Onboard visual micro-servoing on robotic surgery tools

Precision motion actuation is a key technology for miniature medical robotics in a variety of applications, such as optical fibre-based diagnosis and intervention tools. Conventional inductive actuation mechanisms are challenging to scale down. Piezoelectric materials offer a scalable, precise, fast and high-force method but at a limited displacement range. In previous work, the combination of piezoelectric beams (benders) with compliant motion translation structures has been shown to be promising for robotic micro-actuation. In this paper, this approach is employed to implement a three degrees of freedom delta robot, suitable for catheter, diagnostic optical fibre and microsurgery tool manipulation. The fabrication process combines additive manufacturing, origami structuring and piezoelectric beam assembly. Closed-loop control is implemented using a new, on-board visual feedback concept. In contrast to typical optical motion systems, the fully internal visual feedback offers system compactness with precise and reliable camera-to-marker geometry definition. By employment of this method, a delta robot with motion accuracy of 7.5 μm, resolution of 10 μm and 8.1 μm precision is demonstrated. The robot is shown to follow a range of programmable trajectories under these specifications, and to compensate for externally applied forces typically expected during microsurgery manipulations. This is the first, to our knowledge, demonstration of micromotion control using internal visual feedback, and it opens up the way for high-resolution compact microrobots.