Ziqi Jin's research while affiliated with Soochow University (PRC) and other places

Piezoelectric actuators are characterized by high positioning accuracy, high stiffness and a fast response and are widely used in ultra-precision machining technologies such as fast tool servo technology and ultrasonic machining. The rapid response characteristics of piezoelectric actuators often determine the overall quality of machining. However, there has been little research on the fast response characteristics of piezoelectric actuators, and this knowledge gap will lead to low precision and poor quality of the final machining. The fast response characteristics of a piezoelectric actuator were studied in this work. Firstly, the piezoelectric actuator was divided into a no-load state and a load state according to the working state. A fast response analysis and output characteristic analysis were carried out, the corresponding dynamic model was established, and then the model was simulated. Finally, an experimental system was established to verify the dynamic model of the piezoelectric actuator’s fast response by conducting an experiment in which the piezoelectric actuator bounces a steel ball. The experimental results verify the correctness of the model and show that the greater the cross-sectional area and height of the piezoelectric actuator, the higher the bouncing height of the ball, and the better the dynamic performance of the piezoelectric actuator. It is believed that this study has guiding significance for the application of the dynamic characteristics of piezoelectric actuators in the machining field.

The piezoelectric actuator has been widely used in modern precision cutting technology due to its fast response speed and high positioning accuracy. In recent years, with the development of precision technology, modern cutting requires higher and higher cutting accuracy and efficiency. Therefore, this paper proposes a feedforward control method based on the modified Bouc–Wen (MBW) model. Firstly, a novel asymmetrical modified Bouc–Wen model with an innovative form of shape control function is developed to model the hysteresis nonlinearity property of piezoelectric actuators. Then, a self-adaptive cooperative particle swarm optimization (PSO) algorithm is developed to identify the parameters of MBW model. The comparative evaluation reveals that the MBW model outperforms the classical Bouc–Wen (CBW) model by 66.4% in modeling accuracy. Compared with traditional PSO algorithm, the self-adaptive cooperative PSO algorithm can obtain minimum fitness in parameter identification. Furthermore, the feedforward control strategy is realized to improve the position tracking accuracy. A position tracking experiment verifies that the feedforward control strategy improves the tracking accuracy of piezoelectric actuators significantly compared with the open-loop control strategy.

The small size and high flexibility of the mobile platform is widely used in many fields such as electron scanning microscope (SEM), but the mobile platform still adopts the structure of guide rail at present and has the problem of large volume and poor flexibility, which cannot meet the requirements of SEM for small cavity. Therefore, this paper proposes a small bipedal trans-scale precision positioning stage based on the inertial stick-slip driving to achieve small size and high flexibility. The mobile platform consists of two piezoelectric actuators, a frame structure, two bottom plates, two pre-tightening screws, and magnets, and the volume is 15 mm × 10 mm × 9.5 mm. To investigate the locomotion characteristics of the mobile platform, a prototype is manufactured, and a series of experiments are carried out. The experimental results show that its linear motion velocity can reach 3.553 mm/s and its angular velocity can reach 462.72mrad/s, which means that the mobile platform has good motion performance.

Stick–slip driving is widely applied because it provides a nearly infinite range of motion with sub-micron resolution, but its movement velocity is impacted by the dynamic response of high-voltage amplifiers. Therefore, this paper presents a high-voltage amplifier with a high dynamic response specific to stick–slip driving. Considering the capacitive load characteristic of stick–slip driving, an analog amplification circuit is designed to realize a high output voltage, and then a gate driving optimization method is proposed to improve the dynamic response performance of the amplifier. To verify the high dynamic characteristic of the voltage amplifier, an experimental system was built to test the dynamic response performance of the amplifier by monitoring the output voltage. The experimental results show that the gate driving optimization method improved the dynamic response performance by more than 10 times, and the amplifier can output an high dynamic voltage signal up to 150 V when driving a capacitive load of 0.5 μF.

In order to achieve the nano-operation in a limited space, a precision motion platform with a cubic centimeter volume based on the principle of inertial stick–slip driving is proposed in this paper. The mechanical structure and the operating principle are discussed. Kinematic models are used to analyze the performance of the prototype. To investigate the working performance of the prototype, a series of experiments are carried out. Experimental results show that the displacement outputs is related to the parameters of the electrical signal. The maximum moving speed of the platform reaches 13.1 mm/s when the driving frequency is 3.1 kHz. The maximum single step displacement reaches 4.8 μm. Through proper driving voltage and frequency, the proposed prototype can produce a satisfactory velocity.

This paper presents an improved autofocus method for human red blood cell images in a microscope. The products of the sum modulus difference and the real-valued fast Fourier transform function are multiplied to obtain an improved sharpness evaluation using the properties of a Gaussian function. It is superior to traditional evaluations in terms of unimodality, steepness, and sensitivity. A new quantitative criterion is proposed to represent the ability of sharpness evaluation against noise. An adaptive focus window with great robustness is proposed that can reduce the computation cost and adverse effects of the background. The better performances of the proposed algorithms are all proved by experiment results, and they can help to find the quasi-focus position more quickly and accurately.

The stick–slip driving is widely used in the field of nanotechnology because of its high resolution and theoretically unlimited displacement. However, it suffers from such problems as low velocity and one-step displacement instability. In this paper, a method to improve the performance of inertial stick–slip movement from the perspective of overturning moment is proposed. Firstly, modeling and mechanical analysis of the inertial stick–slip platform structure. Then analyzing the influence of overturning moment through the conservation of energy and getting calculation results. Finally, building an experimental system for verification and finding that the height of the inertial force dropped by 5 mm, and the prototype single step displacement increased by 26%. Through theoretical calculation and experiment, the influence of overturning moment on inertial stick–slip motion is verified, which provides further guidance for inertial stick–slip motion platform design.

In this paper, a large thrust trans-scale precision positioning stage based on the inertial stick–slip driving is proposed, which can output long range motion. The stage consists of a piezoelectric actuator, a cross roller guide, a pair of cantilever beams, the flexure hinge system and the gather system of grating ruler, and the volume is 30 mm (L) × 17 mm (W) × 17.5 mm (H). The structure and the driving principle are introduced in detail. To investigate the working performance, a prototype is fabricated and a series of experiments is carried out. Experimental results demonstrate that the displacement outputs under various driving voltages, various driving frequencies and various step response time show good linear relationships with the time. The maximum thrust and the maximum load capacity are 6.1 N and 2500 g. The displacement and the driving resolution can reach 20 mm and 5 nm. The velocity can reach 12 mm/s when the driving frequency is 2.5 kHz. The experimental results also confirm that the designed stage can achieve various speeds by changing the driving voltage and driving frequency.

Predicting the focal plane is an effective method to increase the scanning speed of an automatic microscopy system. However, the image easily defocuses when using traditional predictive scanning methods. In this paper, we introduce an adaptive predictive scanning method (APSM) that greatly improves the accuracy of predictive scanning. Instead of using a fixed planar model to predict the focal plane position, APSM updates the predicted focal plane in real time based on the focal position of the reference point during the scanning process, thus predicting the focal position of each local view more accurately. Using the APSM, the average image defocus value is 0.39 μm, while conventional predictive scanning methods reach 1.05 μm. APSM greatly improves focal accuracy and can be applied to a high-precision automatic microscopy system.

The piezoelectric-actuated inertial stick-slip device (PAISSD) has been applied extensively. However, it is difficult for the PAISSD to achieve nanometer positioning under large stroke. In addition, the speed of the PAISSD is unstable because of the inconsistent surface roughness and different abrasion. Toward solving these problems, this paper presents a method of double closed-loop control with the speed and the position. First, the position closed-loop method is introduced in detail to achieve rough positioning in the stepping mode. Second, the driving waveform is designed to make the speed and frequency of the PAISSD present a linear relationship and the speed closed-loop performance is theoretically analyzed. Finally, the validity of speed and position double closed-loop is verified via experiments. The positioning accuracy of the PAISSD is 50 nm, and the repeated positioning accuracy is 80 nm. The error of average speed is less than 1.1% and the standard deviation is less than 0.1 mm/s.