# Review of Advanced Medical Telerobots
## 2 Medical Telerobotic Topologies
### Multilateral Teleoperation
#### 2.3.4 Trilateral Teleoperation  
Trilateral teleoperation is a specific case of multilateral systems in which the system has three terminals between which the motion and force profiles get exchanged (see Figure 6). Due to the particular use of this architecture, here, we have separately discussed trilateral teleoperation. This architecture has been used in three different configurations, as explained below. Human-Machine Shared Control (HMSC)  
This configuration consists of one operator/leader robot, one autonomous agent (please see Section 3 for more details), and one follower robot [206, 251, 299, 250, 290, 291, 292, 293, 294, 295, 296, 297, 298, 299, 300]. The configuration has also been seen as a variation of SL/SF architecture, which is augmented with artificial intelligence. In this setting, the operator's actions and the task are monitored by the autonomous agent, which refines the leader's command that is to be given to the follower robot [206, 216, 299]. Among the scenarios that this configuration has been suggested for, are surgical training and supervised autonomous surgery. For motor training, the trainee (at the leader side) shares the control of the teleoperated task with the autonomous agent. Haptics cues generated by the autonomous agent can be provided to guide gently or to impose a trajectory strictly to be followed [206, 216, 299]. For surgical  
Figure 5: Multilateral topologies used in telerobotics, \(n\) is the number of network ports/terminals. (**a**) Single leader–multi follower (**b**) multi leader–multi follower (Images ©2020 Intuitive Surgical, Inc.). autonomy, the autonomous agent is in charge of monitoring and conducting certain aspects of a task in collaboration by (and under the supervision of) the surgeon, to help reduce the difficulty of repetitive tasks for a surgeon [251,304] (Please see Section 3). In non-medical scenarios, HMSC systems have been used in telemanipulation, maintenance, and repair procedures for space applications (such as space robots) to take advantage of the intelligence of an operator for decision making and teleoperation, as well as autonomous control of the agent in the loop [300, 301, 302, 303]. This configuration refers to structures that have two leader stations for the cooperation of two operators on one follower console. This collaboration helps improve the task execution in comparison with the same task done individually [273]. The concept of haptic-enabled negotiation between two operators can be made feasible using this  
more affected and less affected sides under the supervision of the therapist and is classified under a mirror rehabilitation framework, which is a well-known technique for promoting cross-cortex activity of the brain [247, 253, 254]. In the context of surgical training, DUST topology has been used for EIL haptics-enabled training scheme. For this, the expert and the novice surgeons control the two leader robots while the follower robot is to conduct tasks on a physical phantom of the surgical site designed for training. Using this architecture while the expert surgeon is conducting the task, using a rigid virtual fixture implemented at the novice's side, the novice would learn how to manipulate and control. Besides, when the novice surgeon is performing the task, the expert surgeon can provide corrections and cues since there is a haptics coupling between the two leader robots. In addition, when the two surgeons conduct the task, the system can adaptively tune the authority level and the stiffness of the virtual fixture. In this way, if the novice surgeon is generating high-quality motions (which can be quantified through comparison with the expert surgeon's motion on the fly and during the operation, and based on measures such as trajectory differences, smoothness, etc. ), the system can allow for higher authority and lower stiffness of the dynamic virtual fixture. Examples of such designs can be found in the literature [258, 260, 261, 262, 263, 264, 265, 266, 4].