The Design and Characteristic Study of a 3-dimensional Piezoelectric Nano-positioner

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1 SICE Annual Conference August 8-,, The Grand Hotel, Taipei, Taiwan The Design and Characteristic Study of a -dimensional Piezoelectric Nano-positioner Yu-Chi Wang Department of Mechanical Engineering National Chiao Tung University Taiwan ronald745@gmail.com Li-Kang Chen and Shao-Kang Hung, Member, IEEE Department of Mechanical Engineering National Chiao Tung University Taiwan skhung@mail.nctu.edu.tw Abstract This paper presents a mechanical design method of thin column group guidance and multi-actuator parallel mechanism for three degrees of freedom translations, since multiactuator parallel mechanism is utilized to implement planar motions which are general requirements for the nano-positioner. The traveling range of this nano-positioner is 5 μm in the X-, Y- directions and in the vertical direction. The three-dimensional nano-positioner has several advantages such as low-cost, highprecision, and can be applied to the assembly, processing, biotech and medicine detection and semi-conduct industry. In the feedback controller, we choose MATLAB/Simulink, Real-Time Workshop, a software widely used by the academic community, as tools to study rapid controller prototyping. The parameters are controlled based on proportion-integral control law that is easily used and has a good performance. Keywords: nano-positioner, Piezoelectric, Simulink, AFM, PID, thin column group I. INTRODUCTION The needs for precise nano-positionr raise in many fields of research and technology, such as in cellular biology, scanning tunneling microscopy (STM), atomic force microscope (AFM) []. High-speed AFM is required to observe these processes in real-time. The requirement of positioning system with submicron order accuracy increases with the developing of precision engineering. Secondly, the piezoelectric material is more important in submicron positioning systems for its merits in electromechanical couple. The features of piezoelectric material, such as less weigh, small size, fast response, high resolution, etc., have made it valuable for application in position engineering [-4]. However, regarding to the displacement precession of piezoelectric devices are limited by the hysteresis phenomenon, furthermore the maximum deformation for a piece of piezoelectric material is quite small for most application. In order to improve these properties, the new compositions of the piezoelectric material and multiplayer piezoelectric ceramics have been developed these years. The reformed piezoelectric devices with these reformed piezoelectric elements may obtain greater displacement and higher precision. Piezoelectric elements-driven ultra-precision stages [5] have been utilized for their high accuracy, fast response, and high load capacity. In reviewing literatures, Merkle [6] discusses a new family of six degrees of freedom positional control devices which generally combine simple designs, high stiffness and strength, and a wider range of motion. Chang and Du [7] integrated traditional Scott-Russell straight-line mechanisms with a flexible structure arrangement. In their design, a piezoelectric actuator was used to drive two sets of Scott-Russell straight-line mechanisms in order to amplify the output displacement of the piezoelectric actuator and to ensure a straight-line displacement of the positioning device output. By linking a parallel guide spring to the output end of the positioning device, a piezoelectric-driven positioning stage was developed with a displacement range of m, a displacement resolution of 4 nm and an angular deviation of. rad. Hansma [8] specifically design the piezoelectric scanner for the high-speed atomic force microscope, and its speed compare to the general commercialization of nano-positioner is much faster. In 7, Hansma [9] design a new type of piezoelectric scanner for the high-speed atomic force microscope. They demonstrate the performance of the high-speed AFM [] system a silicon calibration grating and a biological specimen are imaged at a scan-rate of 6 lines/s and a resolution of pixels. II. SYSTEM DESIGN The experimental setup, shown in Fig, has been designed such that the stage can be actuated using free weights. The nano-positioner can be divided into three parts. One is the moving stage, another part is the piezoelectric actuator, the other is the column group. In order to achieve X-, Y-, and Z- direction are parallel separately, so we use a "thin column group" which one of the directions is high-rigidity and two are low-rigidity. Because the "thin column group" is a high-rigidity axial, and the PR//79 4 SICE

2 displacement of platform can be generated by the piezoelectric actuator. But "thin column group" in the other perpendicular directions are low-rigidity, it produces a similar deflection of the role of guidance, which the principle and the "parallel flexures" on the same principle []. "thin column group" has many advantages, but not easy to manufacture. First, because it needs to complete the two directions of wire cutting electric discharge machining, it must produced the "parallel flexures" and next, the "parallel flexures" rotate 9 degrees, and use wire electrical discharge machining cutting production make it a "thin column group". reduce external disturbances on sensing and measurement system, a Shinhan optical table is used to support the - dimensional nano-positioner. The selected piezoelectric actuator can generate a displacement of up to μm, has an axial stiffness of 6 N/μm and can deliver a maximum driving force of N. A digital computer is used to implement numerical control, user interface and supervisory control operations. Thin Column Group PZT Actuator Fig. Experiment setup for system identification. Fig. Photograph of the fast -dimension nano-positioner showing the twelve piezoelectric actuators integrated in the exure system. In order to achieve high precision positioning, a proper feedback controller is necessary for precision positioner. Moreover, the entire system also suffers from external disturbance from the environment and such as magnetization drifting and air-gap coupling that need to be effectively suppressed for precision motion control. Therefore, the desired controller should be robust enough to deal with theses uncertainties and disturbances. In the industry, the Proportion-Integral-Derivative (PID) controller is a very popular control method. Due to its simple structure, this kind of controller can be easily implemented in many systems. To eliminate the nonlinearity of piezoelectric actuator, PI closed-loop control should be utilized to eliminate the hysteresis and creep, as well as the motion errors in flexurebased guideway. Based on the established displacement mapping and control models, it is feasible for the real-time calculation from the sensor signals of the position and orientation errors and compensation control voltages to be supplied to the twelve piezoelectric actuators to adjust the pose of the moving platform. Thus, the motion and positioning accuracy can be improved. The experimental procedure is shown in Fig. In order to We use the laser displacement sensor to measure the horizontal displacement of the nano-positioner and get the feedback signal to personal computer, and then the magnitude and phase of every frequency would be plotted in real time. They are manufactured by keyence, with 9 khz sampling frequency, m active range, and. m accuracy. So far, we have achieved satisfactory performance using this kind of sensors. The piezoelectric amplifier module has a nominal amplification factor of.75±., and can output and sink a peak current of A. The software environment is the Matlab Real-Time Windows Target of Version., which is a PC-based solution for real-time application. After constructing a model and simulating it with Simulink in normal mode, we can generate executable code with Real-Time Workshop and the C/C++ compiler. Then, we can run the real-time application with Simulink in external mode. III. EXPERIMENTAL RESULTS We show a number of experimental results including regulation, step-train, sine wave motion, triangle wave motion, cycling motion, and spiral motion will be provided in this part to demonstrate the performance of this system. A. Regulation Response In regulation response, we only consider the response performance in Z-axis and we set the initial points as: X = - 8 -

3 μm, Y = μm, Z = -μm. In the experiment, we appropriately adjust the PID parameters so that the configuration states can converge to the point at X = Y =, and Z = μm. Fig. show the success of the proposed PI controller in the regulation test. B. Step-Train Response Here we made a continuing stepping response experiment with each step equal to.5μm. The experimental results of stepping are shown in Fig 4. fundamental frequencies of Hz, Hz, Hz, and 5Hz along X-axis and Y-axis. When the frequency exceeds Hz, the peak of the triangular wave becomes relatively smooth. Hz - X-axis Sine Wave Test Hz X -axis Regulation Response Test Fig. Z-axis ramping experimental, Z state, and the steady state error of Fig can converge to 45nm. C. Sine Wave Motion In order to test the tracking and contouring capability of this proposed -dimensional nano-positioner system, we present the experimental results of the sine wave motion with the amplitude equal m at every frequency along X-axis and Y-axis. The experimental data are shown Fig 5. and Fig 6. D. Triangle Wave Motion Triangular waveforms are used to evaluate the effectiveness of the PI close-loop control that uses piezoelectric straininduced voltages as feedback signals. Fig. 7 and Fig. 8 shows the closed loop traces of triangular waveforms with - 4 Step-Train Response Test Y -axis Fig 4. step-train response, X state, and Y state Hz Hz Hz Hz Hz Y-axis Sine Wave Test X-axis Triangle Wave Test Hz Fig 7. X-axis triangle wave motion, Hz, Hz, Hz, and 5Hz Hz 5Hz Hz Fig 6. Y-axis sine wave motion, Hz, Hz, Hz, and 5Hz. 5Hz Fig 5. X-axis sine wave motion, Hz, Hz, Hz, and 5Hz

4 Hz Hz Y-axis Triangle Wave Test Fig 8. Y-axis triangle wave motion, Hz, Hz, Hz, and 5Hz. Hz 5Hz controller designed to regulate three DOFs to a precision extent and track the particular desired motion. The nano-positioner s traveling range is approximately 5μm 5μm 5μm and the fast scanning axis is optimized for speed. Finally, satisfactory performance of the precision positioning motion is obtained in the actual experiments. The experimental results reveal that the positioning performance has attained the sensor s limitary accuracy. Spiral Motion 5 Hz E. Cycling Motion The other way to show the tracking capability is to profile a desired circle. We will present the experimental results of this circling motion, given the PI controller, with the radius equal to m at frequency 5Hz.The XY plot is shown Fig 9. Cycling Motion 5 Hz Y-axis - Y-axis - - X-axis Fig 9. 5 Hz circling motion in current system: XY plot F. Spiral Motion Here, we show that our system is allowed to perform spiral trajectory tracking. We present the experimental results of the -Dimentional spiral motion at 5Hz with the final amplitude equal to m as shown in Fig. IV. CONCLUSIONS This paper described the design of a fast -dimendional nano-positioner based on piezo-stack actuators. The system is a multi-input multi-output (MIMO) system. A traditional PI - X-axis Fig. 5 Hz spiral motion in current system: XY plot V. REFERENCE [] G. Binnig, et al., "Atomic Force Microscope," Physical Review Letters, vol. 56, p. 9, 986. [] M. Sitti and H. Hashimoto, "Two-dimensional fine particle positioning using a piezoresistive cantilever as a micro/nanomanipulator," in Robotics and Automation, 999. Proceedings. 999 IEEE International Conference on, 999, pp vol.4. [] H. M. Gutierrez and P. I. Ro, "Sliding-mode control of a nonlinearinput system: application to a magnetically levitated fast-tool servo," Industrial Electronics, IEEE Transactions on, vol. 45, pp. 9-97, 998. [4] R. Luck and E. I. Agba, "On the design of piezoelectric sensors and actuators," ISA Transactions, vol. 7, pp. 65-7, 998. [5] H. Mizumoto, et al., "An angstrom-positioning system using a twist-roller friction drive," Precision Engineering, vol. 7, pp. 57-6, 995. [6] R. C. Merkle, "A new family of six degrees of freedom positional devices," Nanotechnology, vol. 8, p. 47, 997. [7] S. H. Chang and B. C. Du, "A precision piezodriven micropositioner mechanism with large travel range," Review of Scientific Instruments, vol. 69, pp , 998. [8] J. H. Kindt, et al., "Rigid design of fast scanning probe microscopes using finite element analysis," Ultramicroscopy, vol., pp , 4. [9] G. Schitter, et al., "Design and Modeling of a High-Speed AFM- Scanner," Control Systems Technology, IEEE Transactions on, vol

5 5, pp , 7. [] J. MAMIN, et al., Two-dimensional, remote micropositioner for a scanning tunneling microscope vol. 56. Woodbury, NY, ETATS- UNIS: American Institute of Physics,