The micro/nano positioning field has made great progress towards enabling the advance of micro/nano technology. Micro/nano positioning stages actuated by piezoelectric actuators are the key devices in micro/nano manipulation. The control of piezoelectric actuators has emerged as a hot topic in recent years. Piezoelectric materials have inherent hysteresis and creep nonlinearity, which can reduce the accuracy of the manipulation, even causing the instability of the whole system. Remarkable efforts have been made to compensate for the nonlinearity of piezoelectric actuation through the mathematical modelling and control approaches. This paper provides a review of recent advances on the control of piezoelectric actuators. After a brief introduction of basic components of typical piezoelectric micro/nano positioning platforms, the working principle and modelling of piezoelectric actuators are outlined in this paper. This is followed with the major control method and recent progress is presented in detail. Finally, some open issues and future work on the control of piezoelectric actuators are extensively discussed.

Cell microinjection is a direct and effective way to transfer external materials into the cell. In the field of modern biomedicine, cell microinjection is very important, no matter in genetics, reproductive health, tumor therapy or others related research directions. Traditional manual cell microinjection has the disadvantages of low efficiency and low survival rate. In contrast, robotic cell microinjection can achieve precise and effective cell microinjection, and can be used in the injection of large quantities of cells. This paper reviews recent advances in robotic cell microinjection technologies. It summarizes the main approaches of key technologies and their advantages and disadvantages, such as cell identification, cell holding, precise positioning platform, cell injection strategy, sensors in cell microinjection, and cell modeling. The conclusion of the investigation is that the robotic cell microinjection has achieved remarkable results and still has great potential for further development. It is expected to be widely used in biomedicine and other fields to realize convenient, fast, and efficient microinjection operations of large number of individual cells. INDEX TERMS Robotic cell microinjection, cell identification, cell holding, precise displacement platform, injection strategy, sensors in cell microinjection, cell modeling.

Piezoelectric actuator is widely used in the field of micro/nanopositioning. However, piezoelectric hysteresis introduces nonlinearity to the system, which is the major obstacle to achieve a precise positioning. In this paper, the Preisach model is employed to describe the hysteresis characteristic of piezoelectric actuator and an inverse Preisach model is developed to construct a feedforward controller. Considering that the analytical expression of inverse Preisach model is difficult to derive and not suitable for practical application, a digital inverse model is established based on the input and output data of a piezoelectric actuator. Moreover, to mitigate the compensation error of the feedforward control, a feedback control scheme is implemented using different types of control algorithms in terms of PID control, fuzzy control, and fuzzy PID control. Extensive simulation studies are carried out using the three kinds of control systems. Comparative investigation reveals that the fuzzy PID control system with feedforward compensation is capable of providing quicker response and better control accuracy than the other two ones. It provides a promising way of precision control for piezoelectric actuator.

BACKGROUND: Spatial disorientation (SD) is a problem that pilots often encounter during a flight. One reason for this problem is that among the three types of SD, there is no validated method to detect the Type I (unrecognized) SD. OBJECTIVE: In this pursuit, initially we reviewed the problems and the evaluation methods of associated with SD. Subsequently, we discussed the advantages and disadvantages of the subjective questionnaire evaluation method and the behavior evaluation method. METHODS: On the basis of these analyses, we proposed a method to detect the unrecognized SD that improved the assessment of SD to a significant extent. We developed a new direction to study the unrecognized SD based on the subjective report and the center of pressure (CoP). RESULTS: The proposed evaluation method can assist the pilots to understand the feelings and physical changes, when exposed to unrecognized SD. CONCLUSION: We hope that this evaluation method can provide a strong support in developing a countermeasure against the unrecognized SD and fundamentally solve the severe flight accidents arising due to them.

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