# Cable-Driven Mechanism Models for Sensitive and Actuated Minimally Invasive Robotic Instruments
## 1 Introduction  
Classical surgery is performed by the surgeon's team, opening the body of the patient, in order to enter in the human body and to remove cancers or to perform other operations [1, 2]. Classical surgery includes many limits for the health of patients, during and after surgery [2]. Hemorrhages and bleeding occur more often in classical surgery than in robotic surgery. One reason for this is because the patient's body is opened. On the contrary, in robot-assisted surgery, only a few small incisions on the patient's body are performed to insert the tools in the body. This approach of robotic surgery is called minimally invasive robotic surgery [3, 4, 5]. An additional advantage of robot-assisted surgery is to reduce hand tremor, which can be transferred from the surgeon's hands to the patient's body in classical surgery. Robotic surgery is carried out using two robotic structures that ensure the physical separation of patients and surgeons (see Figure 1): a local (near the surgeon) and a remote station (near the patient) [4]. The remote part consists of robotic arms with minimally invasive robotic tools (or instruments) (MIRIs) (see Figure 2), controlled in teleoperation by the local part. The MIRIs (in the remote part), enter into the patient's body, and the surgeon (in the local part) controls their motions with her/his hands. Normally, the local station is equipped only with visual feedback for the surgeon. The tip of the MIRI can be constituted by forceps used for cutting, or tools for suturing or grasping, actuated by cable-driven systems [3, 4]. Figure 2 shows the da Vinci Research Kit (dVRK), available at the University of Verona (Italy). In the local station, the surgeon can interact using feet and hands with the console of the surgical robot. The surgeon has a view of the internal body of the patient because the endoscope (in the remote robot) is inside the patient's body, and it consists of a stereo camera. The remote instruments normally include two MIRIs. In dVRK, the cables of the MIRIs are connected to forceps on the tip and to four pulleys on the base,as shown in Figure 2. The four pulleys of MIRIs are connected to four motors on the remote robotic arm. The da Vinci robotic arm is an example of a cable-driven actuated system. This type of solution is useful when the robot end-effector must be very light. Motors are positioned away from the instruments, and the cables produce the end-effectors' motions. Many cable-driven actuated solutions are available in the literature for bio-robotic arms [6], robotic rehabilitation [7], building constructions [8], and many other applications [9; 10; 11]. Recently, a new cable-driven sensitive approach has been conceived, in which tension on cables are used to measure forces on the mobile part connected to the fixed part by using cables. Our past works, ref. [5] and ref. [12], focused on this new research direction [13; 14; 15; 16; 17; 18; 19]. Some recent work measures the tension on cables, in which the fixed part has bigger dimensions than the mobile part [15; 19]. Considering an application to MIRIs, our solution has a different approach: the fixed part has a smaller diameter with respect to the diameter of the MIRI and to the mobile part. In this paper, a comparison between our proposed solutions with different macroscopic and miniaturized scales is presented. One important problem in robotic surgery architectures is that tactile feedback is very difficult to implement on MIRIs. In order to increase surgeons' capabilities to carry out surgical operations, tactile information must be transferred to surgeons' hands [3; 4; 5].