Page 27 - Flexible Robotics in Medicine

Slender snake-like endoscopic robots in surgery 9

1.3.3 Hysteresis and compensation

Brought by the tendon-driven mechanism, the friction force between the backbones and robot
body introduces asymmetric hysteresis displayed as backlash. Moreover, the elongation of the
actuation backbone is introduced by friction force and actuation force [33]. The backlash and
elongation of actuation wires are the main factors that influence the accurate modeling and
control of a snake-like surgical robot. Camarillo et al. [53], Kesner and Howe [54],and Gaoet al.
[55] recorded the hysteresis of the manipulator tip trajectory in the simulation and experiments.
For solving the problem of hysteresis, Kato et al. [41] built an extended forward kinematic
mapping method to improve the prediction of the posture with hysteresis included. Another way
of the solution is to compensate for the backlash. Kesner and Howe [54] built a model to predict
the width of the backlash zone and proposed the compensation method based on the offset values
of the backlash zone. For the backlash compensation, Xu and Simaan [3] implemented a
simplified redundancy resolution to update the instantaneous kinematics of the robot by adding a
modifier to the actuation parameter; Simaan et al. [40] proposed an actuation compensation for
both of the joint space and configuration space, with the compensation parameter obtained by
linear recursive estimation. For the compensation of elongation, Bajo et al. [12] proposed the
actuation compensation based on the elastic parameter of the backbones and energy information
of the robot. Lau et al. [33] built an elongation model of an SMA-actuated cable-driven robot and
handled the elongation and backlash by modifying trajectories in one model.

1.4 Human machine interaction

Aiming at MIS or NOTES, surgical robots have to go deep into the human body. For surgeons,
access to and manipulation of the target area is through the transmission of the mechanisms, and
the operation vision is enabled by endoscopic camera or imaging through radioactive methods.
Surgeons make the operation plan and manipulate the robots according to the feedback
information collected by the robot system or external imaging systems during surgery. Therefore
the commands and feedback interchange between surgeons and robots are essential to ensure a
successful surgery, which highlights the role of human machine interaction in surgical robotic
research and developments. For snake-like surgical robots, the human machine interaction
becomes even more challenging because hyperredundant body shape brings difficulty in locating,
configuration derivation, and motion planning. Moreover, most of the snake robots adopt the
wire-driven mechanical design, which complicates the modeling and control.

1.4.1 Shape/force sensing

Tracking the position of the end-effector and configuration of the robot is the premise of safe
access to human anatomy. However, the narrow access path into the target area cannot afford
enough space for active measurement. It only allows passive measurement, such as