Modular Instrument for the Minimally Invasive Surgery with SMA Actuation and Control

There is an increased use of minimally invasive surgery (MIS) in a wide range of medical operations. However, surgeons have to cope with the limitations of available instruments in terms of flexibility, handling and ergonomics. Manually actuated instruments like scissors or forceps often lack sufficient feedback because of friction. Robotic systems promise better handling, yet they are not affordable for the most clinical applications. Due to the requirement of high work capacity in minimal dimensions, shape memory alloys (SMA) imply potential to actuate instruments in MIS. Furthermore, SMA selfsensing characteristics demonstrate the ability to supply surgeons with position and haptic feedback. To apply these benefits we developed a multifunctional MIS instrument with SMA actuators and sensors. It is a modular system comprised of the operating unit, shaft, steering part and end-effector. The steering part allows a panning range of 90°. The effector is driven by tw antagonistically arranged PI-controlled SMA wires. The grasping force is estimated by nonlinear modelling within a deviation of 1N. Hence, this force can be used to apply a haptic feedback in the operating unit. Due to the electronic coupling of the components, it is possible to implement a programmable transmission function for the operator. Therefore, the sensitivity of the instrument is adjustable.