Overview of current and past research topics of RAS
Soft tissue overload prevention
A drawback of current surgical master-slave systems is the fact that the surgeon cannot feel what happens at the slave side. By implementing adaptive threshold levels into the control strategy of the master-slave system, it is possible to limit tissue damage. In current robot-assisted surgery procedures there is, for instance, a risk of tearing an artery because of excessive pulling forces. This new method deals with this type of risks. Presently, research is conducted on experimentally setting the threshold levels for damage, through in vitro and in vivo experimentation and functional and histological examination, and with the help of finite element modelling, integrating the concept into the master-slave system.
Bilateral Teleoperation: linear controllers
Bilateral teleoperation provides force feedback and allows the surgeon to feel what he/she is doing. To analyze the fundamental performance limits of bilateral teleoperation, the bounded environment passivity method has been proposed. This method to study stability allows to include or derive bounds on the environment properties. Using this method, a set of rules of thumb for both hardware and control design have been defined.
Based on these rules of thumb the LoTESS system has been developed. This teleoperation system provides reliable force feedback and has telesurgery as the intended application.
Force measurement systems
An important problem in robotic surgery is that the surgeon lacks tactile feedback (feeling). This can be solved by introducing force sensors in the instruments that enable force reflection in the 'joysticks'. In the past, force sensors have been integrated in the instrument shaft outside the patient's body as the sensor size is less restricted outside the body. However, the contact forces with the trocar (point where the instrument enters the body) and inertial forces on the instrument shaft disturb the measurement. The best solution, but technically the most challenging, is to integrate a miniaturised force sensor at the instrument tip.
Therefore, we developed a 5 mm diameter tri-axial force sensor that can be integrated in the instrument tip. The required force range and resolution have been determined by in vivo-tests. The sensor is based on a flexible titanium structure of which the deformations are measured through reflective measurement with 3 optical fibres. It has a range of 2,5 N in axial direction and 1,7 N in radial direction, and a resolution of 0,04 N.
Tactile Feedback
A force feedback system returns a single value of the experienced force. A surgeon, however, often uses palpation, and with that his sense of touch, to make decisions in open operation. He feels the pressure distribution on the surface of his finger and can observe a number of features in the tissue. When the endoscope is obstructed it can also be useful to guide the instruments by hand. The aim of this research is to make tactile feedback available during minimally invasive surgery.
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Eye Surgery
When anatomical structures become really small and fragile, chances for failure during medical interventions rise sharply. Some treatments on the retina at the back of the eye require that much precision that they are only attempted when all other options fail. Surgical robotics can come at an aid here. Supported by a Marie Curie IRG grant, STREAM, the RAS group is already a couple of years active in robotic eye-surgery. Some promising results are described in these publications.
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Robotic laser surgery
The aim of this research is to apply a laparoscopic robot to improve and facilitate the procedures of laser laparoscopy performed by gynaecological surgeons. The main idea is to take advantage of the existing endoscopic robot. With a digitiser tablet and wireless pen, we create an intuitive interface for this particular purpose.
The What-You-See-is-What-You-Cut (WYSIWYC) control scheme provides surgeons with a natural interface to perform laser ablation as if he is sketching by pen. The auto-focus functionality helps surgeons by focussing the laser automatically with an endoscopic distance sensor. Some safety measures are installed in the DSP controller. The accuracy of the robot is examined with a sinusoidal test and is more than demanded in laser laparoscopy.
Steerable instruments
To further increase the manoeuvrability and the working volume, more degrees of freedom need to be actuated inside the human body. A system with more than six degrees of freedom will give the surgeon the possibility to operate behind organs and at positions that can not be reached with current minimally invasive instruments. Such a system will also be able to improve the camera positioning and as a consequence the patients safety. High force density micro actuators are necessary in such a system. Current research focusses on the development of the actuators and the integration of actuators, sensors and control electronics in a compact intra-corporal robot.
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