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International Journal of ARM, VOL. 7, NO. 4, December 2006
Development of a 5-DOF Laparoscopic Assistant Robot Won-Ho Shin, Seong-Young Ko, Jonathan Kim, and Dong-Soo Kwon Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Republic of Korea (Tel : 82-42-869-3082; Fax : 82-42-869-3082 ; E-mail:
[email protected])
Abstract Laparoscopic surgery is a new surgery method that has many advantages including a short recovery time and fewer post-operative side effects. Although it has become increasingly popular, there remain problems in applying laparoscopic surgery. Many robotic systems were developed during the last decade to overcome these limitations. In this paper, a 5-DOF laparoscopic assistant robot system is proposed. It takes into account a number of requirements for assisting with laparoscopic surgery. The proposed system is expected to allow various laparoscopic surgeries to be performed with minimal interference with the surgeon. System analysis and experimental results of the system performance are presented.
1. INTRODUCTION Laparoscopic surgery, a type of minimally invasive surgery (MIS), is a new surgery method that has many advantages by reducing the size of the incision. Tissue damage is reduced, recovery time is shortened, and the post-operative effects of the surgery are decreased. Due to these advantages, many abdominal surgeries are performed with the laparoscopic technique. It is performed with several surgical tools and a laparoscope equipped with a CCD camera. As an assistant holds the laparoscope in the desired positions during the surgery, it is difficult to provide a stable view interminably due to hand tremors and fatigue. Moreover, the direction of the view and movement are reversed due to the fulcrum effect, and this often confuses the assistant. A number of robotic systems have been developed in the past several years to overcome these problems. In 1995, R. H. Taylor proposed a 7-DOF robotic system including a manipulator to carry the laparoscope or
other tools [1]. It creates a remote center of motion to operate the system with respect to the incision point. In 1995, J. Funda developed a 7-axis surgical robot (HISAR) for laparoscopic camera navigation that is mounted on the ceiling [2]. There are two robotic systems that are approved by the US Food and Drug Administration (FDA). The first of these is AESOP. Y. Wang initially developed this system with 4-DOF motion and a foot pedal control, and after going through several phases of improvement, the system’s dexterity was increased to 7-DOF motion with a voice-activated control [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. AESOP and EndoAssist were commercialized by Computer Motion and Armstrong Healthcare Limited, respectively. However, because these systems have a bulky base with wheels and arms, interference with the surgeon’s movement or with those of the assistants can occur during surgery. For this reason, a more miniaturized robot system is required. In 2002, P. Berkelman developed a compact robot system mounted on the patient’s abdomen [5]. Additionally, Y. J. Lee presented another type of laparoscopic assistant robot known as the KAIST Laparoscopic Assistant Robot (KaLAR) [6]. It has a bending mechanism with 2-DOF at the distal end and a linearly moving guide to enable zooming. It was specifically designed for laparoscopic cholecystectomy. In this paper, a 5-DOF laparoscopic assistant robot system is proposed that considers several system requirements. The proposed system is divided into three subsystems: a 3-DOF bendable laparoscope, a 2DOF external manipulator and a passive base. In these three subsystems, a 3-DOF bendable laparoscope is adopted from the original KaLAR system. For surgeries with relatively small surgical sites, such as cholecystectomy, only the original KaLAR system can be used. If the surgery requires movements outside the workspace of KaLAR, the entire 5-DOF system can be used.
Won-Ho Shin et al.: Development of a 5-DOF Laparoscopic Assistant Robot
The contents of the paper are organized in the following order: (1) system requirements, (2) system configuration, (3) system analysis, (4) experiments and (5) conclusion.
2. SYSTEM REQUIREMENTS The following section illustrates the factors that were considered in the design of the laparoscopic assistant robot. 2.1. Incision point constraint For practical use in a surgical environment, a laparoscope assistant robot has to satisfy the incision point constraint. When laparoscopic surgery is performed, the instrument and laparoscope pass through a small incision for entering the body. For the incision point constraint, the movement of the laparoscope requires 3-DOF during surgery, not including rotation, with respect to the long axis of the laparoscope. The 3-DOF motions are planar motion (left / right, up / down) and linear motion (zoom in / out) with respect to the incision point. This is shown in Fig. 1. The rotational motion with respect to the long axis of the laparoscope was discarded as its use was found to be minimal. With these 3-DOF motions, surgeons are able to access points within the abdominal cavity at any desired distance.
Fig. 1 3-DOF motion of the laparoscope
There are a number of ways to make a laparoscopic assistant robot such that the robot passes through a fixed incision point. These include: 1) a passive joint, 2) a remote center of motion, 3) a controlled redundant
system, or 4) an inner motion. The first option requires a 2-DOF passive joint to make a constrained motion. When the active arm operates a laparoscope around the patient’s abdomen, the laparoscope can move with respect to the incision point via the 2-DOF passive joint. In this case, the passive ones guarantee safety even if the patient moves during surgery. AESOP adopted a passive universal joint to operate the laparoscope [3]. The second option is for a system that always makes a remote center of motion with no other mechanism. If a remote center of motion coincides with the incision point, the system restricts the motion about the incision point. There are several mechanisms to create a remote center of motion, such as a double-parallelogram mechanism, a spherical joint mechanism, or an arc-motion guide mechanism. R. H. Taylor adopted a double-parallelogram mechanism and created a laparoscope maneuvering system [1]. The third option is to develop a system with redundant, actuated joints that are controlled about the incision point. To control this type of system, an accurate position control method is required. M. Michelin proposed a control scheme to manipulate an assistive robot system [12]. The fourth option is for a system that moves within the patient’s abdomen without external motions. Y. J. Lee adopted an internally bending mechanism in the development of a laparoscopic assistant robot [6]. In this paper, a laparoscopic assistant robot system that has a remote center of motion and an inner motion is proposed. 2.2. Workspace In laparoscopic surgery, the surgical workspace varies depending on such factors as the surgeon’s preferences, the conditions of the operating room, and the type of surgery. Moreover, it is not easy to measure the workspace during actual surgery due to safety and sterilization issues. Thus, it is difficult to define the required workspace of a laparoscopic assistant robot. J. Rosen measured the kinematics and dynamics of minimally invasive surgery tools during in vivo experiments with porcine models [7]. In his research, the position of surgical tools creates a circular cone with vertex angle of 60°. From this result, it can be assumed that the laparoscopic assistant robot should be able to provide a view with a similar range. 2.3. Safety and sterilization For robots with medical applications, safety and sterilization features are critical issues. Because surgical robots are directly in contact with the patient, improper control of the robot or a system malfunction may cause
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International Journal of ARM, VOL. 7, NO. 4, December 2006
catastrophic results. For this reason, several laparoscopic assistant robots have incorporated mechanisms or software architecture that can guarantee safety. In the proposed system, the bendable tip is flexible. If it collides with internal organs or tools, it bends immediately. The external manipulator’s motions are confined at to the incision point, and its mechanical parts are only in contact minimally with the patient. As the laparoscope is directly in contact with the human body, the inserted part of the laparoscope must have a waterproof design. For sterilization, the entire system should withstand the sterilization process. In addition, electrical parts such as motors and encoders should be kept away from the patient; they can be covered with drapes. Mechanical parts, such as links, should be detachable from electrical parts as well.
For application in general laparoscopy, a 2-DOF external manipulator was developed to extend the workspace of the original KaLAR system. This creates a remote center of motion on the patient’s abdomen wall. The combined motion of the original KaLAR system and the external manipulator can provide a wider view of the abdominal cavity. To create a remote center of motion, an arcguide mechanism was adopted. Fig. 3 shows the 2-DOF external manipulator components. To realize an arcguide mechanism for the system, a commercialized arc motion guide was used. An arc motion block is guided by an arc motion rail. In order to actuate the arc motion block, a wire driven system was adopted. The tilting of the arc guide is determined by a rotary axis driven by a geared motor. The remote center of motion is fixed by the center of the arc and the center of the rotating axis. As the arc guide mechanism has a simple structure, the surgeon can predict the movement intuitively.
3. SYSTEM CONFIGURATION With the aforementioned system requirements, a prototype of the laparoscopic assistant robot system was designed. A remote center of motion and an inner motion was used to control the laparoscope. With these two motions, the system can satisfy the requirements while minimizing interference with the surgeon. By adopting an inner motion, interference can be reduced by allowing external movements only when necessary. The new system is a 5-DOF assistant robot with three components: a 3-DOF bendable laparoscope, a 2-DOF external manipulator and a passive base. The 3-DOF bendable laparoscope was adopted from the original KaLAR system [6] for an inner motion. The inner motion generator is composed of a 2-DOF bending section actuated by a wire-driven mechanism and a 1DOF linear motion part using a linear guide, as shown in Fig. 2. The original KaLAR system was intended for application in laparoscopic surgery with a relatively small surgical site.
Fig. 2 3-DOF motion component from the KaLAR system
Fig. 3 2-DOF external manipulator component
To install the entire system on to a bed, a device compatible to the current surgical environment is needed. A commercialized passive holder with an additional link was used, as shown in Fig. 4. The additional link was used to determine the remote center of motion, which is the incision point during the initial installation procedure.
Fig. 4 Additional link with a passive base
Won-Ho Shin et al.: Development of a 5-DOF Laparoscopic Assistant Robot
Once the desirable position of the additional link is obtained, the passive base can be fixed to the operating table with a clamp. After fixation, the additional link is removed and the 2-DOF external manipulator is attached to the passive base. Finally, a 3-DOF bendable laparoscope is attached to the external manipulator by means of a connector. The connector facilitates a simple dismounting of the 3-DOF portion when the lens of the laparoscope has to be cleaned. Fig. 5 shows the assembly of the entire system.
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4.2. Forward kinematics The robot system consists of six frames, including the base frame, as shown in Fig. 6. Frame 1 is used to describe the amount of rotation along the arc guide with respect to base frame 0, while frame 2 is used to describe the amount of tilting of the arc guide. As the motion of a rotation axis and an arc guide creates a fixed point, the origins of frames 0, 1, and 2 are collocated at a point. This point is defined as the center of the arc and must lie on the rotating axis of the motor. Frame 3 describes the offset of the bending tip with respect to the base frame. The z-axis of frame 3 points along the laparoscope direction, and the x-axis points to a tangent line of the arc guide. Frames 4 and 5 are used to describe the 2DOF bending at the tip. The Denavit-Hartenberg (DH) parameters of the system are summarized in Table 2 [10]. The parameters are notated as follows: 1 2 3 4
d
Fig. 5 5-DOF laparoscopic assistant robot system
rotation angle along the arc guide tilting angle of the arc guide rotation angle about y3 ( up/down) rotation angle about x3 (left/right) distance from the trocar insertion point to the frames for internal bending
4. SYSTEM ANALYSIS 4.1. System parameters Table 1 shows the relevant parameters of the prototype system. Based on the system parameters and material properties, the center of mass and maximum moment of the system were calculated. The radius of the arc motion is determined by the specification of the commercial arc guide, while the motion range is determined by the geometric constrains of the assembled components. For the tilting of the arc guide, the maximum moment of the system is approximately 1.81Nm. For the rotation along the arc guide, maximum moment is approximately 0.06Nm. Table 1. Parameters of the prototype system Radius of the arc motion Base part size Laparoscope size Motion range
150 mm 102mm 105mm 62mm 450mm 53mm 48mm external L/R 80 , U/D 85 internal L/R 60 , U/D 60 120 mm translation
Fig. 6 Arc guide mechanism with reference frames
Table 2. Arc guide D-H parameters i
i-1
1
ai-1
di
i
0
0
0
1
2
2
0
0
2
3
2
0
d
0
4
2
0
0
0
0
5
2
3
2 4
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International Journal of ARM, VOL. 7, NO. 4, December 2006
Using the DH parameters defined in Table 2 and the transformation matrix, the forward kinematics can be solved using Eqs. (2.a)-(2.l) r11 r12 r13 px 0 3T
= 01T
1 2T
2 3T
3 4T
4 5T
=
r21 r22 r23 py r31 r32 r33 pz 0
0
0
1
(1)
r11 = (C1C2S3
C1S2C3)C4 + S1S4
(2.a)
r21 = (S1C2S3
S1S2C3)C4 C1S4
(2.b)
r31 = (S2S3
C2C3)C4
(2.c)
r12 = (C1C2S3
C1S2C3)S4 + S1C4
(2.d)
r22 = (S1C2S3
S1S2C3)S4 C1C4
(2.e)
r32 = (S2S3
C2C3)S4
(2.f)
r13 = C1C3C3
C1S2S3
(2.g)
r23 = S1C2C3
S1S2S3
(2.h)
r33 = S2C3
C2S3
Fig. 8 Workspace with only an external motion
(2.i)
px = C1S2d
(2.j)
py = S1S2d
(2.k)
pz = C2d
(2.l)
4.3. Workspace estimation Based on the system parameters and the forward kinematics, the motions of the 5-DOF system are simulated and the results are shown in Figs. 7, 8 and 9. The surfaces represent the positions of the tip; therefore, the actual viewable ranges are greater than they appear in the plot. The pivot or the incision point where the robot is inserted is marked by an asterisk.
Fig. 9 Workspace with a combined motion
Figs. 7, 8, and 9 show the workspace (units in millimeter) of the system with only a bending motion, an external motion, and a combined motion respectively. The internal bending angles varied from -30°~30°. The external angles varied from -40°~ 40°(tilting of the arc guide) and 30° ~ 115°(rotation along the arc guide). As shown in Fig. 7, the system with only bending motions cannot provide a sufficient workspace for complex surgery. Moreover, the viewable range heavily relies on the initial positioning of the robot. These problems can be solved by the combined motion with the external motion. As shown in Fig. 9, the combination of inner and external motions provides a more extensive workspace.
5. EXPERIMENTS Fig. 7 Workspace with only a bending motion
5.1. Interface and control As the surgeon’s hands are not free during surgery, a
Won-Ho Shin et al.: Development of a 5-DOF Laparoscopic Assistant Robot
hands-free command interface is preferred. Command interfaces that have been implemented for other laparoscope manipulators include voice [9], eye [8], foot pedal [9], head motion [4], and the autonomous tracking of the surgical tool [3]. In the proposed system, a voice-command interface was adopted. The user can command the robot system to operate with voice commands such as “up”, “down”, “left”, “right”, “zoom in” and “zoom out.” The voice command interface was implemented by adopting a voice module from Voiceware, Co. into the control program. In order to capture the surgical image data from a CCD camera in real time, a Meteor-II board from the Matrox Co. was used. To control the motors, a Sensoray 626 board was installed on the computer. Acquired image data are sent to the supervisory control system and to the monitor from which the surgeon obtains visual feedback. In laparoscopic surgery, the laparoscope has to have at least 3-DOF motion. The proposed system has 5DOF motion, and this requires a control scheme for the redundant degrees of freedom. To control the proposed system, a leader-follower scheme will be applied [11]. In this scheme, the 3-DOF bendable laparoscope is defined as the leader while the 2-DOF external manipulator is defined as the follower. When the system operates, the leader moves first until its maximum displacement is reached. The follower is then activated until the goal of obtaining a proper view is achieved. By using the leader-follower scheme, the interference with surgeon should be minimal due to the minimal movements of the external manipulator. 5.2. Experiments For a preliminary evaluation of the system performance, motion trajectories with a PD controller were presented for each joint. A voice command causes a step input, and this step input is converted to a ramp input in order to prevent a sudden and abrupt motion. A low-pass filter [j2]was also implemented for smoother motion. The experimental results of the 2-DOF external manipulator are shown in Fig. 10 to Fig. 13. The experiments with the 3-DOF bendable laparoscope were performed in the previous study [13]. Figs. 10 and 11 show rotation angle along the arc guide. Results of the tilting angle are shown in Figs. 12 and 13. As shown in these results, the error at each joint is less than 0.1 . The maximum error occurs at the instance where the input is given and gradually decreases as a function of time. The response of the system was determined as sufficient for an accurate positioning of the laparoscope.
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Fig. 10 Comparison of desired and actual trajectories along the arc guide
Fig. 11 Error during motion along the arc guide
Fig. 12 Comparison of desired and actual trajectories during the tilting of the arc guide
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International Journal of ARM, VOL. 7, NO. 4, December 2006
ACKNOWLEDGEMENTS This work was supported by the SRC/ERC program of MOST/KOSEF (Grant #R11-1999-008).
REFERENCES [1] R. H. Taylor et al., “A Telerobotic Assistant for Laparoscopic Surgery,” IEEE EMBS Magazine Special Issue on Robotics in Surgery, pp. 271-291, 1995. Fig. 13 Error during the tilting of the arc guide
6. CONCLUSION In this study, a 5-DOF laparoscopic assistant robot is proposed. The system consists of three main components: a 3-DOF bendable laparoscope, a 2-DOF external manipulator and a passive base. Using both external and internal motions, the system provides a sufficient workspace to perform general laparoscopic surgeries. In comparison with other systems, the proposed system involves less external motion due to the use of an internally bending mechanism. Thus, it is expected to lower the potential for interference with the surgeon or the patient. Moreover, the system can be mounted onto a bed and is compatible with existing surgical environments. A prototype of the system was developed taking into account the functional requirements for general laparoscopy. Based on the parameters of the prototype, a workspace analysis was performed. A control scheme to actuate the combined motion was presented. Image capturing and display capabilities were implemented using an image grabbing board, and a voice command interface was implemented by adopting commercial software into a control program. To confirm the performance of the proposed system, a series of motion control experiments was performed. From the experimental results, the system was determined to have sufficient response characteristics at each joint. However, a redundant control scheme for 5-DOF remains to be tested in order to demonstrate its effectiveness. Once the control issue is resolved, clinical experiments will be performed to verify the safety and adaptability of the system.
[2] J. Funda et al., “Control and Evaluation of a 7-axis Surgical Robot for Laparoscopy,” Proc. of the International Conf. on Robotics and Automation, pp. 1477-1484, 1995. [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 Applications 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 et al., “A Compact, Compliant Laparoscopic Endoscope Manipulator,” Proc. of the International 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] J. Rosen, et al., “The Blue DRAGON - A System for Measuring the Kinematics and the Dynamics of Minimally Invasive Surgical Tools In Vivo,” Proc. International Conference on Robotics & Automation, pp. 1876-1881, 2002. [8] Robert J. K. Jacob, “Eye-movement-based HumanComputer Interaction Technique: Toward NonCommand Interfaces”, Advances in Human-Computer Interaction, pp. 151-190, 1993. [9] 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.
Won-Ho Shin et al.: Development of a 5-DOF Laparoscopic Assistant Robot
[10] John J. Craig, Introduction to Robotics, 3rd ed. Pearson Education, Inc. 2005. [11] J. H. Hwang, “Coordinated Control of a Macro/Micro Robot,” KAIST, Master Thesis, 1999. [12] M. Michelin et al., “Dynamic Task Decoupling for Minimally Invasive Surgery Motions”, International Symposium on Experimental Robotics, 2004. [13] S. Y. Ko, J. Kim, W. J. Lee, D. S. Kwon, “A Compact Laparoscopic Assistant Robot using a Bending Mechanism”, Advanced Robotics, in press.
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