Development and analysis of a tip-separated flexure needle based on piezo actuation

The bevel-tip flexure needle will naturally bend during insertion in soft tissue due to the tip asymmetry. Therefore the needle enables robotically steering by rotating the needle tip resulting from the needle base rotating. However a significant orientation discrepancy between the needle tip and the needle base caused by the friction torque between the needle shaft and the tissue results in inaccurately steering. To address this problem, a tip-separated flexure needle actuated by the shear piezoelectric actuator (SPA) based on the stick-slip theory is proposed in this paper. Compared to the conventional needles, the proposed one is directly driven at the tip end, which will significantly decrease the friction torque in the inserting procedure. Essentially, the separated tip is a rotary motor based on the piezo actuated. To verify the feasibility of the proposed design for the insertion application, the motion performances of the rotary motor such as the load capacity, step characters are analyzed by the established model in this paper. Furthermore, an experimental setup with an enlarged rotary motor is designed and fabricated. Finally, it is verified that the motion performance has no connection to the motor size, i.e., the tip can, in some extent, be downsized according to the actual requirement. The proposed piezo-actuated tip can also been employed in other micro scale application as a rotary actuator.