Page 30 - Flexible Robotics in Medicine

12 Chapter 1

1.4.3.2 Controllers and their evolution
Prevailing controllers are implemented by proportional-integral-derivative (PID),
proportional-integral (PI), or Jacobian of the system with feedforward structure, for
example, Conrad et al. [26] proposed a control framework for an interleaved continuum
rigid manipulator with two separate controllers, while the flexible segment controller has
a feedforward inverse kinematic conversion. Haraguchi et al. [31] realized position
control of a pneumatically driven snake surgical robot based on a PID cascade controller
with dynamic compensating as feedforward.
Recently novel controllers emerged, among which modeless (or data-driven) control
occupies a prominent position. Visual servo is the most representative one of modeless (or
data-driven) control, in which inverse kinematics is obtained from external variables such
as position obtained by cameras, depending less on the input parameters of robots, for
example, Wu et al. [73] proposed a hybrid control for the teleoperation of a snake robot
based on visual servo; Ouyang et al. [18] realized the visual servo control of the motion on
their newly designed snake-like manipulator; Yip and Camarillo [74] proposed a modeless
control featured by Jacobian estimation during the robot motion, and the control strategy
was realized by optimization of tensions and changes of the Jacobian.

As an evolution, a learning method has been used in modeless (or data-driven) control.
Xu et al. [75] applied regression methods on learning the nonlinear inverse kinematic model
of snake-like surgical robots; Lee et al. [76] proposed a generic control framework, which
learns the inverse model through online training without structural parameters; Mahler et al.
[77] used Gaussian process regression to learn a nonlinear kinematics with velocity as a
feature in the correction.
Besides, advanced control theories have been migrated on the motion control of snake-like
surgical robots, for example, Qi et al. [47] proposed a fuzzy controller for trajectory
tracking of snake robot’s end-effector based on a fuzzy polynomial model considering HN
performance and stability.

1.5 Conclusion

This survey summarized the state-of-the-art techniques on the recently developed snake-like
robots during the past 5 years that catered to surgical applications. Commercial products
and typical platforms were listed and compared from the aspects of actuation and the
intended surgical procedures. Mechanism designs of snake surgical robots were summarized
from the aspects of wire-driven, jointly connected, motor-driven, and novel designs.
Kinematic modeling, statics, and compensation for the uncertainties of modeling were
presented as prerequisites for motion planning and control. For the issues regarding the safe