Proceedings of the 2003 IEEURSl Intl. Conference on Intelligent Robots and Systems Las Vegs, Nevada October 2003 '
LER: The Light Endoscope Robot P. Berkelman, E. Boidard, P. Cinquin, J. Troccaz TIMC-IMAG Laboratory Institut Albert Bonniot 38706 La Tronche, France
[email protected] Abstract LER is a compact surgical assistant mbot for posirioning of an endoscope and camera during minimally invasive surgery. In contrast to typical endoscope manipulators, LER is particularly compact and lighiweight at 625 g and I10 mm in diametel; so that it is simple to set up and use, occupies nopoor space, and does not limit access to the patient in any way. Our current prototype is filly sterilizeable by autoclave and is readyf o r clinical trials. a features a full motion range of 360" in mtation and inclination to IO" f m m the horizontalplane and is backdriveable for manual positioning. Actuation forces are limited for safety. LER may be held in place on the abdomen by adhesive strips or sutures, or anached to the sides of the table wi?h elastic stmps or clamps. We have implemented a variety of dixerent user commund interfaces f o r E R , including a miniature keypad, automatic optical instnunenf motion tracking, and voice command recognition. Experimental trajectory following results and performance parameters are given.
1 Introduction Minimally invasive laparoscopic surgical procedures offer considerable advantages over open surgery through minimization of the trauma and recovery time of the patient due to the small size of the incisions. Laparoscopic procedures require increased skill on the part of the surgeon, however, and an endoscope and camera are necessary to visualize the intemal tissues of the patient on a video Screen during the surgery. As a surgeon generally needs to operate instruments with both hands during a procedure, the endoscope shaft must be held in place and pointed towards the tips of the instruments by an assistant. This endoscope pointing task may be perfonued by a robot as it is simple and well-defined, yet fatiguing for a human assistant. We have developed a lapmscopic endoscope manipulator which is dramatically easier to set up and use and less costly than all currently available alteratives due to its simplicity and small size. Our lightweight endoscope robot LER is shown on a simulated abdomen in Figure 1.
0-7803-7860-1/03/$17.00 02003 IEEE
Figure 1: Prototype LER on Abdomen Simulator
2 Prior Development Several other endoscope manipulators have been developed, have undergone clinical validation studies, have obtained various regulatory approvals, and are commercially available. These robots consist of a floor-standing base and a serial or parallel linkage arm to bold the endoscope. Our endoscope robot development has been based on the different approach of a much smaller, lightweight robot placed directly on the abdomen ofthe patient and attached to the side of the operating table. Other endoscope robots which have been developed include [I, 2, 31. It is advantageous to design the robot kinematics to simplify rotations about a remote center of motion to be fixed at the endoscope incision 141. The EndoAssist[5]from Armstrong Healthcare and the AESOP[6,7]systems f?om Computer Motion, Inc. are two systems currently available on the market. Clinical evaluation studies [S, 9, 10, 51, primarily undertaken using the EndoAssist and AESOP systems, have been generally favorable, indicating that the impact of using a robotic assistant in laparoscopic surgery is not significant regarding the safety or efficacy of the procedure, the
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Figure 2: First and Second Prototypes endoscope image is more stable, and execution times may be reduced.
2.1 Our Previous Prototypes Our two previously developed compact endoscope manipulator prototypes are pictured in Figure 2. Both of these prototypes were actuated by cables in flexible sleeves attached IO a separate actuator enclosure. The earliest prototype [I 1J used McKibben artificial pneumatic muscles [I21 to drive the cables. Four cables between the base ring and the top of the trocar were actuated in parallel to point the endoscope and a fifth cable between the trocar and the camera end of the endoscope acts against a compression spring to control the insenion depth of the endoscope. In the second prototype [13], the McKibben artificial muscle actuators were replaced by motors and rack-andpinion drives which were easier to control, quicker, and more accurate and reliable. A mechanism with two intersecting joints provides the azimuth and inclination rotational degrees of freedom necessary to orient the endoscope, with each degree of freedom actuated by a cable wound around a pulley. The endoscope insertion was actuated by a cable acting against a spring on the endoscope shaft, as before. The second endoscope manipulator prototype was tested on a cadaver to verify ifs functionality and usability on the human body in a typical operating room configuration. Feedback comments from the attending surgeons led us to modify the design to increase the range of motion in inclmation, better accommodate differenttrocar configurations, and enable the robot to be detached from the trocar without removing the trocar from the patient. Although the actuation of the robot by cables through flexible sleeves enables reduction of the weight and size of the mechanism to be placed on the abdomen, the setup and operation of these cables were found to be very troublesome. Three of the five cables must be suspended from above the robot mechanism, which may block the line of sight between a surgeon and the camera monitor. The fric-
Figure 3: Newest Prolotype Design
tion resistance of the cable actuation heavily depends on the bending radius, wear, and cable tension. Generdly the cables must be retensioned after each use and replaced periodically to prevent breakage. Friction and stretching of the cables cause hysteresis in the actuation of the robot. In the cument prototype the nuisance of the cables and flexible sleeves between the actuators and the robot was eliminated by integrating sterilizable miniature brushless motors directly m the robot mechanism.
3 Current Prototype The schematic model of our latest prototype is shown in Figure 3. The robot is fully sterilizable; all the coinponents can withstand standard autoclave cycles. The robot base is wide enough to pass over any standard endoscope trocar and the robot may be removed w N e leaving the @ocarin the patient. The trocar clamp accommodates trocars up to 12 mm in diameter. To eliminate the Bowden cables and sleeves and remote actuation of the previous prototypes, powerful miniature brushless motors were directly integrated into the robot mechanism. Since we could not iind any commercially available autoclavable encoders, linear Hall effect sensors on the brushless motors provide angular position feedback to the controllers. Compact single-axis controllers' provide proportionalintegral (PI) control of the brushless motors with Hall effect sensor feedback. The motor controllers are opcrated in 'Faulhakr2036U024B KI 155 'Faulhakr MCBL 2805
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position control mode to accurately hold a desired position and switch to velocity control when motion commands are given. Input and control gains, minimum and maximum speeds, maximum currents, and other controller parameters are fully configurable and can be saved to the motor controller EEPROMs. The motion commands to the motor controllers are generated hy a compact single-board compnter3 with multiple analog and digital inputs and outputs. Use of the singlehoard computer eliminates the need for a PC interface to the motor controllers and considerably simplifies the setup and initialization of the robot. The power supply, singleboard computer, and motor controllers are all contained in a 340 x 150 x 100 mm enclosure, so that the entire robot system is easily portable. The endoscope robot may be attached to the patient and operating table by several different means, depending on the patients and procedures to be performed. For large patients in the supine position, the robot may be fastened directly to the abdomen with adhesive sheets andlor sutures on the stabilizing feet on the base ring. For added stahility, elastic straps may be used to attach the base ring to the sides of the operating table. For patients on their sides or when maximum stability is necessary, the base ring may he clamped to the side of the table hy an articulated arm.
4 Experiments and Performance Parameters The trajectory following accuracy of the endoscope robot was measured using an optical localizer4 and infrared LEDs fixed to the end of the endoscope. Constant velocity motion commands were given in both directions for each degree of freedom. The trajectory responses of the cabledriven prototype in Figure 4 show settling times on the order of one second, and the curved lines in the inclination and insertion results show variations in velocity. The responses of the prototype with integrated motors in Figure 5 show greatly reduced settling times and much NOE nearly constant velocities. The overall trajectory following performance of LER is more than adequate for endoscope camera displacement during minimally invasive surgery. Measured performance parameters and programmed controller parameters for the LER are given as follows: Mass: LER Endoscope and Camera Backdriveability: Torque Backdrive force on fully extended endoscope 3ZWorld BLZIW 4Active Polaris, " h e m Digital Inc.
625 g 300-500g typical
0.45 N-m 1.5 N
Dimensions: Height Diameter Motion range: Azimuth rotation Inclination Extension Maximum speed Azimuth rotation lnclination Extension Maximum torque limit: Maximum force on fully extended endoscope: Actuation hysteresis:
75 mm
110" 360' continuous to 80" from vertical I60 mm
20 degredsecond 20 degreedsecond 25 "/second 6 N-m
20 N 0.38"
5 Command Interface Options An effective user command interface for the light endoscope robot should enable the surgeon to reposition the endoscope without any assistance and without releasing either of the instruments held in each hand. As motion commands can be given in both directions for each of the three DOF of the device, the command interface must provide a minimum of six binary command inputs plus an emergency stop command. Variable speeds for coarse-fine positioning would require additional commands. We have aimed to provide a variety of different command interface methods for surgeons to select from according to their own requirements and preferences. The command interface options that have been considered for the LER up to the present are described in the following sections. The motor drives of the LER were selected to he fairly easily backdriveable so that the endoscope may be positioned by hand whenever the current to the motors is switched off. This feature simplifies the initial setup of the robot system when the initial endoscope incision is made. Manual positioning of the robot is direct, simple, and intuitive, and is the easiest means for initial positioning of the robot before other instruments are introduced into the abdomen and while the surgeon has at least one hand free.
5.1 Existing Interfaces As the bands of the surgeon are occupied during surgery, it is straightforward to consider using pedal controls to command the robot motion. The earliest AESOP endoscope robot models used a foot pedal command interface [6]. However, there are several drawbacks to using pedal controllers for this application. First, fine positioning using pedals is difficult while the surgeon is standing. Second, other pedals are typically already in use for electrocautery and suction or irrigation. Finally, the pedal system must provide at least six command inputs as described
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Fizurc 4: Rotation. inclination. and insertion traiectorv res p n s e s with cable-driven prototype I
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Figure 5: Rotation, inclination, and insertion trajectory responses with current LER prototype
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earlier, so the pedal system will tend to be large. awkward, and complex. The Medsys LapMan@laparoscope manipulator includes a remote wireless hand control unit which can be worn inside a glove to be operated by the middle, ring, and little fingers of the user. The FIPS Endoarm [I] uses a miniature finger-ring joystick attached to an instrument handle in the same position to be operated by the index finger. The Tongue Touch KeypadQfrom NewAbilities Systems, Inc. produces a wireless 9-button pressure-sensitive keypad to be wom in the upper palate of the mouth and operated by the tip of the tongue. It is used as a handsfree control interface for the disabled to control motorized wheelchairs and other electronic equipment and a p pliances. More recent models of the AESOP endoscope robot replace the pedal controller with a voice command system and clinical studies have been performed to compare the effectiveness of voice and pedal control 1141. Advances in voice recognition software technology and PC computational power have made a voice command interface fairly straigbtfonuard, although some training of both the system and the users is necessary for the best reliability. We have implemented a standard voice recognition system for the LER which has been found to perform well. Other systems have been developed to track motions of the surgeon’s head or eyes [15,161 to send commands to an endoscope robot. These command motions may be unnatural or awkward, however, and some time is necessary for the operator to become familiar with the system. A comparison with of face tracking with voice control for simulated laparoscopic tasks is given in [17]. Visual servoing to enable the robot to follow instrument tip motions automatically by analyzing the endo scope camera video images is an area of active research work [IS, 19,201. These methods involve marking the instrument tip with a distinctive color or pattern so that it is easily identified in the image. The problem is complicated by optical distortion, lighting variations, and partial occlusions of the instrument tip.
5.2 New Proposed Interfaces We have implemented a tracking system using an extemal optical localizer instead that does not depend on the endoscope camera image [XI. An e x t e d Optical localizer is used instead to detect the position of the robot base, the endoscope tip, and the tip of a selected instrument. The robot may then easily be commanded to align the endoscope to point to the instrument tip. A magnetic localizer could also be used instead, with the added advantage that occlusion of the position markers would not be a concern. We also use a miniature keypad which may be clipped onto the handle of any manual laparoscopic instmment
Figure 6: LER in Use on Cadaver next to the rotating wheel where it would be operated by the index finger of the user. This controller is not completely hands-free, but we observe that the index finger is generally free to move while a laparoscopic instrument is held in the hand, typically to rotate the tip of the instmment with a rotation wheel.
6 Testing The most recent LER bas also been tested on a cadaver during various dissection and training procedures (see video). The voice recognition command interface was used in combination with a pedal for safety and a miniature keypad attached to the instrument held in the right hand of the surgeon. The LER is shown in use and held in place on the abdomen by an articulated arm in Figure 6. At least three of the four attending surgeons rated all aspects of the LER as “good” or “excellent” except for the attachment betwteen the insertion acruation cable and the endoscope, which required detaching the light source cord in order to remove the actuation cable and the endoscope. Replacing the loop at the end of the actuation cable with a hook will eliminate this inconvenience.
7 Conclusion In summary, we have developed an endoscope manipulator with considerable advantages over current alternatives due to its compact size, light weight, ease of use, and low cost. Our final prototype is fully stedizable and ready for clinical uials once approval is granted by a review board, and have implemented several different user interfaces for hands-free control of the robot. When a LER is fixed to the table by a rigid articulated ann, it may used to manipulate laparoscopic insuuments as well as an endoscope. Furthermore, multiple LERs may be fixed to the table and placed on an abdomen at the same time to make up a complete teleoperated minimally invasive surgical robot system.
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Acknowledgements
1101 K. T. den Boer, M. Bruijn, I. E. Jaspers, L. I? S. Stassen, W. E M. van Erp, A. Jansen. I? M. N.Y. H. Go, I. Dankel-
The expertise and advice of Gildas de Saint Albin, JeanMarc Ayoubi, and Christian LBtoublon have greatly con-
man, and D. J. Gouma, ‘lime-action analysis of instrument positioners in lapamscopic cho1ecystectomy:’Surgical Endoscopy, vol. 16, pp. 142-147,2002. [ 111 P. 1. Berkelman, I? Cinquin, I. Troccaz, J. Ayoubi, C. Letoublon, and F. Bouchard, ‘A compact, compliant laparoscopic endoscope manipulator:’ in International Conference on Rob& and Auromtion, Washington D.C.),pp. 18701875, IEEE, May 2002. [I21 V. L. Nickel, M. D. I. Peny, and A. L. G m n , ‘Development of useful function in the severely paralyzed hand:’ loumal @”Bone andloinr Surgery, vol. 4SA, no. 5, pp. 933-
tributed to the success of this project. Alpes Instruments of Meylan, France, fabricated the device mechanism. Additional project support has been provided by F’raxim S.A., CNRS, and ANVAR through the MMM project.
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