Design, Fabrication and Realization of a Parallel Microrobot at the Millimeter Scale for Minimally Invasive Surgery

The parallel mechanism actuatedbypiezoelectricactuators possesses remarkable advantages of high precision, large stiffness,and excellent dynamic characteristics, and can be integrated to miniature size, thus has great potentials in the application of minimally invasive surgery. A piezo-actuated parallel microrobot at the millimeter scale for minimally invasive surgery is developed. The proposed microrobot is driven by two piezoelectric bimorphs independently. Inspired by the flapping wing mechanism of the dragonfly, a bionic four-bar amplification mechanism which converts the micro driving displacement of the piezo actuators into a large rotation of the base link is designed. And a parallelogram linkage mechanism is introduced to enhance the stiffness and stability of the microrobot. The velocity Jacobian matrix of the developed microrobot is established. The optimal dimensions of the robot links are determined by evaluating the dexterity and global conditioning indexes. Then, a laser micromachining and lamination processes based on the smart composite microstructure is proposed for the integrated fabrication of the microrobot prototype. By doing this, the complex three-dimensional structure of the proposed microrobot with multiple links is obtained through a series of fabrication processes including laser cutting, laminating, folding, releasing, and assembling of multiple laminate layers. The fabricated microrobot has dimensions of 21 mm×26 mm×5.6 mm, and a mass of 3.05 g（including actuators）. Finally, open-loop experiments are conducted on the tracking performances of the developed microrobot when repeatablely following horizontal line, vertical line, circle,and sinusoidal trajectories. Under an excitation amplitude of 55 V, experimental results show that the motion stroke, relative error,RMSE, and repeatability RMSE of the proposed microrobot are 2.12 mm, 0.93%, 19.7 μm±0.5 μm, 8.5 μm±0.4 μm for the horizontal line, and 2.01 mm,0.52%, 10.5 μm±0.4 μm, 4.9 μm±0.2 μm for the vertical line, respectively. Therefore, the developed microrobot demonstrates the high positioning accuracy and effective tracking capabilities.