Development of a Tactile Feedback System for Robot Assisted Minimally Invasive Surgery (Ontwikkeling van een tactiel terugkoppelingssysteem voor robotgeassisteerde minimaal invasieve chirurgie)

Abstract

Minimally Invasive Surgery (MIS) continues to grow in importance and to gradually change and improve the medical practice. This technique comes with great advantages, such as lower risk, fast patient recovery and a reduced hospital stay, but requires an increased dexterity and concentration on the part of the surgeon. To solve those problems, robots were introduced that mimic the movements of the surgeons, allowing them to focus solely on the medical procedure. Currently, there is only visual feedback from the patient to the surgeon. The lack of haptic feedback is one of the most important drawbacks of minimally invasive surgery.To restore the tactile information channel, a tactile feedback systems has to be developed. Such a feedback system consists of two main parts. A tactile sensor to register the tactile information inside the patient, and a tactile display to reflect the tactile information to the skin of the surgeon. The requirements for such a tactile feedback system are derived from the properties of the human sense of touch in the application of soft tissue palpation.The first part of a tactile feedback system is the tactile sensor. After studying different sensor principles, elastoresistance is chosen for its simplicity and robustness, and examined more closely. Elastoresistance is found to be often poorly understood and its physical principle misconceived. Simple experiments show that only the contact resistance plays a role in an elastoresistive tactile sensor. The design of a new tactile sensor is discussed, together with improved readout electronics. These electronics are optimised for high speed and low interference with the sensor signal. They can easily be adapted for different sensitivity and resistance ranges, and only use very low voltages, which is relevant in the context of MIS. The prototype tactile sensor is simple, flexible, cheap, thin and adjusted for the desired pressure range, but still suffers from large hysteresis and drift.The second part of a tactile feedback system is the tactile display. After going through some general design guidelines, an overview is given on existing tactile displays with a slight focus on small scale shape displays. Several prototypes are built in an attempt to meet the challenging requirements. These include the first appearances of hydraulics applied in tactile displays. The first is a closed hydraulic system, profiting from the incompressibility of water to transfer the actuation over a distance. The second uses an open hydraulic system with a piezoelectric proportional valve to actuate the individual pins of the tactile display. A final prototype uses pneumatics and needs a pneumatic proportional valve to control the force of the pins. Existing commercial valves are too large to fit into an already crowded operating room, and make too much noise. Therefore a small and noiseless proportional valve is designed and built, which allows for easy integration into a compact array to operate the necessary large amount of pins. The pressure range which this valve can produce,however, is too small for a tactile display, and the design needs considerably more research before it can be employed.To realise an integrated, functional tactile feedback system a tactile display `lite' is built with commercial pneumatic valves. The aim of the system is to serve as a proof of concept rather than to fulfil all the requirements. It does stand out among other tactile displays found in literature. While there are displays with a larger bandwidth, a higher resolution or a higher force, none of them combines those in a single display. On top of that, the display is very compact and has an almost negligible weight. An experiment to evaluate the combined system shows that it allows to perform a relatively complex discrimination task, even though it is too difficult to distinguish a hard ball in soft tissue.nrpages: 149status: publishe