Actuator Array for Use in Minimally Invasive Surgery

For tactile-haptical feedback in minimally invasive surgery, a tactile actuator array consisting of 8 x 8 actuators is being built. The system is combined with a tactile optical sensor system mounted in a laparoscopic forceps, providing 8 x 8 signals. These signals have to be shown as a true-scale representation through the actuator array. Therefore each measured pressure signal is coded into a corresponding actuating displacement. Each actuator is made out of a SMA-spring conditioned with the one way effect. The SMA spring works against a bias spring and both are mounted on an electrically isolated base pin. The bias spring produces a linear rising force against the SMA-spring for resetting the actuator during the passive cooling time. The whole actuator has a diameter of 1.6 mm, a length of 25 mm and is mounted at a distance of 3.2 mm from the next actuator. The resulting force of a single actuator while pressing against the surgeon's fingertip is over 2.5 N, and the actuating displacement is about 3.5 mm. Each pin has analogue adjustment and can be stopped at all positions within these 3.5 mm deflection. The resetting time is about 10 seconds and is reached with 3 fans mounted on three sides of the actuator array. The aim is to build a minimally invasive palpation system so that the surgeon can 'feel' with his laparoscopic forceps.