Two-photon polymerization (TPP) is a powerful and potential technology to fabricate true three-dimensional (3D) micro/nanostructures of various materials with subdiffraction-limit resolution. And it has been applied to microoptics, electronics, communications, biomedicine, microfluidic devices, MEMS and metamaterials. These applications, such as microoptics and photon crystals, put forward rigorous requirements on the processing accuracy of TPP, including the dimensional accuracy, shape accuracy and surface roughness and the processing accuracy influences their performance, even invalidate them. In order to fabricate precise 3D micro/nanostructures, the factors influencing the processing accuracy need to be considered comprehensively and systematically. In this paper, we review the basis of TPP micro/nanofabrication, including mechanism of TPP, experimental set-up for TPP and scaling laws of resolution of TPP. Then, we discuss the factors influencing the processing accuracy. Finally, we summarize the methods reported lately to improve the processing accuracy from improving the resolution and changing spatial arrangement of voxels.

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BackgroundRobot-assisted minimally invasive surgery (RMIS) is promising for improving surgical accuracy and dexterity. As the end effector of the robotic arm, the remote centre of motion mechanism is one of the requisite terms for guaranteeing patient safety. The existing remote centre of motion mechanisms are complex and large in volume, as well as high assembly requirement and unsatisfactory precise. This paper aimed to present a new remote centre of motion mechanism for solving these problems.MethodsA new mechanism based on the RMIS requirements is proposed for holding the laparoscope and generating a remote centre of motion for the laparoscope. The mechanism kinematics is then analysed from the perspective of the structural function, and its inverse kinematics is determined with a small number of calculations. Finally, the position deviation of the laparoscope rotational point is chosen as the index to evaluate the mechanism performance. The experiments are performed to test the deviation.ResultsThe position deviations of the laparoscope rotational point do not exceed 2 mm, which is lower than that of the existing remote centre of motion mechanism. The 2 mm positioning error of the laparoscope won’t affect surgeon observation of the surgical field, and the pressure caused by the positioning error was acceptable for the skin elasticity. The proposed mechanism meets the RMIS requirement.ConclusionsThe proposed mechanism can achieve the remote centre of motion for the laparoscope. Its simple and compact structure is beneficial to avoid the collision of robotic arms, and it can be applied on other robots for providing the instrument necessary motion in minimally invasive surgery.

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This article focuses on the nonlinear Wiener system identification of three-dimensional elliptical vibration cutting. The developed three-dimensional elliptical vibration cutting device is actuated by four piezoelectric stacks, which have hysteresis nonlinear characteristics. Our research proposes an improved memetic algorithm in order to identify the nonlinear elliptical vibration cutting model. The improved memetic algorithm displays the advantages of both particle swarm optimization and genetic algorithm, while simultaneously overcoming these programs' shortcomings. Moreover, it can quickly and efficiently search for the global optimization. The improved memetic algorithm's identification performance may be compared with the conventional memetic algorithm, particle swarm optimization, and genetic algorithm using two wellknown test functions. Test results demonstrate that the improved memetic algorithm can search the global optimal solution more efficiently than available state-of-the-art algorithms. Based on the input-output data collected from experiments, the accuracy of the identification model can potentially reach 97.55%. This relatively small margin of error verifies the efficiency of the proposed improved memetic algorithm for system identification.

In order to reduce the regression phenomenon of the piezoelectric stick-slip actuator, and improve the output performance, a piezoelectric stick-slip actuator with regular octagonal flexible hinge mechanism is proposed in this paper. The pseudo-rigid body method is used to analyze the regular octagonal flexible hinge mechanism and the flexible driving foot respectively.A prototype is fabricated to test the working performance and the results demonstrate that the minimum step is 0.01μm, the maximum speed is 145251μrad/s, and the maximum load carrying capacity is 500g. The experimental results show that the parasitic motion suppresses the regression of the actuator and improves the output stability.