator,” Proc. IARP Workshop on medical robotics, Vienna, 1996. [5] P. Berkelman, P. Cinquin, J. Troccaz, J.M. Ayoubi, C. Letoublon, and F. Bouchard, “A Compact, Compliant Laparoscopic Endoscope Manipulator,” Proc. of the Conf. on Robotics and Automation, pp 1870-1875, 2002. [6] Y. J. Lee, “Development of a Compact Laparoscopic Assistant Robot : KaLAR,” KAIST, Master Thesis, 2004. [7] B. V. MacFadyen and Jr. J. L. Ponsky, “Operative laparoscopy and Thoracoscopy”, Lippincott-Raven, Philadelphia, 1996. [8] Y. Kobayashi et al. “Small occupancy robotic mechanisms endoscopic surgery”, Medical Image Computing and Computer-Assisted Intervention, 2002. [9] Hurteau R, DeSantis S., Gegin E. And Gagner M., “laparoscopic Surgery Assisted by a Robotic Cameraman: Concept and Experimental Results”, IEEE International Conference on Robotics and Automation, pp 2286-2289,1994. [10] Nabil Zemiti, Tobias Ortmaier, and Guillaume Morel, “A New Robot for Force Control in Minimally Invasive Surgery”, IEEE International Conference on Intelligent Robots and Systems, pp 3643-3648, 2004 [11] Mitchell J.H.Lum, et al. “Multidisciplinary Approach for Developing a New Minimally Invasive Surgical Robotic System”, IEEE International Conference on Biomedical Robotics and Biomechatronics, pp 841-846, 2006 [12] M. Mitsuishi, et al., “Development of a Remote Minimally-Invasive Surgical System with Operational Environment Transmission capability”, IEEE International Conference on Robotics & Automation, pp2663-2670, 2003 [13] Jacob, R.J.K., “Eye-movement-based human-computer interaction technique: toward non-command interfaces”, Advances in Human-Computer Interaction, pp.151-190, 1993 [14] M.E. Allaf et al. “Laparoscopic visual field: voice vs. foot pedal interfaces for control of the Aesop robot”, Surgical Endoscopy, vol. 12, pp.1415-1418, 1998 [15] Craig. “Introduction to Robotics,” 3rd ed. Pearson Education, Inc. 2005

Fig. 6 Control and interface architecture In order to grab the surgical image data that is acquired from CCD camera in real-time, the Meteor-II board from the Matrox Co. is used. To control the motors, a Sensoray 626 board was installed on the computer. Acquired image data is sent to the supervisory control system and to the monitor system. In the auto-tracking mode, the supervisory control system uses the image data. In the voice command mode, the supervisory control system manipulates the system according to the surgeon’s commands.

6. CONCLUSION In this study, a laparoscopic assistant robot was proposed that can provide an extended view inside of the patient’s abdomen. The use of both external and internal motions is expected to provide sufficient workspace for performing general laparoscopic surgeries. In comparison with conventional systems such as AESOP, the proposed robot system is sufficiently compact to avoid interference with the movements of surgical staff during surgery. As the system can be mounted onto the bed, it is easy to setup and compatible with existing surgical environments. A prototype of the system proposed, but this does not guarantee that the system will operate well during actual surgery. Therefore, clinical experiments must be performed to verify the safety and adaptability of the system.

REFERENCES [1] R. H. Taylor, J. Funda, B. Eldridge, K. Gruben, D. LaRose, S. Gomory, M. Talamini, L. Kavoussi, and J. Anderson, “A telerobotic Assistant for Laparoscopic Surgery,” in IEEE EMBS Magazine Special Issue on Robotics in Surgery, pp. 271-291, 1995. [2] J. Funda et al. “Control and evaluation of a 7-axis surgical robot for laparoscopy,” Proc. Of the Conf. on Robotics and Automation, pp 1477-1484, 1995.

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