Surgical Robots

One of the most challenging operations in clinical practice is intraocular eye surgery. Human eyes are delicate and highly complex organs, and the accuracy required for most intraocular surgeries ranges from 50−100 µm. Typically, intraocular surgeries are considered as a micro-surgical procedure, and during surgery, surgeons must carefully control the position and force of a small surgical instrument in an area of limited workspace with a delicate positioning accuracy. In order to address these challenges, robotic technology may come to the rescue. By using robot–assisted surgery, surgeons can perform microsurgeries with high levels of accuracy and dexterity, in a comfortable and ergonomic environment.

With the increasing development of microsurgical robots for vitreoretinal eye surgeries, the training process for novice surgeons can also be evaluated. The robotic surgical training systems may be used to provide the required accuracy and feedback to the novice surgeons with trainer direct involvement.

ARASH:ASiST stands for "ARAS haptic system for eye surgery training", which is an eye surgery training system developed to train novice surgeons in vitrectomy surgeries. This device has 3-DOF haptic interface, developed for use in a dual haptic eye surgery training system. Considering its mechanical features, this device provides the main required minimally invasive vitrectomy surgery properties, such as the remote center of motion and favorable kinematic workspace. ARASH:ASiST provides more than 90◦ in both rotational motions, 43.6mm in the insertion direction of the surgical instrument. Furthermore, it is equipped with two symmetrical weight counterbalances for weight compensation of the mechanism.

ARAS-Diamond is a spherical parallel manipulator. This robot is designed to perform as the slave robot in a robotic-assisted eye telesurgery system in which the surgeon operates on a master haptic console to send desired commands to this slave robot. This parallel robot provides two degrees of rotational motion and one degree of transmission motion, which is totally qualified for eye surgery. Owing to the parallel structure of the robot, higher structural stiffness, and improved position accuracy were obtained compared to that of other existing mechanisms, which makes it more appropriate for precise motions such as in eye surgeries. To provide a backdrivable transmission mechanism with high accuracy and zero backlashes, the manipulator utilizes two capstan drives for both actuators that provide rotational motions. 

This robot has an RCM (remote center of motion) point, which is a significant property needed for the implementation of minimally invasive surgeries. According to the spherical structure of the robot, all the links just have a pure rotational motion around the RCM point. The vitrector is mounted on the fourth link and has translational motion along the radial direction to the RCM point.

For the kinematic analysis of ARAS-Diamond, the position of the end-effector in the spherical coordinate system is considered as the generalized coordinate. By presenting a formulation based on the principle of virtual work, a linear form of robot dynamics is derived, and the obtained results are validated in MSC ADAMS. Furthermore, other terms affecting the robot dynamics are modeled, and by using the linear regression form of the robot dynamics with the required physical bounds on the parameters, the identification process is accomplished adopting the least-squares method with appropriate physical consistency. Finally, by using the criteria of the normalized root mean squared error (NRMSE) and using different trajectories, the accuracy of the identified dynamic parameters is evaluated.