The da Vinci® system: technology and surgical analysis

  • Contents

  • The main parts of the da Vinci® 66

  • Slave design® 67

  • The master control 70

  • The control unit and motion mapping between master and slave 71

  • Force and haptic feedbacks 73

  • Dual master control and simulator 73

  • Technical critical analysis 73

  • Surgical critical analysis 74

The aim of this chapter is to provide some details about the technology involved in the da Vinci® surgical manipulator system. It does not claim either to be a user manual, or to provide a complete description of its technology. Our aim is limited to provide some basic information about the only commercially available ENT surgical robot, as an introduction to the later chapters which focus on its ENT clinical applications and related results. For an explanation of less common technical terms, please refer to chapter 4 .

Originally, the da Vinci® robotic system was developed by SRI, a non-profit research institute, later funded by the US Army (DARPA 1

1. DARPA (Defense Advanced Research Agency) is also the shell in which ARPANET (the first internet) started.

) in 1985 with the aim of performing telesurgery on injured soldiers when surgeons could be located far away from the advanced medical facilities near the front line. NASA subsequently joined the project leading to an even more ambitious program to perform surgery in space with surgeons located on Earth. Ten years later, the program was stopped because it was deemed to be unachievable with the technology available at the time. A number of Stanford engineers who had worked on the project decided to launch a start-up to redirect the project toward the more realistic goal of performing robotically assisted laparoscopic surgery. In 1995, Intuitive Surgical was created and acquired the patent portfolio of SRI. The company then grew by developing an aggressive market control strategy, acquiring any significant companies working in the same field, such as Computer Motion.

Marketed for the first time in Europe on 1999, the da Vinci® robot has been improved over time: in 2003 a fourth arm to hold an endoscope was introduced. The S version was then released in 2006, offering true 3D vision with improved working volume. In 2009, the da Vinci® Si version added a second master station, allowing two surgeons to work in collaboration. Finally, the Xi version, available since April 2014, has a more compact design, improving working volume, with the added capability to have an endoscopic camera attached to any of the four arms and the future capability to work with the Intuitive Surgical proprietary fluorescence imaging system [ ].

Although there are some differences between the different versions of the da Vinci® system, none of these are very significant and we shall consider them as a whole.

The main parts of the da Vinci®

Despite its common name, the da Vinci® system is not in fact a robot but a master-slave telemanipulator. Essentially, it is made of three major components ( Figure 6.1 ): a slave station incorporating four independent arms, a console for the master control with two independent arms which can be smoothly manipulated by the surgeon, and a control unit consisting of a power supply, a computer, a 3D image processor and a monopolar diathermy circuitry. End-effector instruments are secured onto three of the four slave arms, most of these relying on extensively patented technology, trading under the name Endowrist®. A second master-control console is available as an option ( Si ® version), thus permitting dual-surgeon four-hand procedures.

Figure 6.1

The da Vinci® system general structure.

The slave manipulator (1), master-control console (2), control-unit (3). Optionally, a second master-control (4) allows dual-surgeon-four-hand procedures.

(Source: courtesy of Intuitive Surgical Inc.)

Slave design®

Passive arms®

The slave part is a massive structure made of four arms. The kinematics of each single arm mostly use serial linkages and rely on the concept of the remote center of motion (RCM) [ ]. A passive proximal part, dedicated to set-up the RCM point of each arm, is built from four joints ( Figure 6.2 ). The first joint is prismatic and allows adjustment of height. This is followed by three planar revolute joints of the SCARA type, thus allowing easy passive manipulation. The prismatic joint is electrically actuated while the other joints only contain brakes with a push-button to release the brakes during the set-up process.

Figure 6.2

Da Vinci® system with its first 4 DOF.

Prismatic joint J 1 is electrically actuated, allowing adjustment of the arm to the correct level with respect to the patient’s height. Joints J 2 , J 3 , J 4 form a SCARA (please refer to “Kinematic structures”, chapter 4 ) passive arm with strong brakes to block them once the arm is correctly positioned.

(Source: Bertrand Lombard.)

The bulky system base is sufficiently heavy to make the whole system immobile once the roller brakes are engaged, and the system is therefore not mechanically secured to the operating table. The latest versions of the system are motorized in order to assist the nurse, who may not have the necessary strength to set-up the system.

Actuated arms

The structure of these arms may be broken down into two sub-units: the manipulator arms with 3 active degrees of freedom (DOF) and the end-effector instrument, which is actively actuated with 3 further DOF, together with an optional grip function, depending the instrument used.

The manipulator active arm is the result of long research [ ] and combine serial linkages with a parallelogram parallel structure used for the RCM ( Figure 6.3 ).

Figure 6.3

The da Vinci® system main structure.

Revolute actuated joints J 4 , J 5 share the same axis Pa , while passive J 6 , J 7 revolute joints replicate J 5 angular motion to the instrument holder. Thus, J 5 acts exactly as if it were located at RCM point. J 8 is a prismatic joint ensuring translation centered on the RCM point. Prismatic joint J 8 is made of multiple superposed sliders actuated via cable and pulleys. Finally, the da Vinci® main structure is composed of three active joints: instrument axial translation, and two orthogonal rotations around the patient’s entry point RCM.

(Source: Bertrand Lombard, based on Intuitive Surgical patent n° 8613230.)

Initially the RCM was built around rigid linkages but has evolved into a cable-driven remote control of motion in order to make each arm lighter and more compact ( Figures 6.4 and 6.5 ).

Figure 6.4

The da Vinci® system: details of the RCM mechanism.

J 6 passive pulled is cable-driven (pink) from motorized joint J 5 . In turn, J 6 moves the link j 67 and transmits its motion via a cable (yellow) to J 7 pulley, itself connected to the instrument holder. This mechanism allows J 7 to be provided with the same amount of angular motion as J 5 while keeping the actuator away from the patient. The whole system behaves like a parallelogram (green dotted lines) which is angular conservative.

(Source: Bertrand Lombard, based on Intuitive Surgical patent n° wo2006039092.)

Figure 6.5

Inside a da Vinci® arm.

View of the RCM mechanism integrated in an arm. Prismatic sliders located on the column and cables and pulleys in the arm (ensuring RCM motion) are clearly visible.

(Source: courtesy of Intuitive Surgical.)

EndoWrist® instruments

These form the terminal part of the telemanipulator system and are probably the most imaginative contribution of the whole da Vinci® system to surgery. They also represent the most important part of the Intuitive Surgical Inc. patent portfolio with more than 200 related patents.

EndoWrist® includes a range of instruments with various mechanisms ( Figure 6.6 ). Our aim is limited to a kinematic analysis of forceps which are the most mechanically sophisticated item and the most important in transoral robotic surgery.

Figure 6.6

A few parts of the EndoWrist® instrument range.

(Source: courtesy of Intuitive Surgical.)

EndoWrist® forceps have been designed to enable the kinematic system to work within the body. This ingenious yet sophisticated concept provides exceptional dexterity which is unachievable with conventional instrumentation. Three DOF plus the forceps jaws opening-closing actuation are operated by tendon-driven mechanisms.

EndoWrist® instruments are available with 8 and 5 mm output diameters, a total length of 57 cm and a usable length of up to 38 cm [ ]. Eight millimeters instruments have cardan joints while 5 mm ones have a more sophisticated articulated structure [ ] formed from four serial joints ( Figure 6.7 ).

Figure 6.7

Internal design of EndoWrist® instrumentation.

(Source: Bertrand Lombard, partly based on Intuitive Surgical patent n° US 8398634.)

The 5 mm instruments are the most commonly used for transoral robotic surgery due to the limited space available in the oropharyngeal cavity.

This four vertebral joints tip structure allows the joint diameters to be reduced, at the cost of increased length: craniocaudal Φ and lateral rotations θ are each uncoupled in two alternating rotation stages, Φ 1 , θ 1 , Φ 2 , θ 2 , respectively. Cables and pulleys are used to control joint angles and grip function (forceps jaws opening-closure). The system use an agonist-antagonist control scheme which therefore requires two actuating cables by DOF. Subsequently, 6 ropes are required in order to actuate craniocaudal and lateral rotations and the forceps jaws. The path of these cables runs inside the instrument shaft with spacers to avoid cable conflict and the resulting friction. The 4 th DOF is the shaft rotation Ψ , which is operated directly inside the actuation box. Four capstans are each dedicated to a DOF, while tensioning pulleys ensure constant cable tensions which otherwise would deteriorate as a result of ambient temperature, wear, and repeated sterilizations.

Each capstan itself is mechanically connected to a rotating drum when the EndoWrist® instrument is fixed onto a manipulator arm. Another set of cables provides motion for these drums and consequently, actuation of the 4 DOF of the forceps.

Kinematically, this configuration is of the serial kind, allowing a large range of motions with a very limited end-effector footprint. Forceps full angulation, Φ and θ is ± 90°, while Ψ allows full 360° axial rotation, providing very comfortable reach. Payload capabilities are roughly of the same order of those which are usual in open surgery, although there is no accurate information on this feature.

The drawback of 5 mm articulated instrumentation is that biplanar vertebral continuum joints have a greater radius of curvature and therefore require more space to make them angulated than cardan-jointed 8 mm instruments.

Due to its complex and therefore expensive factoring process and the relative weakness of EndoWrist® architecture, the manufacturer has compromised in order to comply with these contradictory statements. The system is sold to be used 5 or 10 times [ ] (depending the instrument) before being discarded. It introduces a new concept in the history of medical devices: the middle-consumable instrument. An electronic chip with a thermistor which is incorporated into the control box memorizes each sterilization before destroying an identifier code, obliging the user to discard the instrument once its maximum number of cycles has been reached.

3D endoscopes

These are made of two Hopkin’s type endoscopes juxtapositioned with a light channel in a single tube ( Figure 6.8 ). Each endoscope is 6 mm apart the other allowing the true retinal disparity required for stereoscopic vision. Two outer diameters are available: 8.5 and 12 mm. Normally only the first type is used in ENT-HNS surgery.

Jun 9, 2019 | Posted by in OPHTHALMOLOGY | Comments Off on The da Vinci® system: technology and surgical analysis
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