# Review of Advanced Medical Telerobots
## 2 Medical Telerobotic Topologies
### Single-Leader Single-Follower Topology (SL/SF)
#### 2.1.2 Motor Augmentation through SL/SF Telebotic Surgery
This will significantly increase the accuracy of the operation since it significantly reduces the mental, cognitive, and physical load on the surgeons during operation [10; 11; 200; 209; 201; 202; 203; 204; 205; 206; 207; 208; 209; 210; 211; 200; 212]. Regarding the virtual fixture concept, it can be mentioned that leader-follower robotic systems can provide kinesthetic corrections, guidance, and avoidance for the surgeons based on the fusion of preoperative and intraoperative information [1; 67; 68; 111; 112]. Virtual fixtures (also known as \"active constraints\") are high-level algorithms that generate a kinesthetic no-fly-zone for telerobotic systems. For this, the algorithm would generate a virtual spatial manifold (the topology of which depends on the task) with specific stiffness (usually high stiffness). As a result, when the user hits the manifold in the space he/she would feel a resistive/repulsive force avoiding penetration to the virtual \"wall\". Although typically virtual fixtures do not suffer from communication delays, they still are virtually rendered, thus the stability of interaction would be challenged by the digitization (the sampling period). This challenge is pronounced since usually virtual fixtures have very high stiffness which would significantly reduce the margin of stability making the system susceptible to even the smallest delay caused by digitization. This concept has been discussed in the literature under the topic of \(Z\)-width which shows that each haptic system can safely display a limited range of impedances (this range is called \(Z\)-width). In 2014, [PERSON] et al., reviewed the existing algorithms found in the literature and detailed the various strategies to overcome this issue [67]. As mentioned, one main issue is reproducing a haptic interaction with highly rigid virtual walls. As mentioned, it has been shown that the sampled nature of the control loop can virtually generate non-passive energy and destabilize the whole control loop [84]. Recent works on this issue propose using the H\(\infty\) approach to design controllers capable of rendering stiff walls (\(<\)5000 N/m, much higher than with other control approaches) in an oscillation free manner and with actuator force limitation to avoid their saturation. For more viscous interactions such as the ones encountered in neurology, recent works are brought by [PERSON] et al., in [213]. The forbidden region virtual fixtures are to restrict surgeons' operation on sensitive tissues (such as ma jor arteries or delicate organs) through the generation of repulsive force field provided kinesthetically for the surgeon and through stopping the follower robot from hitting those no-fly zones [67; 111; 112]. This feature directly enhances the performance, accuracy, and safety of the operation by correcting the dangerous maneuvers by surgeons, (in particular, novice surgeons) and preventing damages [68; 111]. Using repulsive virtual fixtures, the telerobotic system can continuously monitor the motion of the surgeon for some forbidden regions [69; 214]. This technology has been very successful for operations on rigid tissues (such as bones) or structured organs such as retinas [68; 186; 187; 188; 215], but it faces significant technical difficulties for soft, highly dynamic, and unstructured soft tissues due to technical difficulties in registering preoperative and intraoperative information sources. There is active research on this topic under the umbrella of Dynamic Active Constraints (DACs) [123; 151] for realization on soft tissues. In an opposite scenario, using guiding virtual fixture telerobotic systems can assign novice surgeons to converge to a desirable trajectory or path (which can be annotated preoperatively by expert surgeons) [68; 69; 70; 71; 118; 216; 217].