Page 402 - Flexible Robotics in Medicine

Single-port multichannel multi-degree-of-freedom robot 395

to module 5. When the rods are pushed related to the flexible tubes, the arm can be driven
to move forward. Conversely, when the rods are pulled related to the flexible tubes, the arm
can move backward.

There are two main features for the arm, including the compliance and the variable
stiffness. The compliance is achieved by the modular continuum design and the driven
mode. Module 1 to module 3 is underactuated with two rotation joints. Wire 1 and wire 3
are coupled, so are wire 2 and wire 4. The variable stiffness is achieved by wire 1 and wire 3.
The stiffness of the arm is increasing with the tension of these wires, which can be controlled
by the driver in real-time. If we want to perform accuracy operation, the tension of wire 1
and wire 3 should be large enough, or else the tension can be smaller for safety
considerations.

17.2.4 The flexible wrist joint

The flexible wrist joint is shown in Fig. 17.3C. The flexible wrist joint related to the arm
allows the manipulator to be bent along the transversal direction. Two flexible hinges with
the materials of Ni-Ti alloy that has the excellent performance of superelasticity are used to
achieve the connection and flexibility. Two wires with flexible tubes attached to the module 1
are used to drive the motion of the wrist joint.

The primary purpose of designing a flexible joint is for safety consideration. When
manipulating the tissue of the human body during the NOTES operation, the flexible joint
can reduce the resulting forces in the robot structure and the drive-chain by storing short-
term energy [17].

17.2.5 The forceps

The forceps in Fig. 17.3D are used for the basic grasping in operation. It can be replaced
by other surgical tools such as the electrotome and the electric coagulation forceps,
according to the requirements of the surgery. Each forceps is driven by two wires with
flexible tubes and can be bent along the transversal direction. The grasping function is
achieved by the open-close motion of the forceps. Besides, the forceps can rotate in a broad
range.

17.2.6 The actuator

The transmission of wires with flexible tubes allows the actuator to be placed far away for
the terminal of the robot, which reduces its volume and weight. As shown in Fig. 17.3E, the
flexible tubes are attached to the support of the actuator, and the wires are attached to the
sliding blocks, which are driven by the motors via screws. The screws transfer the rotation