【作者】 张杰；

【导师】 冯志华；

【作者基本信息】 中国科学技术大学 ， 测试计量技术与仪器， 2015， 博士

【摘要】 在微致动与精密定位领域,压电致动器由于位移分辨率高、输出力大、动态响应好等优点得到了广泛的应用。然而由于压电材料自身的迟滞与非线性等特性,基于压电致动器的微定位系统的性能往往受到很大限制,为此,研究人员提出了很多的办法,其中最常用的三种方法为：前馈控制方法、反馈控制方法、电荷控制方法。本论文在前人研究的基础上对用于压电致动器的两种新型驱动方法：开关电容电荷泵方法与结合应变反馈和电荷放大的混合驱动方法,进行了详细的理论分析与实验验证,并实现了两种方法在原子力显微镜中的应用。本论文对一种新颖的开关电容电荷泵方法进行了详细的分析,并将之成功地应用于原子力显微镜中扫描成像。本文对开关电容电荷泵的工作原理进行了详细分析,分别对充电电容、模拟开关、运算放大器对电荷泵电路的影响进行了分析。对开关电荷泵产生的阶跃位移进行了频谱分析,指出应该尽量实现“小步快跑”的扫描方式。对开关速度对电路的影响进行了分析与探讨,并针对性地提出了一种高速放电的开关电容电荷泵电路。然后搭建实验装置,以普通蓝光光盘为样品,使用开关电容电荷泵方法在原子力显微镜中实现了传统的光栅式扫描(Raster Scanning),成像结果亦表明相对于电压驱动扫描,开关电容电荷泵方法能有效地减小迟滞与非线性,图像质量有很大提高。针对开关电容电荷泵方法的低频漏电问题,提出了一种基于开关电容电荷泵的螺旋线扫描方法。对此方法下压电致动器上的电荷量进行了推导,分析比较了同等扫描情况下光栅式扫描与螺旋线式扫描的速度对比,发现螺旋线式扫描的速度是光栅式扫描的(?)倍。针对螺旋线扫描这种特殊的扫描方式,开发了一个对应的图像算法。本论文首次提出了一种结合应变反馈控制和电荷放大的混合驱动方法,用以解决包括开关电容电荷泵在内的电荷驱动方法的低频漏电问题。基于传感器的反馈控制是最成熟最流行的一种方法,它主要使用位移传感器来探测压电致动器的输出位移,并形成闭环控制系统。由于传感器噪声的存在,高分辨率与高带宽成为不可兼得的两个量,因而反馈控制方法通常都是应用在低频频域。电荷控制方法的理论基础为压电致动器的输出位移与其上的电荷量(而不是施加的电压)成线性关系。电荷放大器在高频频域有着良好的线性度、高分辨率、以及快速的动态响应,但是在低频频域由于漏电以及一些非理想因素的影响,其往往退化为电压放大器,因而电荷放大器主要是用在高频频域。本文提出一种混合控制电路,它使得应变反馈回路主要工作在低频频域,而使电荷放大回路主要工作在高频频域,这种方法结合了反馈控制方法与电荷控制方法的优点,而弥补了各自的缺点。通过对混合控制电路及其传递函数的分析,从理论上证明了应变反馈控制与电荷控制的频率响应能实现无缝对接。对应变反馈回路以及电荷放大回路的噪声水平分别进行了详细分析,数据表明单独使用应变反馈控制时,对于10kHz带宽所能达到的最高位移分辨率为4.4nm；而单独使用电荷放大器时,对于10kHz带宽所能达到的最高位移分辨率为48.8pm。以三维尺寸为10mm×10mm×20mm的压电堆栈致动器为实验对象,对以上混合驱动方法进行了性能测试,当给压电堆栈施加一个三角波激励时,在0.1Hz～50Hz的频率范围内混合驱动方法均有稳定的增益,而且输出位移的非线性度均小于2%。将应变反馈回路与电荷放大回路的带宽均设为1kHz时,应变放大器输出的位移噪声理论计算值为1.9nm,实际测量值等效为2.5nm；电荷放大器输出的位移噪声理论计算值为25pm,而实际测量值等效为30pm。通过混合驱动与单独使用应变反馈的对比,也证明了混合驱动具有良好的动态响应。提出了一种改进型的混合驱动方法,并将之成功应用在原子力显微镜中进行扫描成像。将以上混合驱动方法用来驱动原子力显微镜中的压电扫描器时,一个绕不开的问题就是压电致动器是虚地连接的,这在实际扫描当中会导致系统易受干扰。为此,设计了一个基于“镜像驱动”的改进型混合驱动方法,它同时使用一个参考致动器和一个目标致动器,通过使用混合驱动方法控制虚地连接的参考致动器,从而间接地在实地连接的目标致动器上实现高线性度和动态响应。对传递函数的分析也证明了此方法的可行性。此方法被成功地应用于商用原子力显微镜(NanoFirst3000)中,扫描图像也表明,在使用此改进型的混合驱动方法时压电致动器的迟滞和非线性被大大减小,扫描图像的质量得到了很大提高。更多还原

【Abstract】 In the micro actuating and precise positioning area, piezoelectric actuators (PZAs) have been widely used because of their advantages of high displacement resolution, large output force, and excellent dynamic response. However, the performances of the precise positioning system based on PZAs are largely limited because of the inherent properties of the piezoelectric material, such as the hysteresis and nonlinearity exhibited between the output displacement and applied voltage. Researchers have proposed many methods to overcome these problems. The most adopted methods are: feedforward control, feedback contro1and charge control. In this dissertation, two novel charge control methods for the PZAs, the switched capacitor charge pump (SCCP) method and a hybrid control method, are investigated theoretically and experimentally. Both methods are successfully implemented in a atomic force microscope (AFM) system.The novel switched capacitor charge pump method was carefully analyzed and successfully applied in an AFM for scanning. The working principle of the SCCP method is explained in detail. The influences of the chaging capacitor, the analog switch, and the operational amplifier to the circuit are analyzed. The influence of the switching frequency is also analyzed. In order to increase the switching frequency, an improved SCCP circuit with fast discharging is proposed. We build the experimental setup and employ an ordinary bluray disk as the scanning sample. The SCCP method is successfully implemented in an AFM to realize the traditional raster scanning. Imaging results demonstrate that the hysteresis and nonlinearity are reduced evidently under the SCCP drive, compared to the linear voltage drive. Facing with the low-frequency leakage problem of the SCCP method, a SCCP-based spiral scanning is proposed. The charge on the actuator is caculated carefully under the SCCP-based spiral scanning. Results show that the charge signal is a sine signal with linearly-varying amplitude, and the method is achievable. The scanning speeds of the traditional raster scanning and the spiral scanning are analyzed and compared. Results show that the scanning speed of the spiral scanning is1/2π times higher than that of the traditional raster scanning. At last, an image construction algorithm is developed.A hybrid control mehtod combining strain feedback control and charge control is firstly proposed in this dissertation. The hybrid control method is supposed to solve the low-frequency leakage of the charge control methods, including the SCCP method. The sensor-based feedback control is the most popular control strategy for the PZAs. It mainly uses a displacement sensor to detect the movements of the PZAs, and forms a closed-loop control. Because of the sensor-induced noise, high resolution and wide bandwidth can not be achieved simultaneously. Therefore the feedback control is mianly applied in the low frequency domain. The fundamental theory about charge control is that the output displacememnt of the PZAs is proportinal to the charges, but not the applied voltage, on the actuators. The charge amplifiers exhibit good linearity, high resolution, and fast response in the high frequency range. However, they usually become a voltage amplifier in the low frequency range due to the low-frequency leakage. Therefore the charge control method is normally used in the high frequency range. The proposed hybrid control method combines the advantages and avoids the disadvantages of the feedback control and charge control, by making the strain feedback control loop functioning in the low frequency range and the charge amplifying loop functioning in the high frequency range.The transfer function of the hybrid control method is analyzed in detail. It is theoretically proven that the frequency response of the strain feedback control and the charge control can cooperate with each other. The noise levels of the strain feedback loop and the charge amplifying loop are analyzed carefully. Results show that the achievable resolution is4.4nm for a bandwidth of10kHz under the strain feedback control alone; the achievable resolution is48.8pm for a bandwidth of10kHz under the charge control alone. Employing a piezoelectric stack which has a dimension of10mm x10mm x20mm as the experiment target, the hybrid control method is tested. Giving the piezoelectric stack a triangular excitation, the hybrid control method has stable gain in the whole frequency range from0.1Hz to50Hz, and the nonlinearity of the output displacements is less than2%. When the bandwidthes of the strain feedback loop and the charge amplifying loop are both set at1kHz, the theoretical output displacement noise of the strain amplifier is1.9nm while the measured equivalent displacment noise is2.5nm; the theoretical output displacement noise of the charge amplifier is25pm while the measured equivalent displacement noise is30pm. By the comparison of the hybrid control and feedback control, the hybrid control is proven having fast response.An improved hybrid control method is proposed and successfully implemented in an AFM for scanning. When the original hybrid method is applied to drive the piezoelectric positioner in the AFM, an existing problem is that the piezoelectric actuator is float-grounded, which may cause disturbation to the system. An improved hybrid control method based on "mirror control" is proposed to overcome this problem. A reference actuator and a target actuator are employed. The grounded target actuator is indirectly controlled by linearizing the charges on the float-grounded reference actuator. The linearized charges on the reference actuator results in linear displacement of the target actuator. The analysis of the transfer function proves the feasibility of the method. The improved hybrid method is also successfully implemented in a commercial AFM for scanning. Imaging results show that the hysteresis and nonlinearity are largely reduced by using this improved hybrid method, and the image quality is improved evidently.更多还原