Optimal force control of an IPMC actuated micromanipulator for safe cell handling

The demand for single cell manipulation to allow scientist to carry out medical researcher is fast increasing. To facilitate this advanced manipulation systems are required to permit both precise and safe handling of the biological cells. Current devices can achieve a high level of precision at the micro/nano scale but as a consequence are highly rigid and this stiffness puts the target cells at risk as there is no compliance or back-drivability. Ionic polymer-metal composites (IPMCs) are naturally compliant, giving them a 'soft touch', and now with recent advances in their fabrication and control IPMCs are showing major promise as safe and accurate cell manipulators. This paper presents the development of an optimally tuned force controller for a 2 degree-of-freedom (2DOF) IPMC actuated micro-manipulator. The control system has been implemented to demonstrate the ability to control the manipulator's applied force as a step towards implementing a truly safe system with active compliance control. The controller is adaptively tuned using a model-free iterative feedback tuning (IFT) approach which is ideal for operation in unknown cellular environments as well as for controlling the complex time-varying behavior of the IPMC actuators themselves. The IFT algorithm tunes the force controller by minimizing the design criteria, a least squares error, by 25% in the horizontal direction and 46% in the vertical direction. Experiments then show that the manipulator can accurately track a reference trajectory up to 4gf or ∼40mN in both DOF.