Page 77 - Mechatronics for Safety Security and Dependability in a New Era

Ch13-I044963.fm Page 60 Tuesday, August 1, 2006 12:49 PM
Ch13-I044963.fm
60 60 Page 60 Tuesday, August 1,2006 12:49 PM

Figure 5: separation for sterilization; (left) forceps manipulator, (right) bending forceps

inserting distance of 300[mm] was realized using the 150[mm]-long linear stage. Rotational motion of the forceps
around the shaft was realized by transmitting the rotation of the motor with gear. The size of RCM part was
3 3
W250*H110*D60[mm ], and forceps driving unit was W140*H410*D70[mm ]. The whole weight was 4.5[kg].

Robotized forceps with a two-DOFbendingjoint anda grasper

We adopted minimal six DOFs to follow the motion of surgical procedure by surgeon. Robotized forceps had two
DOFs for bending motion and one DOF for the grasping motion of the jaw (Figure 4), resulting seven DOFs by
integrating four-DOF forceps manipulator. Bending and grasping motions were actuated with a tendon mecha-
nism, which had advantages in its mechanical simplicity and compactness and wide working range. Contrary,
elongation of the wire might lead to the decrease of tension and the poor controllability. Tension control mecha-
nism should be implemented to maintain the tension, however, it will cause the increase of size and complexity.
We used plastic wire made of polyarylate with low elastic property (approximately 0.8%)(Gravity Jigging, Fujino
line Corp., Japan). Each bending motion was independent from each other mechanically, and the path length of
the wire was constant despite of the bending angle of the other joint (Nishizawa K., et al. (2004)). We manufac-
tured various kinds of instruments; needle holder, grasper, and soft tissue grasper (Figure 4). Bending forceps con-
sisted of "forceps part" and "motor driving unit". The forceps was 10[mm] in diameter, 460[mm] in length. The
motor driving unit was 55[mm] in diameter and 160[mm] in length. The whole weight was 0.7[kg].

Separation mechanism for clinical appUcation

All surgical tools used in the operating room must be sterilized by steam (120[deg C], 2[atm]). Here, electric mo-
tors and circuit boxes could not be sterilized because they did not have water- and heat-resistant property. Thus,
we adopted "three parts method"(Hefti J.L., et al. (1998)); forceps manipulator and bending forceps were sepa-
rated into modules; autoclave-compatible part and non-sterilized part. Non-sterilized part was wrapped with sur-
gical drapes (sterilized clothes) except mechanical interface. At the mechanical interface, a sterilized intermediate
block is attached. Hereby, non-sterilized parts are not exposed, and sterilized module is attached to the intermedi-
ate block. With this method, sterilized module can be connected to non-sterilized part via intermediate block
without contamination. Forceps manipulator was separated into the RCM motion module (non-sterilization) and
forceps-driving module (sterilization compatible). They were connected using intermediate block. In the case of
bending forceps, it could be separated into forceps module (autoclave compatible) and motor driving unit
(non-sterilization) (Figure 5).

EXEPERIMENTAL RESULTS

Forceps manipulator