Optimization of a piezoelectric bimorph grasper for use in minimally invasive surgical applications

The potential use of piezoelectric bimorph actuators in minimally invasive surgery suture-needle grasper/holder applications is explored computationally. Upon defining the design/functional requirements for such surgical tools, a finite element analysis of the underlying piezoelectric boundary value problem is combined with the genetic algorithm optimization routine to arrive at an optimal morphology of the suture-needle grasper/holder. The results obtained show that, if the actuator is based on several constant-thickness segments, a proper combination of thicknesses of such segments can substantially improve the performance of such surgical tools. Specifically, a good combination of the relatively large grasper-jaws opening and the required level of the holding force when the grasper is closed on a 0.5 mm diameter suture-needle is obtained. The effect of orientation of the poling direction in the piezoelectric layers on the performance of the bimorph actuator is also examined. It is found that, at the same level of the required grasping force, a change in the poling direction by about 2.3° from the through-the-thickness direction can increase the maximum grasper-jaws opening by about 10 per cent.