Research On A Hexapod Piezoelectric Robot For Cross-scale Micro/nano Manipulations

Micro/nano manipulation robots play important roles for humans in the process of exploring and reshaping the microworld.Among so many micro/nano manipulation robots,the type using piezoelectric driving mechanism has the best comprehensive performances and the most extensive applications,so it has received extensive attention and research.Although there are a variety of actuation principles for the existing piezoelectric robots,they generally specialize in only a certain motion performance.It means that none of them accomplish the integration of high motion accuracy,large workspace,strong load capacity,fast response velocity and multiple degrees of freedom on a single piezoelectric robot.This problem has not been effectively solved by now,so it greatly limits the research and applications of piezoelectric robots in many high-performance micro/nano manipulations,and restricts the developments of them.In order to address the above issue,a bioinspired piezoelectric multilegged stepping actuation principle is proposed,which takes the multi-DOF motion of a single leg as the foundation,takes the collaborative operation of multiple legs as the key,and takes the fusion of multimode motions as the kernel.It can be summarized as a design philosophy for piezoelectric robots with the ability of multi-DOF cross-scale motions,so as to guide the design and motion planning of these robots.The proposed principle is illustrated and verified with theoretical analyses and experimental studies,which contributes to integrating the multiple performance requirements on a single piezoelectric robot.Following the proposed design philosophy,a series of feasible configurations of piezoelectric robots are proposed,and the hexapod piezoelectric robot is selected as the main research object due to its broad application prospects.The detailed physical design is conducted based on the constructions and the motion laws of piezoelectric driving elements.The wobbling gait,the slipping gait and the walking gait are planned and fused on the single structure of the robot,the actuation principles of these gaits are deeply elaborated,and the efficient excitation methods are designed for them.Hence,the robot can be driven and controlled with the multiple motion gaits.According to the structural features and actuation principles of the hexapod piezoelectric robot,the motion system of the robot is decomposed into several segments.Each of segments is abstracted from a mechanical model into a physical model,and the mathematical model is derived from the physical model.Finally,the whole dynamic model of the robot is established by integrating all the mathematical models.The output displacement of the robot at any input voltage can be calculated with this dynamic model,so the numerical simulations are conducted to study the motion laws of the robot with the three gaits.They indicate that the wobbling gait is suitable for the high precision motion in a small range.The slipping gait is convenient to reach an unlimited stroke,but its load capacity is weak.Meanwhile,the walking gait accomplishes an unlimited stroke and a great motion robustness versus varying loads,but its excitation method is relatively complex.The effective mechanical output intervals of the three gaits are complementary,so a collaborative driving strategy for multiple switching gaits is developed to accomplish the integration of the multiple performance requirements on a single robot.The simulations of the three basic gaits not only shows their motion performances,but also reflects the deficiency that the fusion of these gait is only suitable for the point-topoint control with low speed.Hence,three improved gaits are proposed to further improve the motion performance and expand the application of the robot.The improved slipping gait completely eliminates the inertial rollback,and converts the stepping motion into the continuous motion,so the application field of the robot is extended from the precise point-to-point control in a large range to the precise trajectory tracking in a large range.The improved walking gait completely eliminates the speed fluctuation and the varying inertia force,which makes the robot can move smoothly at an ultra-low speed,so the motion ability is extended from the cross-scale displacement control to the cross-scale displacement and cross-scale velocity simultaneous control.The jumping gait breaks the restriction that the step stroke of the robot cannot exceed the workspace of a driving leg,and generates the larger step distance and faster velocity,so the robot gets suitable for the applications requiring fast and accurate motions.Many experiments and applications are conducted on the basis of the above theoretical analyses.After developing the prototype of the robot,the driving system,the control system and the motion sensing system are designed to construct the experimental testing platform,so the motion law of the robot can be evaluated with the experimental data.The experimental results indicate that the single driving leg can generate high dynamic3-DOF precise trajectory synthesis motion in a range of 15.2 μm × 14.7 μm × 17.3 μm,which meets the actuation requirement of the robot.With the cooperation of the three basic gaits,the robot obtains the positioning accuracy higher than 5 nm in a range of0.2 mm × 0.2 mm,the speed of 1.89 mm/s and the load capacity larger than 22 times of its own weight,which means the integration of the multiple performance requirements.Driven by the three improved gaits,the trajectory tracking accuracy of the robot is higher than 0.12 μm in a range of 0.4 mm,the smooth velocity control can be realized from3.97 nm/s to 1.16 mm/s,and the fastest speed increases to 4.0 mm/s.It means that the motion performances of the robot are further improved with the improved gaits.Some applications of the robot are also tested,which include the transfer and assembly of micronano particles,the probe detection of wafer,the microstructure ruling process on a large surface and the batch injection of multiple cells.They prove the practical significances brought by the improvement of the robot motion performance,and expand the applications of piezoelectric robots.The theoretical analyses and experimental verifications in this dissertation all take the hexapod piezoelectric robot as the research example,but it should be noted that the proposed design philosophy and the research method are universal.They can provide theoretical reference and technical support for the design and motion planning of other types of micro/nano manipulation robots,so as to promote the consistent progress of relevant research and expand their applications in high-performance micro/nano manipulations.