Surgical robots at work

Master-slave manipulators

These currently constitute the main class of surgical robot. The surgeon is the driver of a master control made of electromechanical arms. The surgeon's manipulations are transformed into position/orientation values by encoders and are sent to a computer software, running the inverse kinematics of the electromechanical arms. The surgeon's gesture is therefore converted into a numerical pose, usually a matrix containing rotation orientations and Cartesian coordinates.

These numeric data are then processed before being sent to the slave, made of manipulators which replicate surgeon's hands motion ( Figure 5.1 ). It can be made with more arms than a surgeon has, typically 1 to 4.

The da Vinci® system from Intuitive Surgical Corp., described in chapter 6 , is a typical example of a telemanipulator. Strictly speaking, telemanipulators are not robots since they cannot be programmed to perform a surgical task independently, but rather only replicate surgeon's hand motions. Their main goal is to improve surgeon dexterity, both by using specific instruments (with specifically designed degrees of freedom [DOF]) fixed to slave arms and by scaling and filtering surgeon's hands motion, to allow micromovements and reduce tremor respectively.

Additional features such as haptic control can be implemented on them, but most systems rely mainly on the surgeon's visiomotor loop, namely the eye-hand coordination. For this reason, a good imaging system with high resolution and frame rate is mandatory to provide good immersion of the surgeon in the operating field [ ]. In turn, good immersion significantly improves surgeons' performances [ ], which is an added advantage of telemanipulators. Another significant advantage is the possibility of providing mentoring from one skilled surgeon to one in training, both working on two networked master control stations, with the advantage that they are equally immersed in the same operating field.

Originally, these were developed for telesurgery, an application now rather on the back seat but still pursued by some groups [ , ]. Apart from legal issues and the difficult with consistency of the surgical team, telesurgery raises the problem of the transmission time between the master control and slave and the return to the surgeon. Time delay progressively affects surgical performance and task completion time, by introducing a latency in the visual control loop of the surgeon's brain. A significant decay is seen when this time lag is over 100 ms. When the latent time is over 300 ms, surgery becomes difficult, and at 700 ms, only very few surgeons are able to complete a surgical task [ , ]. Due to the high resolution image stream normally used to give the surgeon a realistic immersion in the operating field, hardware compression CoDecs are mandatory to minimize the latency times. Some telesurgery experiments on the RAVEN system in various situations (including undersea) have shown that the mean transmission delay was around 100 ms even when the distance between master and slave was as far as 6,000 miles [ ].

Telesurgery could be a solution to network a group of highly skilled surgeons to another set of difficult case patients, without surgeons needing to travel to another hospital. Highly trained surgeons could telementor local surgeons operating on patients in their own facilities.

Automated machines

These are machine tools dedicated to surgery, which operate by following a list of coordinates to access and possibly drill, in the same way as industrial machines. The only working example is the ProBot system developed at the Imperial College of London [ ]. A cutter is controlled by an algorithm running a list of coordinates of the prostatic tissue to be resected. An ultrasound probe linked to the robot provides direct control. The surgeon simply looks for the correct execution of the program via an urethroscope.

In ENT surgery, automated machines may be useful to perform rapid and accurate mastoidectomies or DRAF-3 frontal drill-out. However, this concept requires perfect patient immobilization (a Mayfield head clamp, for example), very accurate registration of the robot in the patient coordinate space and safety tests. Whereas any industrial machine-tool has to undergo extensive unitary testing prior to starting production, the same does not apply to surgery, where “production” is a single piece with no possible unitary test.

Collaborative robots

Also called cobots , collaborative robots have the ability to be directly and easily handled manually by the surgeon him/herself ( Figure 5.2 ). They can work both as automated machines for short sequences or by cooperating with any degree of compliance with the surgeon. This class of manipulators relies on its ability to be moved inversely from their distal part, a property known as backdriveability . Such systems are not simple to design as the actuators used by manipulators are usually mechanically geared in order to gain force/torque at the expense of motion speed (see previous chapter), giving the whole manipulator very low compliance. Special actuators and gearing trains are required to let these robots be moved effortlessly by the surgeon.

Until now, two types of collaborative manipulators have been described [ , ]:

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  parallel cobots which copy and follow the human movement and add to this their own force or accuracy. Some of these can have the same kinematic structure as a human body part (arm, leg or hand) and are usually called exoskeletons ¹

  1. An example of exosqueletton is the Hercule-V3® developed by the French company RB3D with the French Army. It helps a soldier to carry a higher payload and enable him/her to run faster (see www.rb3d.com ).

  ;

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  serial cobots form a serial kinematic chain where human and robot have complementary motions.

These systems are gaining increasing interest for industrial applications as they combine the different and complementary performances of human beings and robots. However, they have not stimulated significant interest for surgical applications and until now, their introduction in the field of surgery has been limited to the Surgicobot project [ ] and the SurgiMotion/SurgiDelta system (see chapter 10 ). Both are primarily parallel cobots.

We firmly believe that these deserve greater attention in the near future as they have the potential to combine the accuracy of electromechanical devices with the procedural skills of surgeons.

In vivo microrobots

These have been studied for heart surgery (HeartLander, dedicated to myocardial stem cell injection without sternotomy through a single 15 mm port [ ]) and to control the movement of a micro-endoscope in the gastro-intestinal tract [ ].