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Procedia CIRP 5 (2013) 133 - 136
The First CIRP Conference on Biomanufacturing
Force feedback manipulating system for neurosurgery
Yusuke KANADA, Takeshi YONEYAMA*, Tetsuyo WATANABE, Hiroyuki KAGAWA, Norifumi SUGIYAMA, Kazuya TANAKA, Takuya HANYU
Kanazawa University,Kakuma-machi, Kanazawa 920-1192, Japan * Corresponding author. Tel.: +81-76-234-4683; fax: +81-76-234-4683.E-mail address: yoneyama@t.kanazawa-u.ac.jp._
Abstract
For the application to the resection of brain tumor, force detecting micro gripper and force feedback system has been developed. Grasping force and pulling force at the gripper are transmitted to the master operating system where the surgeon feel the gripping force as force resistance and pulling force as friction on the finger surface.
The feeling at the master operator has been investigated through the gripping test on soft materials in various hardness applying force reflection bilateral control program. Topics: OS2: Medical devices and medical tools
© 2013 The Authors. Published by Elsevier B.V.
Selection and/or peer-review under responsibility of Professor Mamoru Mitsuishi and Professor Paulo Bartolo Keywords: Neurosurgery; manipulator; force feedback; master-slave; brain tumor
1. Introduction
Manipulator type robotic surgery has an advantage that few damages are given on the patient's body surface, and intelligent operation will be available beyond the manual handling devices [1,2]. In the resection of the brain tumor, application of robotic surgery is still difficult because the tumors are seated deep and surrounded by normal tissues and the route to the tumor is very narrow[3-8]. For the application of robotic manipulator to the resection of brain tumor, micro flexible manipulator with force feedback will be useful. Micro manipulator can approach to the tumor through narrow space. Force feedback will help the surgeon's operation by conducting the touch feeling on the tumor. On the base of these concepts, the authors have been developing a master-slave type micro manipulator with force feedback function[9-10]. In this paper, the development of micro gripper with force sensor, the design and fabrication of flexible manipulator, the
development of master manipulator and the basic result on the force feedback manipulating test will be shown.
2. Micro manipulator and operating system
2.1. Micro gripper with force sensor
There are three features in the developed manipulator. First is the small size in diameter. As a prototype of the micro manipulator for neurosurgery, the diameter of the closed gripper and the manipulator pipe are designed smaller than 3mm so that the manipulator can be inserted through the hole of the hard microscope tube in which the diameter of the hole is 3mm.
Second point is the flexibility of the manipulator. After passing through the hole, the top of the gripper should approach to the wide area under the vision of microscope by the flexion of the top of the manipulator. It is a hard task to compose flexible mechanism in the small manipulator.
Third feature is the force detecting performance of the gripper. For the resection at the deep area in the brain,
2212-8271 © 2013 The Authors. Published by Elsevier B.V.
Selection and/or peer-review under responsibility of Professor Mamoru Mitsuishi and Professor Paulo Bartolo doi: 10.1016/j.procir.2013.01.027
force detection and the force feedback will help the surgeon feel touching and hardness of the tissue surface and the resistance to remove the tumor besides the microscope vision.
Constructed micro gripper with force sensor is shown in Fig. 1. Strain gages are fit on the fixed clip in the gripper. The sensor can detect both vertical force and lateral force on the clip. Vertical force is accepted as gripping force and lateral force as pulling force. Cables from strain gages are wired through the inner tube in the manipulator.
Movable clip
Fig. 1 Force detecting micro gripper 2.2. Flexible manipulator
Flexible structure of the manipulator is shown in Fig.2. Outer tube can bend by pulling the wire inserted in the groove of the pipe. Inner tube can rotate in the outer tube to rotate the gripper at the top and is pulled to close the gripper.
Gum metal was used for both flexible parts in outer and inner tube. The flexion of the outer tube was analyzed by FEM Altair HyperWorks. Analyzed result on the outer tube is shown in Fig.3. By pulling the wire inserted through the holes in the rings of pipe, thin plate parts flex into the side direction. Pulling distance for the flexion of 30 degrees is about 1mm. Elastic limit of the
(c) Assembled flexible manipulator Fig.2 Flexible part of the manipulator tube
inclination angle of the outer tube was estimated larger than 30 degrees. Actual flexion of the fabricated outer tube is shown in Fig.4.
Fig.3 Analysis on the flexion of the outer tube
(a) Actual flexionby puffinglhewire
(b) Holes machined in the ring of tube
(e) Wire inserted through the hole
Fig.4 Actual flexion of the constructed outer tube
2.3. Master operating device
Master operating unit has been designed newly from the previous one to make compact and control all the slave motions in the right hand master motion. Designed operating unit is shown in Fig.5. The device has been designed so that the motion of the operating hand corresponds to the removing process of the tumor. If the surgeon pushes the pole forward, the slave manipulator translates forward. Rotation of the master pole corresponds to the flexion of the slave manipulator. Closing the lever on the master pole corresponds to the closing of the slave gripper. Touch sensors are installed on the surface of master pole to rotate the gripper at the top of the manipulator. Inclining the master pole to the
side direction corresponds to the entire rotation of the slave manipulator.
Force sensor is equipped on the finger holder to detect the force resistance on the finger as shown in Fig6.
Fig.5 Master operating device
Force sensor to detect the force resistance at the master finger
Fig.6 Force sensor to detect the force resistance
3. Control system
The developed controller is a bilateral controller constructed by a force reflecting servo controller for the master part and a virtual impedance model-based controller for the slave part. The force reflecting servo controller is used in order to feedback the forces exerted on the slave manipulator directly to the operator. Another merit of this construction is high operation performance at the master/operation device (e.g., if no force is exerted, the master part is power-assisted). The impedance controller is inserted in order to prevent operator forces/commands that are directly transmitted to the slave manipulator, and to reduce the effects of unexpected disturbances such as impacts and impulses. The details of the control law are as follows.
\Tm ~ Kf (fm sffs ) Cmxm f ~sffs~ Csspxs
where,
f = Cc (xm-spxs H Kc (xm~spxs )
c\ m p s ■>
Here, t,„, f„„fs, and/are the torque of the motor at the master, the master operation force, the slave contact force, and the driving force from virtual impedance model, respectively. The positions of the master and the slave manipulators are denoted as xm and xs, respectively. Cm and Cs, are the control gains. Cc, and Kc are the gains at the impedance model. sf and sp are scale factors. Kf is a force gain.
The control model and schema for the controller is shown in Fig. 7 and Fig.8, respectively.
(a) Control model at master part
Kc, Cc (b) Impedance model
Object
(c) Control model at slave part
Fig.7 Control model for the system
Fig.8 Force reflecting and impedance control schema
4. Basic force feedback test
A basic test of the gripping force feedback was implemented. Silicon rubber sheets of different hardness were prepared. One of the elastic modulus was 170kPa and other was 340kPa. The hardness of the brain tissue is estimated to be 170kPa but tumors may have various different hardness. The operator holds the operation pole and closes the finger to grip the rubber at the slave gripper under the vision of video scope as shown in Fig. 9. The purpose of this test is to examine how the gripping motion is transmitted to the slave gripper and how the gripping force reflects on the operator's finger.
A typical result is shown in Fig. 10. In case of soft rubber, increase of the gripping force with the angle is low and it is same in the master lever. In case of hard rubber, increase of the gripping force with the angle is rapid and it is same in the master lever. The operator feels the difference of the hardness from the gripping
(c) Gripper open (d) Gnpper close
Fig.9 Basic test on the force feedback on the finger
__ 0.8
£ 8 0.6
ForceS(hard) ForceS(soft)
0 20 40
Angle[deg]
(a) Force and angle at the gripper
Angle[deg]
(b) Force and angle at the master Fig. 10 Gripping force and force resistance at the master
difference of the hardness from the gripping angle and the force resistance.
5. Conclusions
Master-slave type micro manipulator system for neurosurgery is being developed. Using the force reflecting serve control, gripping force is transferred as the force resistance at the master finger. The surgeon will feel different hardness when gripping tumor or other tissues. We would like to study further to confirm that the feeling at the master finger supports to distinguish the brain tumor in the resection of brain tumor.
Acknowledgements
The authors wish to express appreciation to Prof. Junichiro Hamada, Yutaka Hayashi and Mitsutoshi Nakada who support the design of the system and evaluate the operability of the handling system.
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