# Review of Advanced Medical Telerobots
## 2 Medical Telerobotic Topologies
### Single-Leader Single-Follower Topology (SL/SF)
#### 2.1.1 Sensory Augmentation through SL/SF Telerobotic Surgery
The above-mentioned topic has been studied in the literature under the umbrella of haptics enabled telerobotic surgery, and [PERSON] et al. recently listed direct and indirect force-sensing solutions in [52]. The benefit of adding direct or indirect haptic feedback to robotic surgical systems has been studied extensively in the corresponding literature, some of which were conducted on the da Vinci surgical robotic system [100; 122; 123]. Clinical benefits have been reported such as (a) reduced average and peak forces on the tissue, and tissue damage [122; 126; 127]; (b) enhanced quality of knot tying, reduced frequency of suture breakage during surgery, enhanced force consistency [40; 99; 148], (c) realization of haptics-enabled tumor localization [125], and improved safety (for the patient) and lowered fatigue (for the surgeon) [148]. However, haptic feedback has not been achieved yet in commercialized examples [55; 101], and this is known to be one of the most significant limitations of existing telerobotic surgical technologies motivating researchers and industries to locate the challenges and invest in mitigation strategies [108; 109]. Still in 2017, there was no consensus about the best way to provide haptic feedback to the user, and also, no human factors and ergonomic (HFE) was available to prove the interest of each in practice [149]. There are two major challenges in this regard, namely: (a) instrumentation [136], (b) stability [7; 82; 85; 150]. Regarding instrumentation, it should be noted that sensors to be used on robotic surgical systems should be miniaturized, sterilizable, biocompatible, durable (to pass sterilization process), disposable, and cost-effective (since they need to be disposed of after a few uses to avoid infection transfer between patients and warranting safety) [136; 151; 135; 136]. The amplitude of the force signal is relatively high for laparoscopic surgeries and is very low for microsurgeries. Implementing a sensor that can measure multidimensional forces while providing a high signal to noise ratio and meeting all the above-mentioned requirements is a technically challenging task. There has been significant research on this topic, and as one solution (for some applications), optical force sensing, in particular fiber Bragg grating (FBG) sensor, is introduced as the technical solutions for this challenge [152; 153; 154; 155]. FBG sensors allow keeping expensive, unsterilizable, and technologically-challenging components outside of the patient's body while only some thin fiber-optics are connected to the tool, occupying a very small volume in space and measuring forces with high accuracy. FBG sensors are flexible and can be mounted on the body of the surgical tools, or inside the tools, or at the tip of the tool to measure different force features. Besides, the optical fibers are inexpensive, disposable, and biocompatible [153; 154; 155]. As a result, optical force sensing is known to be a future direction for enabling the next generation of telerobotic surgical systems in reflecting force sensation [156; 157; 158; 159; 160; 161; 162]. However, even if the forces are measured accurately, it is not trivial to reflect the force for the surgeon while guaranteeing stability [163; 164; 165; 166; 167]. It has been shown in the literature that high transparency of force reflection by leader robots and stability of telerobots are two opposing criteria [166; 167; 168; 169; 64; 3; 64; 85]. Thus, a haptics-enabled telerobotic surgical system that has near-to-ideal transparency in force reflection may suffer from poor stability and vice versa. The poor stability would sacrifice the safety of physical interaction between the patient and the robot, which is absolutely not acceptable in particular when robots interact with humans [1]. There are conventional stabilizers, such as wave variables, or time-domain passivity approaches, which degrade the transparency to guarantee the stability of the system.