Patent Publication Number: US-2022226061-A1

Title: Robotic microsurgical assembly

Description:
This application is a Continuation of U.S. patent application Ser. No. 16/605,121 filed 14 Oct. 2019, which is a National Stage Application of PCT/162018/052591, filed 13 Apr. 2018, which claims the benefit of Serial No. 102017000041991, filed 14 Apr. 2017 in Italy, and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above-disclosed applications. 
    
    
     FIELD OF THE INVENTION 
     It is an object of the present invention a robotic surgical assembly. 
     In particular, the present invention relates to a robotic microsurgical assembly. 
     The present invention relates to a robotic microsurgical assembly of the type comprising a master tool manipulator and a surgical instrument. 
     The present invention also relates to a slave assembly as well as to a surgical instrument. 
     BACKGROUND 
     Robotic assemblies for surgery or microsurgery comprising multi-joint robotic arms terminating with surgical instruments are known in the field. For instance, document U.S. pat. No. 7,155,316 discloses a robotic assembly for performing brain microsurgery under MRI (Magnetic Resonance Imaging) guidance comprising an MRI-based image acquisition system and two multi-joint arms, each with three rotary joints with vertical axes to avoid direct gravity loads (as shown for instance in  FIG. 7  of said document U.S. Pat. No. 7,155,316), each connected to its respective end-effector endowed with an internal degree of freedom of motion for gripping. 
     It is also notable that the execution of the principal surgical primitives, such as tissue tensioning and anastomotic suturing, requires the ability to orient the surgical instrument tip in a large spatial cone of directions and to rotate the instrument around its longitudinal axis (roll), for example to guide the needle through the tissue with the tip of the needle holder instrument, in a similar manner as the human hand is jointed at the wrist and the elbow. 
     In order to simplify the miniaturization of a surgical instrument, the document WO-2010-009221 indicates the advantageous opportunity of reducing the number of actuation tendon terminations, associated to three degrees of freedom, from six to four, exploiting for actuation the torque that cables terminated on the yaw link apply on the pitch link (see  FIG. 4 -A of cited document) and requires to such purpose to pull and release selectively such cables, thanks to a kinematic mechanism comprising a number of gears. Moreover, the driving system described requires that each end of an actuation tendon is attached to a winch, that selectively winds the tendon inducing the pull. The presence of mechanical aspects such as said winch and said teeth, which are notoriously subject to lost motion, creates a difficult to drive a miniature articulation, because lost motion in the drive system is translated into an angular play at the joint, that increase as the articulating device gets smaller. Said driving system is also unsuited to keep a low preload on the actuation cables to further limit friction and wear. 
     Moreover, the solutions described for tendon termination comprise tortuous paths meant to trap the tendon in some sections. Such solutions require the use of cables that are sufficiently resistant to survive such trapping, such as steel cables or cables with larger diameter than otherwise required. 
     The proximal tension in a proximal portion of a tendon, such as a proximal portion extending proximally than an intermediate portion of the same tendon contacting a structural member or link, and the tension in the intermediate portion of said tendon contacting said structural member, whenever the tendon is pulling, are related by the capstan equation. With the tendon pulling and is defined as positive, the tension in said tendon after crossing said structural member or link is reduced in consequence of the sliding friction between the tendon and the structural member surface by a factor exponentially related to the product of the sliding friction coefficient between the tendon material and the structural member material, and the winding angle between the tendon and the structural member. 
     The capstan equation holds true also in its differential form that can be integrated along the total winding angle. So it holds true also for arbitrary shapes of the winding surface by using for winding angle the total change in tendon direction as a result of the contact with the structural member. A significant additional sliding friction not accounted for by the capstan equation is present in any sharp point contact between tendon and structural member, which should be thus avoided to minimize friction. 
     A number of wrist designs avoid altogether sliding friction on the tendons by making use of idle pulleys to route the tendon around the links, such as in WO-2014-151952 and U.S. Pat. No. 6,676,684. Their miniaturization is limited by the minimum feasible diameter of said idler pulleys. 
     Specifically, U.S. Pat. No. 6,676,684 shows actuation cables for actuating the links that wrap around an idle pulley (ref. 68) rotatably connected to said link. Therefore, the actuation cables avoid to slide onto the surfaces of the respective pulley, and rather the pulley rolls and the respective actuation cable is locally stationary with respect to the pulley surface. Moreover, the distal link comprises a rounded termination surface (ref. 58.6) around which the actuation cable is wound and firmly secured, in order to move the distal link. 
     U.S. Pat. No. 6,840,938 shows a three link wrist assembly and a yaw cable terminated on the third link that is routed with idle pulleys rotatably connected to the first link and second link and avoids slide onto the surfaces of the respective pulley, and rather the pulley rolls and the respective actuation cable is locally stationary with respect to the pulley surface. In other words, the yaw cable avoids contacting the first link and the second link on any sliding contact surfaces. 
     Other similar examples are shown in document US-2002-120252, wherein the actuation cable is fixed and wound around a pulley rotatably connected to a respective link to transmit motion to the link, and wherein termination of actuation cable is firmly secured to the link to be moved requiring the cable termination being stationary in respect to the link. 
     A number of wrist designs, in the effort to miniaturize the wrist subassembly, have the tendons contacting the structural bodies of the intermediate links and sliding on them to move the more distal links, such as described for example in US-2015-0127045, WO-03-001986, WO-2010-009221, US-2017-0020615 ( FIG. 5B ) and US-2016-0051274. 
     In all such cases, the designer is making sure he/she is limiting the sliding friction to a minimum possible by minimizing the tendon winding or wrap angle over the structural bodies of the links. Specifically in all such designs the tendons are routed along longitudinal holes or channels that pass through the structural body of the link. As a result, in the above design, when the wrist in its straight configuration, the tendons have practically zero winding angle on the structural bodies of the intermediate links, while when the wrist is bent at close to 90 degrees, the total winding angle of the tendons attached to the most distal link is close to 90 degrees. 
     The unavoidable requirements to fabricate holes or guiding channels in the structural body of the link and to feed in said holes or guiding channels said tendons represent a severe limitation to the miniaturization of such designs. It should be noted the essential role of such holes in constraining the tendon to stay close to the wrist subassembly. In fact, as the wrist subassembly takes its different configuration the tendon is constrained by different sides of the holes&#39; surface which necessarily have to surround it completely. In other words, in all mentioned documents, the routing of tendons through holes is an essential feature of the design. 
     A number of wrist designs, such as described in US-2003-0135204, avoid the use of both idle pulleys and the use of holes or guiding channels in the structural body of the intermediate link. Said design employs cylindrical protrusions, on which the tendon slides, to guide the tendons to reach the most distal links. The winding angle of such tendons on the structural link one is still kept to a minimum, that can be estimated around 10 degrees from the drawings, when the wrist in in its straight configuration. In fact, such tendons are deflected by said cylindrical protrusions toward the center of the links. The design still make use of holes in the structural body of the base link to constrain the tendons to stay within the diameter of the link members when the distal links are bent (with a yaw movement). Fabrication of holes in the structural body of the base (first) link of the body remains a limiting factor for miniaturization. 
     Hence, there is a felt need to provide a tendon, or actuation cable, for a medical instrument with characteristics that render it suitable for extreme miniaturization without compromising its resistance or reliability in use. 
     Furthermore, there is a felt need to provide a tendon for a medical instrument that is suitable for gliding over at least one portion of said instrument with improved performance in terms of friction with respect to known solutions. 
     Furthermore, there is a felt need to provide a tendon for a slave surgical instrument exclusively meant to work under tensile load applied at its endpoints, without comprising solutions that might result in deflecting the path of the tendon, that would diminish its resistance. 
     It is felt the need to reduce the friction between a tendon and the surface on which said tendon slides and at the same time it is strongly felt the need to miniaturize surgical instruments for robotic surgery. 
     Solution 
     A scope of the invention described here is to overcome the limitations of known solutions as described above and to provide a solution to the needs mentioned with reference to the state of the art. 
    
    
     
       FIGURES 
       Further characteristics and advantages of the invention will appear from the description reported below of preferred embodiments, which are given as examples and are not meant to be limiting, which makes reference to the attached figures, in which: 
         FIG. 1  is a perspective view of a robotic surgical assembly, according to an embodiment, wherein sketches depict a patient a surgeon; 
         FIG. 2  is a perspective view of a robotic surgical assembly, according to an embodiment, wherein a sketch depicts a patient; 
         FIG. 3A  is a block diagram of a robotic surgical assembly, according to an embodiment; 
         FIG. 3B  is a block diagram of a robotic surgical assembly, according to an embodiment; 
         FIG. 3C  is a block diagram of a robotic surgical assembly, according to an embodiment; 
         FIG. 4  is a perspective view of a portion of a slave manipulator connected to a surgical instrument, according to an embodiment; 
         FIG. 5  is a plan view of a portion of a slave manipulator connected to a surgical instrument, according to an embodiment; 
         FIG. 6  is a perspective view of a portion of a slave manipulator disconnected from a surgical instrument, according to an embodiment; 
         FIG. 7  is a sketch depicting a cross-section of a portion of a slave manipulator and a surgical instrument, according to an embodiment; 
         FIG. 8  is a perspective view of a jointed subassembly, according to an embodiment, wherein some parts are sectioned for sought of clarity; 
         FIG. 9  is a perspective view of a jointed subassembly, according to an embodiment; 
         FIG. 10  is a perspective view of a jointed subassembly, according to an embodiment; 
         FIG. 11  is a perspective view of a portion of a jointed subassembly, according to an embodiment; 
         FIG. 12  is a perspective view of a link, according to an embodiment; 
         FIG. 13A  is a perspective view of a link, according to an embodiment; 
         FIG. 13B  is a perspective view of a link, according to an embodiment; 
         FIG. 14  is a perspective view of a link, according to an embodiment; 
         FIG. 15  is a perspective view of a link, according to an embodiment; 
         FIG. 16  is a perspective view of a jointed subassembly, according to an embodiment, wherein the tendons are not shown; 
         FIG. 17  is a sketch in plane view of a portion of a jointed subassembly, according to an embodiment, wherein tendons are shown; 
         FIG. 18  is a perspective view of a jointed subassembly, according to an embodiment; 
         FIG. 19  is a perspective view of a jointed subassembly, according to an embodiment, wherein a double-jointed joint is shown; 
         FIG. 20  is a perspective view of a jointed subassembly, according to an embodiment; 
         FIG. 21  is an exploded view of the jointed subassembly depicted in  FIG. 20 , wherein the tendons and the pins are not shown for sought of clarity; 
         FIG. 22  is a perspective view of a joint of the jointed subassembly, according to an embodiment; 
         FIG. 23  is a perspective view of a joint of the jointed subassembly, according to an embodiment; 
         FIG. 24  is a perspective view of a jointed subassembly, according to an embodiment; 
         FIG. 25  is a perspective view of a portion of the jointed subassembly shown in  FIG. 24 , wherein the tendons are not shown for sought of clarity; 
         FIG. 26  is a perspective view of a jointed subassembly, according to an embodiment; 
         FIG. 27  is a plane views of a jointed subassembly showing three configurations of the jointed subassembly, according to an embodiment; 
         FIG. 28  is a plane views of a jointed subassembly showing three configurations of the jointed subassembly, according to an embodiment; 
         FIG. 29  is a plane views of a jointed subassembly showing three configurations of the jointed subassembly, according to an embodiment; 
         FIGS. 30, 31 and 32  are perspective views of a jointed subassembly, according to some embodiments; 
         FIG. 33  is a perspective view of a link and a portion of a tendon, according to an embodiment; 
         FIG. 34  is a perspective view of the link and the tendon shown in  FIG. 33 , depicted from the point of view indicated by the arrow XXXIV of  FIG. 33 ; 
         FIG. 35  is a perspective view of a link, according to an embodiment; 
         FIGS. 36 and 37  are plane views showing a jointed subassembly having transparent parts for sought of clarity and at least one tendon, according to some embodiments; 
         FIGS. 38 and 39  are plane views showing a jointed subassembly having transparent parts for sought of clarity and a tendon, according to some embodiments; 
         FIGS. 40 and 41  are plane views showing a jointed subassembly having transparent parts for sought of clarity and at least one tendon, according to some embodiments; 
         FIG. 42  is a sketch in plane view showing a configuration of a jointed subassembly, according to an embodiment, wherein a tendon describes a total winding angle; 
         FIG. 43  is a sketch in plane view showing a configuration of a jointed subassembly, according to an embodiment, wherein a tendon describes a total winding angle; 
         FIG. 44  is a sketch in plane view showing a configuration of a jointed subassembly, according to an embodiment, wherein a tendon describes a total winding angle; 
         FIG. 45  is a sketch in plane view showing a configuration of a jointed subassembly, according to an embodiment, wherein a tendon describes a total winding angle; 
         FIG. 46  is a sketch showing a cross-section of a link, according to an embodiment, wherein a tendon describes a local winding angle; 
         FIG. 47  is a sketch showing a cross-section of a link, according to an embodiment, wherein a tendon describes a local winding angle. 
     
    
    
     DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS 
     According to a general embodiment, a robotic surgical assembly  1  comprises a slave manipulator  3 , a surgical instrument  70 , connectable to said slave manipulator  3 . 
     Said surgical instrument  70  comprises a jointed subassembly  5 . 
     Said jointed subassembly  5  comprises at least a first link  6 , a second link  7  and a third link  8 ; 
     According to an embodiment, a robotic microsurgery assembly  1  comprises at least one master tool  2 , suitable to detect a manual command, at least one slave manipulator  3  and at least a surgical instrument  70 , and at least one control unit  4  configured to receive at least a first command signal  59  comprising information about said manual command and to send a second command signal  60  to at least one actuator  25  in said slave manipulator  3  to control said surgical instrument  70 . 
     According to an embodiment, said surgical instrument  70  is a slave surgical instrument  70 . According to an embodiment, said surgical instrument  70  is a medical instrument  70 . 
     Said surgical instrument  70  comprises a jointed subassembly  5  comprising at least a first link  6 , a second link  7  and a third link  8 . 
     Said first link  6  and said second link  7  are associated in a first joint  14  providing a degree of freedom between said first link  6  and said second link  7 . 
     Said second link  7  and said third link  8  are associated in a second joint  17  providing a degree of freedom between said second link  7  and said third link  8 . 
     Said surgical instrument  70  comprises at least a tendon  19  for moving a degree of freedom. 
     Said at least one tendon  19  is suitable for moving said third link  8  in respect of at least said second link  7 . According to an embodiment, said surgical instrument  70  comprises at least a pair of tendons  19 ,  20  for moving a degree of freedom. According to an embodiment, said pair of tendons  19 ,  20  is suitable for moving said third link  8  in respect of at least said second link  7 . 
     According to a preferred embodiment, said tendon  19  comprises a tendon proximal portion  26 , suitable to be associated to at least an actuator  25 , said actuator being preferably not placed in said jointed subassembly  5 , a tendon distal portion  27 , secured to said third link  8 , and a tendon intermediate portion  28 , extending between said tendon proximal portion  26  and said tendon distal portion  27 . For example, said at least one actuator  25  is located in an actuator compartment  69  portion of said slave manipulator  3  placed upstream with respect of the jointed subassembly  5 . 
     At least one between said first link  6  and said second link  7  comprises at least one tendon contact surface  18  on which said tendon  19 , and preferably said tendon intermediate portion  28 , slides remaining in contact with said at least one tendon contact surface  18 , defining one or more sliding paths  65  on said at least one tendon contact surface  18 . In this way said at least one tendon contact surface  18  is a tendon sliding surface  66 . 
     According to a preferred embodiment, said at least one tendon sliding surface  66  of either said first link  6  and said second link  7  is a smooth surface having a surface profile without sharp edges. 
     According to a preferred embodiment, said at least one tendon contact surface  18  of either said first link  6  and said second link  7  is a smooth surface having a surface profile without sharp edges. 
     According to a preferred embodiment, said at least one tendon contact surface  18  of either said first link  6  and said second link  7  is a tendon sliding surface  66 , on which said tendon  19  slides having local relative motion with said at least one tendon sliding surface  66 , while remaining in contact with said at least one tendon contact surface  18 . In other words, according to an embodiment, said at least one tendon contact surface  18  on which said tendon intermediate portion slides, is a tendon sliding surface  66 . In other words, according to one embodiment, a local relative sliding motion takes place between said tendon and said at least one tendon contact surface  18  when the jointed device configuration changes from a first configuration to a second configuration. In other words, according to one embodiment, a local sliding friction force is generated between said tendon and said at least one tendon contact surface  18  during motion of the jointed device. 
     According to one embodiment, the term “slides” and the term “sliding” both refer to contact with local relative sliding motion. According to one embodiment, the term “slides” and the term “sliding” both refer to contact that generates local sliding friction force. According to one embodiment, the term “slides” and the term “sliding” both avoid referring to contact without local relative sliding motion, such as contacts between a tendon and an idle pulley and such as contact between a tendon and a surface on which said tendon is terminated and is winded. 
     According to a preferred embodiment, said at least one tendon contact surface  18  of either said first link  6  and said second link  7  is a tendon sliding surface  66 , on which said tendon  19  slides remaining in contact with said at least one tendon sliding surface  66 . In other words, according to an embodiment, said at least one tendon contact surface  18  on which said tendon intermediate portion slides, is a tendon sliding surface  66 . According to an embodiment, said third link  8  comprises at least one tendon contact surface  18  and said tendon touches said tendon contact surface  18  of said third link  8  avoiding to slide thereon. According to an embodiment, said tendon distal portion  27  is unsuitable for sliding on a tendon contact surface  18 . 
     According to an embodiment, said sliding path  65  has substantially a prevailing longitudinal extension. According to an embodiment, said sliding path  65  is the imprint that the tendon  19  defines on said tendon sliding surfaces  66 . According to a preferred embodiment, each of said one or more sliding paths  65  is a continuous path. According to an embodiment, said tendon  19  and said tendon sliding surface  66  exchange local frictional forces as a result of the local relative motion. According to an embodiment, said tendon slides on said at least one tendon contact surface  18  along, or parallel to, the direction of its longitudinal development T-T, or tendon longitudinal path T-T. According to an embodiment, said tendon avoid to slide on said at least one tendon contact surface  18  in a direction transversal to the tendon longitudinal path T-T. According to an embodiment, said tendon longitudinal path T-T is stationary over the time. According to an embodiment, said one or more sliding paths  65  are coincident or parallel to a portion of said tendon longitudinal path T-T. 
     According to an embodiment, said sliding path  65  comprises and proximal or initial sliding path end, characterized by an initial tendon path direction immediately before said initial sliding path end, and a distal or final sliding path end, characterized by a final tendon path direction immediately after said final sliding path end. According to an embodiment, said tendon intermediate portion  28  is deflected by said at least one of first link  6  and second link  7 . According to an embodiment, said tendon intermediate portion  28  is deflected by said at least one of first link  6  and second link  7  from an initial tendon path direction to final tendon path direction. According to an embodiment, said tendon intermediate portion is deflected by said at least one of first link  6  and second link  7  by a tendon deflection angle. According to an embodiment, said tendon deflection angle is measured as the angle between said initial tendon path direction and said final tendon path direction. According to an embodiment, said tendon intermediate portion is deflected by said at least one of first link  6  and second link  7  by one or more tendon deflection angles. According to an embodiment, a total deflection angle is the sum of all said tendon deflection angles. According to an embodiment, in at least one configuration of said jointed subassembly  5 , said total deflection angle α+ß is equal to or greater than 120 degrees. According to an embodiment, a straight configuration of said jointed subassembly has said link  2  and  3  at the center of their joint range of motion. According to an embodiment, in said straight configuration of said jointed subassembly  5 , said total deflection angle α+ß is equal to or greater than 90 degrees. 
     According to a preferred embodiment, said total tendon deflection angle α+ß is said total winding angle α+ß. 
     According to a preferred embodiment, said at least one tendon longitudinal path T-T is tangent to said at least one tendon sliding surface  66  of either said first link  6  and said second link  7  at said initial sliding path end. According to a preferred embodiment, said at least one tendon longitudinal path T-T is tangent to said at least one tendon sliding surface  66  of either said first link  6  and said second link  7  at said final sliding path end. According to a preferred embodiment, for every jointed assembly configuration, said at least one tendon longitudinal path T-T is a smooth continuous curve, without angles. 
     Advantageously, the sum of all the sliding paths  65  of all the tendon sliding surfaces  66  of said first link  6  and of said second link  7  defines a total winding angle α+ß. 
     According to a preferred embodiment, the sum of all the sliding paths  65  of all the tendon sliding surfaces  66  defines a total winding angle α+ 261  . 
     According to an embodiment, the sum of all the sliding paths  65  of all the tendon sliding surfaces  66  sweeps a total winding angle α+ 261 . According to an embodiment, the sum of all the sliding paths  65  of all the tendon sliding surfaces  66  is covered by a total winding angle α+ß. 
     According to an embodiment, a single sliding path of a tendon sliding surface  66  of one link between said first link  7  and said second link  8  defines a local winding angle α or ß. According to an embodiment, the sum of all said local winding angles defines said total winding angle α+ß. According to an embodiment, a single sliding path  65  of a tendon sliding surface  66  of one link between said first link  7  and said second link  8  defines a first local winding angle α. According to an embodiment, a single sliding path  65  of a tendon contact surface  18  of one link between said first link  7  and said second link  8  defines a second local winding angle ß. 
     According to an embodiment, said winding angle and said total winding angle refers to contact that generates local sliding friction force between said tendon and said at least one link between said first link  7  and said second link  8 . According to an embodiment, said winding angle and total winding angle refers to contact that generates local sliding friction force between said tendon and said at least one link between said first link  7  and said second link  8  that increases with said winding angle. 
     Advantageously, in at least one configuration of said jointed subassembly  5 , said total winding angle α+ß is equal to or greater than 120 degrees. 
     According to an embodiment, said total winding angle (α+ß) is equal to or greater than 90 degrees when said jointed subassembly  5  is in its straight configuration. 
     According to an embodiment, the term “configuration” indicates a spatial geometrical positioning of said jointed subassembly  5 . According to an embodiment, the term “configuration” indicates the relative spatial positioning and orientation of the links  6 ,  7 ,  8  forming said jointed subassembly  5 . According to an embodiment, the term “straight configuration” indicates that the kinematic chain formed by said jointed subassembly  5  is substantially unfolded and/or extended to its maximum elongation. 
     According to an embodiment, one between said first link  6  and said second link  7  comprises at least two tendon contact surfaces  18 , on which said tendon  19 , and preferably said tendon intermediate portion  28 , slides remaining in contact with both said at least two tendon sliding surface  66 , defining said one or more sliding paths  65  on said at least two tendon contact surfaces  18 . 
     According to an embodiment, said first link  7  comprises at least one tendon contact surfaces  18 , on which said tendon  19 , and preferably said tendon intermediate portion  28 , slides remaining in contact with said at least one tendon sliding surface  66 , defining said one or more sliding paths  65  on said at least one tendon sliding surface  66 , and said second link  8  comprises at least one further tendon contact surfaces  18 , on which said tendon  19 , and preferably said tendon intermediate portion  28 , slides remaining in contact with said at least one further tendon sliding surface  66 , defining said one or more sliding paths  65  on said at least one further tendon sliding surface  66 . 
     According to an embodiment, said jointed subassembly  5  comprises at least two tendon contact surfaces  18  being said tendon sliding surfaces  66 , on which said tendon  19 , and preferably said tendon intermediate portion  28 , slides remaining in contact with both said at least two tendon sliding surfaces  66 , defining said one or more sliding paths  65  on said at least two tendon sliding surfaces  66 . 
     According to an embodiment, said third link  8  comprises at least a tendon contact surface  18  which is unsuitable for said tendon  19 , and preferably for said tendon distal portion  27 , to slide thereon. 
     According to an embodiment, each of said local winding angles is defined as the angle subtended to said tendon sliding surface  66 . According to an embodiment, said total winding angle α+ß is defined as the sum of all said local winding angles. 
     According to an embodiment, each of said local winding angles is defined as the angle formed by the two orthogonal lines to said tendons directed along said tendon longitudinal path T-T and defined in portions of said tendons that delimits the contact path  65  on said tendon sliding surface  66 . 
     According to an embodiment, each of said local winding angles is defined as the angle formed by the two tendon longitudinal path T-T directions and defined in portions of said tendons that delimits the contact path  65  on said tendon sliding surface  66 . 
     According to an embodiment, said at least one tendon sliding surface  66  comprises a proximal contact surface border  67  and a distal contact surface border  68  which delimit said tendon contact surface  18  along said tendon longitudinal path T-T, wherein said proximal contact surface border  67  is located proximally in respect of said distal contact surface border  68 . According to an embodiment, each of said local winding angles is defined as the angle formed by the orthogonal lines to said tendon longitudinal path T-T evaluated immediately before said proximal contact surface border  67  and said tendon longitudinal path T-T evaluated immediately after said distal contact surface border  68 . 
     According to an embodiment, said at least one tendon contact surface  18  comprises a proximal contact surface border  67  and a distal contact surface border  68  which delimit said tendon sliding surface  66  along said tendon longitudinal path T-T, wherein said proximal contact surface border  67  is located proximally in respect of said distal contact surface border  68 . According to an embodiment, each of said local winding angles is defined as the angle formed by said tendon longitudinal path T-T direction evaluated immediately before said proximal contact surface border  67  and said tendon longitudinal path T-T direction evaluated immediately after said distal contact surface border  68 . 
     According to an embodiment, each local winding angle α or ß is defined on a surface on which said tendon slides while remaining in contact, even if said surface is discontinuous or has sharp points. 
     According to an embodiment, each local winding angle α or ß is measured with reference to the center of the osculator circle to a single tendon sliding surface  66 . 
     According to an embodiment, all contact points of a single tendon sliding surface  18  of a link embraces a portion of said link in such way to define a local winding angle α or ß. 
     According to an embodiment, said total winding angle α+ß is comprised between 60 degrees and 300 degrees. 
     According to an embodiment, said total winding angle α+ß is comprised between 90 degrees and 270 degrees. 
     According to an embodiment, each link  6 ,  7 ,  8  has a link encumber. According to an embodiment, said at least one tendon contact surface  18  delimits at least partially said link encumber of a link. 
     According to an embodiment, said tendon contact surface  18  is cylindrical. According to an embodiment, said tendon sliding surface  66  is a portion of a cylindrical surface. 
     According to a preferred embodiment, said tendon is made of polymeric material. 
     According to an embodiment, said tendon is made of a material chosen in the group consisting of polyethylene, ultra-high molecular weight polyethylene or UHMWPE, Kevlar®, Vectran®, Zylon®, polybenzobisoxazole, carbon fibers and combinations thereof. 
     According to a preferred embodiment, said tendon intermediate portion  28  is made of polymeric material. In this way, it is possible to provide said tendon intermediate portion  28  with less friction, less wear over the life time, thus less upkeep, and it is possible to realize said tendon intermediate portion  28  having inferior diameter in respect of tendons in other materials. 
     According to an embodiment, said tendon intermediate portion  28  is made of a material chosen in the group consisting of polyethylene, ultra-high molecular weight polyethylene or UHMWPE, Kevlar®, Vectran®, Zylon®, polybenzobisoxazole, carbon fibers and combinations thereof. 
     According to an embodiment, said at least one tendon contact surface  18  is made of a material chosen in the group consisting of: steel, ceramic, carbide, titanium, liquid metal, and combinations thereof. 
     According to an embodiment, said at least one tendon sliding surface  66  is made of a material chosen in the group consisting of: steel, ceramic, carbide, titanium, liquid metal, and combinations thereof. 
     According to a preferred embodiment, said tendon intermediate portion  28  is made of ultra-high molecular weight polyethylene and said at least one tendon sliding surface  66  is made of steel alloy. According to a preferred embodiment, said tendon is made of ultra-high molecular weight polyethylene and said at least one tendon sliding surface  66  is made of steel. In this way, it is possible to obtain a friction coefficient in the range 0.04 to 0.08. In this way, stiction of the tendon intermediate portion  28  is avoided. 
     According to an embodiment, the dry sliding friction between said tendon sliding surface  66  and said tendon intermediate portion  28  has a friction coefficient equal to or lower than 0.1. For example, the dry sliding friction of such a tendon intermediate portion  28  over such tendon sliding surface  66  is more than five times less that the dry sliding friction defined by a metal tendon intermediate portion sliding over a metal tendon sliding surface that will result in the latter case to have a friction coefficient equal to substantially 0.5. 
     According to a preferred embodiment, said friction coefficient is lower than 0.1. 
     According to an embodiment, said total winding angle is substantially equal to 360 degrees. It is worth noting that the total friction in a tendon sliding over a tendon sliding surface over a winding angle is proportional to the tendon tension multiplied by the exponential of the product between the friction coefficient and the winding angle. Thus, a reduction of the friction coefficient allows to employ a proportionally larger winding angle. Being able to employ a larger winding cable opens up the possibility to route the tendons over the link structural bodies, avoiding the use of tendon guiding elements difficult to miniaturize. 
     According to an embodiment, the encumber of said links  6 ,  7   8  has a maximum extension, in a direction transversal to the longitudinal extension of said jointed subassembly  5  equal to or lower than 8 millimeters, and preferably equal to or lower than 5 millimeters, and preferably measuring in range from 2 millimeters to 5 millimeters. 
     According to an embodiment, said jointed subassembly  5  fits in its entirety in a cylindrical volume having a diameter measuring in range from 2 millimeters to 5 millimeters. 
     According to a preferred embodiment, said tendon intermediate portion  28  has a diameter equal to or lower than 0.5 millimeters and preferably comprised between 0.005 millimeters and 0.5 millimeters. 
     According to an embodiment, said tendon has a substantially circular cross section. According to an embodiment, the diameter of said tendon is variable in different portions of said tendon. According to an embodiment, the mechanical properties of said tendon are variable in different portions of said tendon. According to an embodiment, said tendon is obtained by joining portions of tendons with different characteristics. According to an embodiment, said tendon is connected to a stiffening rod element in the straight section running inside the shaft hollow core. According to an embodiment, said tendon is obtained by joining portions of tendons with different characteristics. 
     According to an embodiment, said at least one tendon sliding surface  66  is made of a material chosen in the group consisting of: steel, ceramic, titanium, carbide, and combinations thereof. According to an embodiment, said at least one of said structural body link is fabricated by micro injection molding. According to an embodiment, said at least one of said structural body link is fabricated by micro injection molding of liquid metal for best final dimensional tolerance, as known in the state of the art, parts below 5 mm in maximum dimension without through holes. According to an embodiment, said at least one of said structural body link is fabricated by micro injection molding of liquid metal for best mechanical performance esp. resilience and lack of fragile points. 
     According to a preferred embodiment, said tendon intermediate portion  28  is made of ultra-high molecular weight polyethylene and said at least one tendon sliding surface  66  is made of steel. According to a preferred embodiment, said tendon is made of ultra-high molecular weight polyethylene and said at least one tendon sliding surface  66  is made of steel. In this way, it is possible to obtain a friction coefficient equal to or lower than 0.04. In this way, striction of the tendon intermediate portion  28  is avoided. 
     According to an embodiment, the dry sliding friction between said tendon sliding surface  66  and said tendon intermediate portion  28  has a friction coefficient equal to or lower than 0.1. According to an embodiment, the dry sliding friction between said tendon sliding surface  66  and said tendon  19  has a friction coefficient equal to or lower than 0.1. 
     According to a preferred embodiment, said friction coefficient is lower than 0.1. 
     According to an embodiment, said total winding angle is substantially equal to 360 degrees. 
     For example, the dry sliding friction of such a tendon intermediate portion  28  over such tendon contact surface  18  is less that the dry sliding friction defined by a metal tendon intermediate portion sliding over a metal tendon sliding surface and having a total winding angle of 90 degrees, that will result in the latter case to have a friction coefficient equal to substantially 0.5. 
     According to an embodiment, the encumber of said links  6 ,  7 ,  8  has a maximum extension, in a direction transversal to the longitudinal extension of said jointed subassembly  5  equal to or lower than 8 millimeters, and preferably equal to or lower than 5 millimeters, and preferably comprised in range from 2 millimeters to 5 millimeters. 
     According to an embodiment, said jointed subassembly  5  fits in its entirety in a cylindrical volume having a diameter measuring in range from 2 millimeters to 5 millimeters. 
     According to a preferred embodiment, said tendon  19 , and preferably said tendon intermediate portion  28 , has a diameter equal to or lower than 0.5 millimeters and preferably comprised between 0.005 millimeters and 0.5 millimeters. 
     According to an embodiment, said tendon has a substantially circular cross section. According to an embodiment, the diameter of said tendon is variable in different portions of said tendon. According to an embodiment, the mechanical properties of said tendon are variable in different portions of said tendon. According to an embodiment, said tendon is obtained by joining portions of tendons with different characteristics. 
     According to an embodiment, said control unit  4  is connected to an actuator drive unit  58 , suitable for send said second command signal to said at least one actuator  25 . According to an embodiment, said at least one control unit  4  comprises a CPU. According to an embodiment, said at least one control unit  4  comprises at least one processor unit. According to an embodiment, said at least one control unit  4  provides a feedback control circuit based on the information acquired by a detection system suitable for detecting the action, for example the displacement provided and/or the force exerted by, of said at least one actuator  25 . According to an embodiment, said master tool  2  is designed to be handled by a surgeon  30 . According to an embodiment, at least a portion of said surgical instrument  70  is designed to operate on the anatomy of a patient  29 . 
     According to an embodiment, said surgical instrument  70  comprises at least one jointed subassembly  5 . 
     According to an embodiment, the term “jointed subassembly” refers to a serial sequence of links connected one to the next by joints suitable to support and/or orient and/or position and/or influence the position of an end effector of said surgical instrument  70 . According to an embodiment, from a functional point of view, said jointed subassembly can be a wrist joint, an elbow joint or a shoulder joint of a robotic or mechatronic structure. 
     According to an embodiment, said jointed subassembly  5  comprises links. 
     According to a preferred embodiment, said jointed subassembly  5  comprises at least a first link  6 , a second link  7 , and a third link  8 . In this way, said jointed subassembly  5  comprises at least three links  6 ,  7 ,  8 . 
     According to an embodiment, said first link  6  is formed of a first link structural body  9 , said first link structural body  9  being in a single piece. 
     According to a preferred embodiment, the terminology “single piece” indicates that any degree of freedom is avoided within a single link structural body, when in operative conditions. According to an embodiment, the terminology “single piece” indicates that a link structural body can comprise two or more pieces joined together in such way to avoid any degree of freedom within a single link structural body. 
     According to an embodiment, the terminology “single piece” indicates also that a link structural body can comprise two or more pieces joined together in such way that the relative spatial orientation of said two or more pieces is rigidly locked, when in operative conditions. 
     According to an embodiment, the terminology “single piece” indicates also that a link structural body is monobloc. 
     According to an embodiment, said second link  7  is formed of a second link structural body  10 , said second link structural body  10  being in a single piece. 
     According to an embodiment, said third link  8  is formed of a third link structural body  11 , said third link structural body  11  being in a single piece. 
     According to an embodiment, each link is formed of a link structural body. 
     According to an embodiment, said first link structural body  9  comprises a first link distal portion  12  forming a first joint proximal portion, and said second link structural body  10  comprises a second link proximal portion  13  forming a first joint distal portion. According to an embodiment, said first link distal portion  12  of said first link structural body  9  comprises two clevis prongs, in such way to be suitable to form a clevis joint. According to an embodiment, said second link proximal portion  13  comprises two clevis prongs, in such way to be suitable to form a clevis joint. 
     According to an embodiment, said first link distal portion  12  and said second link proximal portion  13  cooperate to form at least partially a first joint  14  providing a single degree of freedom between said first link  6  and said second link  7 . According to a preferred embodiment, said single degree of freedom between said first link  6  and said second link  7  is a roto-translational degree of freedom around a first joint axis X-X, and preferably, said roto-translational degree of freedom is a rotational degree of freedom around said first joint axis X-X. 
     According to an embodiment, said second link structural body  10  further comprises a second link distal portion  15  forming a second joint proximal portion, and said third link structural body  11  comprises a third link proximal portion  16  forming a second joint distal portion. According to an embodiment, said second link distal portion  15  comprises two clevis prongs, in such way to be suitable to form a clevis joint. According to an embodiment, said third link proximal portion  16  comprises two clevis prongs, in such way to be suitable to form a clevis joint. 
     According to an embodiment, said second link distal portion  15  and said third link proximal portion  16  cooperate to form at least partially a second joint  17  providing a single degree of freedom between said second link  7  and said third link  8 . According to a preferred embodiment, said single degree of freedom between said second link  7  and said third link  8  is a roto-translational degree of freedom around a second joint axis Y-Y, and preferably said roto-translational degree of freedom is a rotational degree of freedom around said second joint axis Y-Y. 
     According to an embodiment, said first joint  14  and said second joint  17  are each suitable for providing a single degree of freedom. 
     According to an embodiment, said first joint  14  is suitable for locking the relative movement between said first link  6  and said second link  7  in all directions except for a relative rotation around a first joint axis X-X. According to an embodiment, said second joint  17  is suitable for locking the relative movement between said second link  7  and said third link  8  in all directions except for a relative rotation around a second joint axis Y-Y. 
     According to an embodiment, said first link structural body  9 , said second link structural body  10  and said third link structural body  11  form a kinematic chain. According to an embodiment, said first link structural body  9 , said second link structural body  10  and said third link structural body  11  are directly connected in series to form a kinematic chain 
     According to an embodiment, said first link  6  is an adjacent link in respect of said second link  7 , with no intervening links in the kinematic chain. According to an embodiment, said second link  7  is an adjacent link in respect of both said first link  6  and said third link  8 . According to an embodiment, said third link  8  is an adjacent link in respect of said second link  7 . According to an embodiment, said first link structural body  9  is an adjacent link structural body in respect of said second link structural body  10 . According to an embodiment, said second link structural body  10  is an adjacent link structural body in respect of both said first link structural body  9  and said third link structural body  11 . According to an embodiment, said third link structural body  11  is an adjacent link structural body in respect of said second link structural body  10 . 
     According to an embodiment, said kinematic chain can comprises two or more branches of kinematic chain. According to an embodiment, said two or more branches extend from a single joint, for example from said second joint  17 . According to an embodiment, said two or more branches of kinematic chain share at least one link. According to an embodiment, said two or more branches of kinematic chain share at least two links out of three links of the jointed subassembly. 
     According to an embodiment, each of said first joint  14  and said second joint  17  refer to mechanical means adapted to provide a link in the kinematic chain with a rotational degree of freedom around a joint axis with respect to an adjacent link in the kinematic chain. According to an embodiment, each of said joint axis X-X, Y-Y is a common joint axis shared by two adjacent links, such that the two adjacent links can rotate one with respect to the other around said common joint axis. According to an embodiment, said first joint  14  defines a first joint axis X-X, wherein said first joint axis X-X is a common joint axis shared by both said first link  6  and said second link  7 , such that the two adjacent links can rotate one with respect to the other around said common joint axis. According to an embodiment, said second joint  17  defines a second joint axis Y-Y, wherein said second joint axis Y-Y is a common joint axis shared by both said second link  7  and said third link  8 , such that the two adjacent links can rotate one with respect to the other around said common joint axis 
     According to an embodiment, a kinematic chain formed by said at least three links  6 ,  7 ,  8  have two degrees of freedom. 
     According to an embodiment, a kinematic chain formed by said at least three links  6 ,  7 ,  8  have exactly two degrees of freedom. In other words, according to an embodiment, the total number of degrees of freedom of a kinematic chain formed by said at least three links  6 ,  7 ,  8  is two. According to an embodiment, a kinematic chain formed by said first link  6 , said second link  7  and said third link  8  have exactly two degrees of freedom. In other words, according to an embodiment, the total number of degrees of freedom of a kinematic chain formed by said first link  6 , said second link  7  and said third link  8  is two. 
     According to an embodiment, said jointed subassembly  5  avoids to comprise actuators. According to an embodiment, said jointed subassembly  5  avoids to comprise actuators within said kinematic chain. According to an embodiment, no actuators are provided among said links. 
     According to an embodiment, at least two among said first link structural body  9 , said second link structural body  10  and said third link structural body  11  comprise at least one tendon sliding surface  66 , avoiding that said at least one tendon sliding surface  66  is a hole surface. In other words, said at least one tendon contact surface  18  avoids to delimit a through hole in a link structural body  9  or  10  or  11 . According to an embodiment, a normal line, or orthogonal line, to said at least one tendon sliding surface  66  avoids to intersect the structural body comprising said at least one tendon sliding surface  1866  According to an embodiment, said tendon sliding surface  66  avoids to face itself. 
     According to an embodiment, said tendon contact surface  18  urges said tendon intermediate portion  28  away from the link structural body comprising said tendon sliding surface  66 . 
     According to an embodiment, said tendon contact surface  18  embraces one of said tendon over an angle equal to or lower than 180 degrees. According to an embodiment, said tendon contact surface  18  is an outer surface of one of said link structural bodies  9 ,  10 ,  11 . According to an embodiment, said tendon contact surface  18  delimits at least partially the encumber of one of said link structural bodies  9 ,  10 ,  11 .According to an embodiment, each tendon comprises a first longitudinal side and a second opposite longitudinal side, wherein one between said first longitudinal side and said second longitudinal side is in contact with at least one of said links. In other words, when said first longitudinal side is in contact with a given link, said first longitudinal side faces away from said given link. According to an embodiment, each of said first longitudinal side and said second opposite longitudinal side covers on said tendon an angle of substantially  180  while remaining disjointed one another. 
     According to an embodiment, said surgical instrument  70  comprises tendons  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  31 ,  32 . According to an embodiment, said tendons acts as actuation cables suitable for working only in traction. 
     According to an embodiment, said surgical instrument  70  comprises at least three tendons. Each tendon of said at least three tendons comprises a tendon proximal portion  26 , associated to said at least one actuator  25 , a tendon distal portion  27 , secured to said second link  7  or to said third link  8 , a tendon intermediate portion  28 , extending between said tendon proximal portion  26  and said tendon distal portion  27 . 
     According to an embodiment, said surgical instrument  70  comprises a further tendon so as to comprise at least four tendons, wherein said at least one intermediate portion  28  of each of said at least four tendons contacts said jointed subassembly  5  only in said at least one tendon sliding surface  66 . 
     According to an embodiment, a pair of tendons have their tendon distal portions  27  secured to a same link, so as to work as. In other words, a pair of tendons are secured to a same link so as to work as antagonist tendons. According to an embodiment, a pair of tendons share their tendon distal portions  27 , so as to work as antagonist tendons. According to an embodiment, a pair of tendons working as antagonist tendons are in single piece. According to an embodiment, said tendons  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  31 ,  32  comprises a first pair of tendons  19 ,  20 , suitable to work as antagonist tendons. According to an embodiment, said tendons  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  31 ,  32  comprises a second pair of tendons  21 ,  22 , suitable to work as antagonist tendons. 
     According to an embodiment, a pair of tendons have their tendon distal portions  27  secured to a same link, so as to work as one tendon. In other words, a pair of tendons are secured to a same link so as to work in parallel as a single tendon. According to an embodiment, a pair of tendons share their tendon distal portions  27 , so as to work in parallel as a single tendon. According to an embodiment, a pair of tendons working as a single tendon are in single piece. According to an embodiment, said tendons  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  31 ,  32  comprises a first pair of tendons  19 ,  20 , suitable to work as a single tendon. According to an embodiment, said tendons  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  31 ,  32  comprises a second pair of tendons  21 ,  22 , suitable to work as a single tendon. According to an embodiment, said tendons  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  31 ,  32  comprises a third pair of tendons  23 ,  24 , suitable to work as antagonist tendons. According to an embodiment, said tendons  19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  31 ,  32  comprises a fourth pair of tendons  31 ,  32  suitable to work as antagonist tendons. 
     According to an embodiment, at least one between said second link  7  and to said third link  8  comprises at least a tendon securing portion  49 , suitable to receive said tendon distal portion  27 . According to an embodiment, at least one between said second link  7  and to said third link  8  comprises two tendon securing portions  49 , suitable to receive said tendon distal portion  27  of two tendons working as antagonist tendons. For example, as shown in  FIG. 35 , said tendons  19  and  20  works in parallel as a single tendon. 
     According to an embodiment, said tendon intermediate portion  28  of each tendon contacts said jointed subassembly  5  exclusively in said at least one tendon sliding surface  66  of at least two among said first link structural body  9 , said second link structural body  10  and said third link structural body  11 . This avoids the need of any additional parts for routing the tendons and minimizes parts count and difficulty of assembly. This also avoids unnecessary friction and wear of tendons from further contact with the jointed assembly. 
     According to a preferred embodiment, this avoids that said tendon intermediate portion  28  of each tendon contacts any other portions of said jointed subassembly  5 . According to an embodiment, said tendon intermediate portion  28  of each tendon contacts said jointed subassembly only in said at least one tendon sliding surface  66 . 
     Advantageously, thanks to the characteristics of surgical instrument  70 , it is possible to miniaturize the dimensions of said jointed subassembly  5 . 
     According to an embodiment, each of said first link structural body  9 , said second link structural body  10  and said third link structural body  11  comprise at least one tendon contact surface  18 . 
     According to an embodiment, said at least one tendon sliding surface  66  is a groove surface. In other words, said tendon sliding surface, according to an embodiment, delimits at least partially a groove made in at least one link. 
     According to an embodiment, at least one link structural body of said link structural bodies can be associated to appendices in separate pieces with respect of said link structural body, such as pulleys, for example idle pulleys, i.e., pulleys rotatably connected to the link, but said appendices avoid to provide a contact surface for any one of said tendon intermediate portions  28 . 
     According to an embodiment, said first link distal portion  12  and said second link proximal portion  13  cooperate in a geometric coupling, to form said first joint  14 . According to an embodiment, said second link distal portion  15  and said a third link proximal portion  16  cooperate in a geometric coupling, to form said second joint  17 . 
     According to an embodiment, at least one between said first joint  14  and said second joint  17  is a pivot joint. According to an embodiment, said pivot joint is a rotational joint which provides a mechanical pivot for the joint axis X-X or Y-Y. 
     According to an embodiment, at least one between said first joint  14  and said second joint  17  is a rolling joint. According to one embodiment, said rolling joint provides a rolling contact between a link structural body of a link and a link structural body of an adjacent link, over respective rolling surfaces such that the rolling motions happens around a fixed joint axis X-X or Y-Y. 
     According to an embodiment, at least one between said first joint  14  and said second joint  17  is a pin joint. 
     According to an embodiment, said pin joint comprises at least one pin  33  and at least one pin seat  34 , suitable to receive said at least one pin  33 . According to an embodiment, said pin  33  as a prevailing longitudinal development. 
     According to an embodiment, said at least one pin  33  is of smaller diameter that said at least one pin seat  34  receiving said at least one pin  33 , so that a clearance results in the coupling of said pin  33  and said pin seat  34 . 
     According to an embodiment, said pin seat  34  is a pass-through hole, delimited by at least one of said link structural bodies  9 ,  10 ,  11 . 
     According to an embodiment, said pin seat  34  is a cavity, delimited by at least one of said link structural bodies  9 ,  10 ,  11 . 
     According to an embodiment, said pin seat  34  is a cavity, having a cavity mouth  40  narrower than said at least one pin  33  and said cavity mouth  40  is unsuitable for receiving said pin  33 . Such a cavity prevents the pin  33  from exiting the pin seat  34  in a direction transversal to the longitudinal development of said pin  33 . 
     According to an embodiment, said pin seat  34  is delimited by a pin seat boundary  35  facing said pin seat  34 . Preferably, said pin seat boundary  35  is suitable for facing a pin  33  received in said pin seat  34 . 
     According to an embodiment at least one among said first link distal portion  12  of said first link structural body  9 , said second link proximal portion  13  of said second link structural body  10 , said second link distal portion  15  of said second link structural body  10 , and said third link proximal portion  16  of said third link structural body  11 , comprises said pin seat boundary  35  which delimits said pin seat  34  for receiving a pin  33 . 
     According to an embodiment, said pin seat boundary  35  is substantially circular. According to an embodiment, said pin seat boundary  35  comprises an arch of a circumference. According to an embodiment, said pin seat boundary  35  describes a paraboloid profile. According to an embodiment, said pin seat boundary  35  describes a cam profile, suitable for cooperating with said pin  33  to form a cam-follower mechanism. 
     According to an embodiment, at least one between said first joint  14  and said second joint  17  is a cam joint. 
     According to an embodiment, at least one between said first joint  14  and said second joint  17  is a clevis joint. According to an embodiment, said clevis joint is formed by two clevis prongs  50  of a link structural body of a link which embraces a portion, and preferably a cylindrical mating portion, of a link structural body of an adjacent link. 
     According to an embodiment, said pin  33  is realized in separate piece in respect of said first link  6  and said second link  7  and associated to at least two pin seats  34 , delimited by said first link distal portion  12  and said second link proximal portion  13 , respectively, to form said first joint  14 . 
     According to an embodiment, said pin  33  is realized in separate piece in respect of said second link  7  and said third link  8  and associated to at least two pin seats  34 , delimited by said second link distal portion  15  and said third link proximal portion  16 , respectively, to form said second joint  17 . 
     According to an embodiment, said pin  33  is in single piece with a link  6  or  7  or  8 . 
     According to an embodiment, said pin  33  is in single piece with a link structural body  9  or  10  or  11 . 
     According to an embodiment, said at least one pin  33  is in single piece with said first link structural body  9  and projects cantilevered from said first link distal portion  12 . According to an embodiment, said at least one pin  33  is in single piece with said second link structural body  10  and projects cantilevered from said second link proximal portion  13 . According to an embodiment, said at least one pin  33  is in single piece with said second link structural body  10  and projects cantilevered from said second link distal portion  15 . According to an embodiment, said at least one pin  33  is in single piece with said third link structural body  11  and projects cantilevered from said third link proximal portion  16 . 
     According to an embodiment, for example shown in  FIG. 19 , at least one between said first joint and said second joint is a double-joined joint  36 . Thanks to such double-joined joint  36  is possible to provide a single degree of freedom between two adjacent links, ad detailed described in prior art document U.S. Pat. No. 5,710,870. According to an embodiment, said double-joined joint  36  comprises at least a hinge strut  37  connected to two of said link structural bodies. According to a preferred embodiment, said double-joined joint  36  comprises two opposite hinge struts  37 . 
     According to one embodiment, said double-joined joint  36  is formed by a link and an adjacent link attached to each other via a pair of hinged struts  37 . According to one embodiment, said link and said adjacent link pivot about first pivot axis and second pivot axis, wherein a constraining component constrains said link and said adjacent link to rotate with respect to each other. For example, said constraining component can be fixed spurs gears which mesh together or actuation cables routed appropriately. According to an embodiment, said constraining component is said at least one hinged strut  37 . 
     According to an embodiment, as shown for example in  FIGS. 24 and 25 , at least one between said first joint  14  and said second joint  17  is formed by opposite joint portions that intermesh one another. According to an embodiment, said first link distal portion  12  delimits at least a joint proximal groove  38  and said first link distal portion  13  comprises at least a joint distal tooth  39 , said joint distal tooth  39  cooperates with said joint proximal groove  38  to form said first joint  14 . According to an embodiment, said second link distal portion  15  delimits at least a joint proximal groove  38  and said second link distal portion  16  comprises at least a joint distal tooth  39 , said joint distal tooth  39  cooperates with said joint proximal groove  38  to form said second joint  17 . According to an embodiment, both said joint proximal groove  38  and said joint distal tooth  39  extends substantially parallel to a joint axis. 
     According to an embodiment, at least one of said links, preferably said third link  8 , comprises a C-holder portion  41 , suitable for receiving a terminal element  42 . For example, said terminal element  42  can be a laser fiber, an irrigation tube, a suction tube or a tissue sensing probe. 
     According to an embodiment, said jointed subassembly  5  forms at least a portion of an end effector of said surgical instrument  70 . 
     According to an embodiment, said jointed subassembly  5  is a wrist subassembly, wherein said first joint  14  is substantially orthogonal to said second joint  17 . According to an embodiment, said jointed subassembly  5  is a wrist subassembly wherein said first joint axis X-X is substantially orthogonal to said second joint axis Y-Y. 
     According to an embodiment, said jointed subassembly  5  is an elbow subassembly, wherein said first joint  14  is substantially parallel to said second joint  17 . According to an embodiment, said jointed subassembly  5  is an elbow subassembly, wherein said first joint axis X-X is substantially parallel to said second joint axis Y-Y. 
     According to an embodiment, said jointed subassembly  5  comprises a further third link  43  formed of a further third link structural body  44 , said further third link structural body  44  being in a single piece. 
     According to an embodiment, said further third link structural body  44  of said further third link  43  comprises a further third link joint portion  45 , said further third link joint portion  45  cooperates with said second link distal portion  15  of said second link structural body  10  of said second link  7  to form a portion of said second joint  17  providing a single degree of freedom between said second link  7  and said further third link  43 . In this way, said second joint  17  provides a single degree of freedom between said second link  7  and said third link  8 , a single degree of freedom between said second link and said further third link  43 , and as a result a single degree of freedom between said third link  8  and said further third link  43 . 
     According to an embodiment, said third link  8  forms a first branch of said kinematic chain and said further third link  43  forms a second a branch of said kinematic chain, wherein said first branch and said second branch are joined in said second joint  17 . In this way said kinematic chain is a branched kinematic chain. 
     According to an embodiment, said third link  8  and said further third link  43  form an instrument tip  46  of said surgical instrument  70 . According to an embodiment, said instrument tip  46  has an internal degree of freedom of grasp. According to an embodiment, said instrument tip  46  has at least one yaw degree of freedom in respect of said second link  7 . 
     According to an embodiment, said jointed subassembly  5  comprises at least an additional link  47 . According to an embodiment, said at least one additional link  47  is formed of an additional link structural body  48 . According to an embodiment, said additional link structural body  48  is jointed to an adjacent link forming an additional joint. For example, said additional link structural body  48  can form an additional joint with a portion of said third link structural body  11 . According to an embodiment, said additional link structural body  48  is jointed to an adjacent yet additional link structural body to form a joint. 
     According to an embodiment, said at least one tendon contact surface  18  is a ruled surface formed by a plurality of straight lines. According to an embodiment, each tendon contact surface  18  is a ruled surface formed by a plurality of straight lines. According to an embodiment, said plurality of straight lines are all parallel to a joint axis X-X or Y-Y. Preferably, said plurality of straight lines are all parallel to the joint axis X-X or Y-Y located closer to said at least one tendon contact surface  18 . 
     According to an embodiment, said at least one tendon contact surface  18  is a convex surface. 
     According to an embodiment, at least one link structural body among said first structural body  9 , said second structural body  10  and said third structural body  11  comprises more than one tendon contact surface  18 . 
     According to an embodiment, all said more than one tendon contact surface  18  are convex surfaces defining with their prolongations thereof a single convex volume. According to an embodiment, the wording “convex volume” means that given a pair of points chosen inside said convex volume, the shorter straight conjunction between them is inside the convex volume in its entirety. This avoids providing grooves or channels on pulleys for guiding the tendons, allowing to further miniaturize the dimensions of the link structural bodies and of the jointed subassembly  5 . According to an embodiment, all said more than one tendon contact surfaces  18  of said link structural body of at least one of said links define with their prolongations thereof a link convex hull of said link structural body. According to an embodiment, said link convex hull is defined as the volume comprised within a film wrapping one of said link. 
     According to an embodiment, said surgical instrument  70  comprises a shaft  51 . 
     According to a preferred embodiment, said first link  6  is directly connected to said shaft  51 . 
     According to an embodiment, said surgical instrument  70  comprises at least a frame  52 , suitable for being detachably connected to a portion of said slave manipulator  3 . According to an embodiment, said surgical instrument  70  comprises at least a frame  52 , suitable for being detachably connected to an actuator compartment of said slave manipulator  3 , said actuator compartment hosting said at least one actuator  25  defining a motor compartment  69  or motor box  69 . According to an embodiment, said at least one actuator  25  is housed within a portion of said slave manipulator  3 . 
     According to an embodiment, said surgical instrument  70  is detachably associated to said slave manipulator  3 . 
     According to an embodiment, said surgical instrument  70  is associated in a reversible manner to said slave manipulator  3 . 
     According to an embodiment, said shaft  51  extends between said frame  52  and said jointed assembly  5 . 
     According to an embodiment, said shaft  51  is a rigid shaft. According to an embodiment, said shaft  51  has a hollow core that allows the passing of the tendons. 
     According to an embodiment, said shaft  51  is a flexible shaft. According to an embodiment, said shaft  51  comprises channels to guide at least one of said tendons. 
     According to an embodiment, said shaft  51  is proximally connected to said frame  52  and distally connected to said first link  6  of said jointed subassembly  5 , forming a tubular element connection  61 . According to an embodiment, said tubular element connection  61  is a rigid connection, avoiding to provide any degree of freedom between said shaft  51  and said first link  6 . According to an embodiment, said tubular element connection  61  comprises at least two tubular element pins  62  inserted in tubular element pin seats  63 , preferably holes. Preferably, said tubular element pin seats  63  are at least in number of two, for providing a rigid connection. According to an embodiment, said shaft is distally connected to said first link  6  and the connection includes a solder. 
     According to an embodiment, said shaft  51  defines a longitudinal shaft axis r-r, substantially coincident to the axis of longitudinal development of said shaft  51 . According to an embodiment, said shaft  51  is suitable to rotate around said longitudinal shaft axis r-r to provide a roll motion to the jointed subassembly, in such way to provide said jointed subassembly  5  of a further degree of freedom of roll around said longitudinal shaft axis r-r. 
     According to an embodiment, said first link structural body  9 , said second link structural body  10  and said third link structural body  11  each comprising a passing-through payload hole, and wherein all said passing-through payload holes are substantially aligned one another in such way to be suitable for receive a single payload element  64 , preferably extending substantially along said kinematic chain. According to an embodiment, said payload element  64  is one of an irrigation tube, a laser fiber, a cautery wire, a pair of cautery wires, a bending sensing element, avoiding that said payload element  64  is a tendon and/or works as an actuation cable. 
     According to an embodiment, said tendon distal portion  27  comprises a boss. According to an embodiment, said tendon distal portion  27  comprises a loop. According to an embodiment, said tendon distal portion  27  comprises a knot. According to an embodiment, said tendon distal portion  27  comprises a portion which is glued to a portion of said jointed subassembly  5 . According to an embodiment, said tendon distal portion  27  comprises a portion which is wrapped around a portion of a link  6 ,  7 ,  8  multiple times. According to an embodiment, said portion which is wrapped around with a curvature radius that is substantially equal to the diameter of the tendon. 
     According to an embodiment, said tendon proximal portion  26  is glued to a portion of said frame  52 . According to an embodiment, said tendon is unraveled into strands around its first tendon proximal portion  26  such as to maximize the glued surface. 
     According to an embodiment, at least one of said tendons, and preferably each tendon of said tendons, is exclusively suitable to work under tensile load applied at the tendon proximal portion  26  and at the tendon distal portion  27 , avoiding said tendon to be pinched, to be laterally guided in a channel or to comprise a sheath. 
     According to an embodiment, at least one of said tendons, and preferably each tendon of said tendons, is suitable to be pre-lengthened with a load cycle comprising at least two loads of an entity equal to at least half of the tensile breaking strength of said tendon. 
     According to an embodiment, said slave manipulator  3  comprises at least a micromanipulator, suitable for providing said surgical instrument  70  with three Cartesian degrees of freedom. 
     According to an embodiment, said at least one actuator  25  comprises at least a pushing element  53  and said surgical instrument  70  comprises, in its proximal frame  52 , at least a plunger  54  associated to a tendon, wherein, whenever said surgical instrument  70  is connected with said slave manipulator  3 , said pushing element  53  is suitable for pushing against said plunger  54  to determine that the plunger  54  deflects the tendon proximal portion  26  of the tendon associated thereto and to obtain a movement of a link associated to the tendon distal portion of said tendon. 
     According to an embodiment, a sterile barrier  55  is interposed between said slave manipulator  3  and said surgical instrument  70 . According to an embodiment, a sterile barrier  55  is interposed between said at least one pushing element  53  of said slave manipulator  3  and said at least one plunger  54  of said surgical instrument  70 . According to an embodiment, said at least one plunger is associated to an elastic element  56  suitable for biasing the plunger against said tendon proximal portion  26  associated thereto. According to an embodiment, said plunger  54  comprises a tendon contact portion  57  which contacts said tendon proximal portion  26 . According to an embodiment, said tendon contact portion  57  of said plunger  54  comprises a guide pulley. According to an embodiment, said tendon proximal portion  26  is guided by a plurality of pulleys. 
     According to a general embodiment, it is provided a surgical instrument  70  according to any one of the embodiments previously described. 
     According to a general embodiment, it is provided a slave assembly comprising at least a slave manipulator  3  according to any one of the embodiments previously described and at least a surgical instrument  70  according to any one of the embodiments previously described. 
     By virtue of the features described above, provided either separately or in combination, where applicable, in particular embodiments, it is possible to satisfy the sometimes contrasting needs disclosed above, and to obtain the aforesaid advantages, and in particular: 
     it is provided a miniaturization of slave surgical instrument; 
     an extreme miniaturization below  5  mm of transversal diameter of the jointed subassembly can be achieved, without employing idle pulleys, and without employing hole or guide channels that pass through any of the structural bodies of the three links; 
     it is achieved that the tendons that slide over the structural body of an intermediate link to actuate a more distal link and wrap around the intermediate link structural body by 90 degrees already when the jointed subassembly, for example a wrist subassembly, is in its straight configuration, and while this is taught against by prior art due to the increase of sliding friction that it produces, in some embodiments disclosed above, the 90 degrees wrap allows to slide the tendons on the outer surfaces of the links, rather than passing them through holes or channels, in order to constrain the tendons to stay within the diameter of the link when the distal links are bent; 
     the tendons can lay in equilibrium on said outer surfaces of the links, finding their minimum energy path resulting from their tension and the surface friction forces, avoiding altogether sharp bends, and in this way, it is enabled the use of polymeric tendons, such a polyethylene, UHMWPE that are known to be stronger than steel and with much lower friction over metallic substrate, such as steel, for the tendon material or outer material, as said polymeric tendons made in polyethylene or UHMWPE, unlike steel tendons or other polymeric tendons, suffer abrasion caused by sliding over sharp edges or side walls, and therefore a design that routes the tendons over the outer surfaces of the links laying them in equilibrium on said outer surfaces allows the polymeric tendon to flatten on said outer surface and minimize its abrasion; 
     the total friction between the tendon and the links can be greatly reduced rather than increased, because the increase in larger winding angle or wrap angle in the capstan equation (by 90 degrees, equal to approx. 1.5 radians) is effectively countered by a reduction of the friction coefficient from 0.5 of steel cables over steel to 0.04 to 0.08 for polyethylene over steel alloys. 
     Those skilled in art may make many changes and adaptations to the embodiments described above or may replace elements with others which are functionally equivalent in order to satisfy contingent needs without however departing from the scope of the appended claims. 
     LIST OF REFERENCES 
     
         
           1  Robotic microsurgery assembly 
           2  Master tool 
           3  Slave or slave manipulator 
           4  Control unit 
           5  Jointed subassembly 
           6  First link 
           7  Second link 
           8  Third link 
           9  First link structural body or structural body of said first link 
           10  Second link structural body or structural body of said second link 
           11  Third link structural body or structural body of said 
           12  First link distal portion of said first link structural body 
           13  Second link proximal portion of said second link structural body 
           14  First joint 
           15  Second link distal portion of said second link structural body 
           16  Third link proximal portion of said third link structural body 
           17  Second joint 
           18  Tendon contact surface 
           19 ,  20 ,  21 ,  22 ,  23 ,  24 ,  30 ,  31  Tendons 
           25  Actuator 
           26  Tendon proximal portion 
           27  Tendon distal portion 
           28  Tendon intermediate portion 
           29  Patient 
           30  Surgeon 
           33  Pin 
           34  Pin seat 
           35  Pin seat boundary 
           36  Double-joined joint 
           37  Hinge strut 
           38  Joint proximal groove 
           39  Joint distal tooth 
           40  Cavity mouth 
           41  c-holder portion 
           42  Terminal element 
           43  Further third link 
           44  Further third link structural body 
           45  Further third link joint portion 
           46  Instrument tip 
           47  Additional link 
           48  Additional link structural body 
           49  Tendon securing portion 
           50  Clevis prong 
           51  Shaft 
           52  Frame 
           53  Pushing element 
           54  Plunger 
           55  Sterile barrier 
           56  Elastic element 
           57  Tendon contact portion of the plunger 
           58  Actuator drive unit 
           59  First command signal 
           60  Second command signal 
           61  Tubular element connection 
           62  Tubular element pin 
           63  Tubular element pin seat 
           64  Payload element 
           65  Sliding path 
           66  Tendon sliding surface 
           67  Proximal contact surface border 
           68  Distal contacxt surface border 
           69  Motor box or motor compartment 
           70  Medical Instrument or Surgical Instrument or Instrument 
         X-X First joint axis 
         Y-Y Second joint axis 
         r-r Longitudinal direction of the shaft 
         T-T Tendon longitudinal path 
         α Local winding angle or first local winding angle 
         ß Local winding angle or second local winding angle 
         α+ß Total winding angle