Yanling Tian

A Novel Direct Inverse Modeling Approach for Hysteresis Compensation of Piezoelectric Actuator in Feedforward Applications

The Prandtl-Ishlinskii (PI) model is widely utilized in hysteresis modeling and compensation of piezoelectric actuators. For systems with rate-independent hysteresis, the inverse PI model is analytically feasible and it can be adopted as a feedforward compensator for the hysteretic nonlinearity of piezoelectric actuators. However, for the rate-dependent PI model, the applicable valid inversion methodology is not yet available. Although simply replacing all the rate-independent terms in the conventional inversion law with the rate-dependent terms can achieve acceptable results at very slow trajectories. However, a large theoretical modeling error is inevitable at fast trajectories, which is investigated through simulations. This paper proposes a new direct approach to derive the inverse PI model directly from experimental data. As no inversion calculation is involved, the proposed direct approach is efficient and the theoretical modeling error can be avoided. In order to validate the accuracy of the direct approach, a number of experiments have been implemented on a piezo-driven compliant mechanism by utilizing the inverse PI model as a feedforward controller. The tracking performance of the mechanism is significantly improved by the direct approach.

Design and Computational Optimization of a Decoupled 2-DOF Monolithic Mechanism

This paper presents the mechanical design, computational optimization, and experimentation of a decoupled 2-DOF monolithic mechanism. In the mechanical design, statically indeterminate leaf parallelograms provide the decoupling effect, and the displacement of the piezoelectric actuator (PEA) is amplified with a statically indeterminate lever mechanism. In a piezo-driven mechanism, the contact interface between the PEA and the mechanism is a major cause of the discrepancies between the estimated and measured characteristics. However, no explicit and reliable model is available to estimate the contact stiffness. In this paper, a computational optimization based on the response surface methodology is performed and the influence of the contact interface is taken into consideration by adding adequate safety margin to the design objectives. Ultimately, a prototype is manufactured and experimentally investigated for its characteristics and performances. Experimental results show that the developed mechanism has a workspace range in excess of 82 μm × 82 μm with a first natural frequency of 423 Hz (with a 53.4-g load mass). The cross-axis coupling ratio is experimentally measured to be below 1%, indicating excellent decoupling performances.

Design of a Piezoelectric-Actuated Microgripper With a Three-Stage Flexure-Based Amplification

This paper presents a novel microgripper mechanism for micromanipulation and assembly. The microgripper is driven by a piezoelectric actuator, and a three-stage flexure-based amplification has been designed to achieve large jaw displacements. The kinematic, static and dynamic models of the microgripper have been established and optimized considering the crucial parameters that determine the characteristics of the microgripper. Finite element analysis was conducted to evaluate the characteristics of the microgripper, and wire electro discharge machining technique was utilized to fabricate the monolithic structure of the microgripper mechanism. Experimental tests were carried out to investigate the performance of the microgripper and the results show that the microgripper can grasp microobjects with the maximum jaw motion stroke of 190 μm corresponding to the 100-V applied voltage. It has an amplification ratio of 22.8 and working mode frequency of 953 Hz.

Experimental Investigation of Robust Motion Tracking Control for a 2-DOF Flexure-Based Mechanism

The design, parameter identification and robust motion tracking control of a two degree of freedom (2-DOF) flexure-based micro/nanomechanism are presented in this paper. In the presented compliant mechanism, the cross-axis coupling ratio is below 1% indicating excellent decoupling performance. Despite this, during motion tracking the cross coupling effect cannot be ignored. To enhance the accuracy of micro/nanomanipulation, a laser interferometry-based sensing and measurement system is established. Nonlinearities such as creep/drift and hysteresis are present in this system, which are compensated with closed-loop control. Open-loop tracking results for a 1-DOF trajectory, with and without cross-axis coupling compensation are also presented. Robust motion tracking control is extended to support 2-DOF motion trajectories. This controller is implemented to track the desired trajectories over one and two axes of motion. Robust motion control demonstrates high precision and accurate motion tracking of the 2-DOF flexure-based mechanism. The cross-axis coupling is treated as a known disturbance and the performance of tracking 1-DOF trajectory, with and without cross-axis coupling compensation, is presented. Circular motion trajectories with radii of 10 μm, 1 μm, and 250 nm are also tracked. The experimental results presented in this paper demonstrate effective compensation of the cross-axis coupling with high precision motion tracking. The resultant 2-DOF closed-loop position tracking error in the X and Y axes are within ±20 nm during dynamic motion, and ±8 nm in the steady state.

A novel flexure-based microgripper with double amplification mechanisms for micro/nano manipulation

This paper describes the design, modeling, and testing of a novel flexure-based microgripper for a large jaw displacement with high resolution. Such a microgripper is indispensable in micro∕nano manipulation. In achieving a large jaw displacement, double amplification mechanisms, namely, Scott-Russell mechanism and leverage mechanism arranged in series, are utilized to overcome the limited output of microgrippers driven by piezoelectric actuators. The mechanical performance of the microgripper is analyzed using the pseudo rigid body model approach. Finite element analysis is conducted to evaluate the performance and validate the established models for further optimum design of the microgripper. The prototype of the developed microgripper is fabricated, with which experimental tests are carried out. The experimental results show that the developed microgripper is capable of handling various sized micro-objects with a maximum jaw displacement of 134 μm and a high amplification ratio of 15.5.

An Improved Adaptive Genetic Algorithm for Image Segmentation and Vision Alignment Used in Microelectronic Bonding

In order to improve the precision and efficiency of microelectronic bonding, this paper presents an improved adaptive genetic algorithm (IAGA) for the image segmentation and vision alignment of the solder joints in the microelectronic chips. The maximum between-cluster variance (OTSU) threshold segmentation method was adopted for the image segmentation of microchips, and the IAGA was introduced to the threshold segmentation considering the features of the images. The performance of the image segmentation was investigated by computational and experimental tests. The results show that the IAGA has faster convergence and better global optimality compared with standard genetic algorithm (SGA), and the quality of the segmented images becomes better by using the OTSU threshold segmentation method based on IAGA. On the basis of moment invariant approach, the microvision alignment was realized. Experiments were carried out to implement the microvision alignment of the solder joints in the microelectronic chips, and the results indicate that there are no alignment failures using the OTSU threshold segmentation method based on IAGA, which is superior to the OTSU method based on SGA in improving the precision and speed of the vision alignments.

Development of novel hybrid flexure-based microgrippers for precision micro-object manipulation

This paper describes the process of developing a microgripper that is capable of high precision and fidelity manipulation of micro-objects. The design adopts the concept of flexure-based hinges on its joints to provide the rotational motion, thus eliminating the inherent nonlinearities associated with the application of conventional rigid hinges. A combination of two modeling techniques, namely, pseudorigid body model and finite element analysis was utilized to expedite the prototyping procedure, which leads to the establishment of a high performance mechanism. A new hybrid compliant structure integrating cantilever beam and flexural hinge configurations within microgripper mechanism mainframe has been developed. This concept provides a novel approach to harness the advantages within each individual configuration while mutually compensating the limitations inherent between them. A wire electrodischarge machining technique was utilized to fabricate the gripper out of high grade aluminum alloy (Al 7075T6). Experimental studies were conducted on the model to obtain various correlations governing the gripper performance as well as for model verification. The experimental results demonstrate high level of compliance in comparison to the computational results. A high amplification characteristic and maximum achievable stroke of 100 microm can be achieved.

A novel monolithic piezoelectric actuated flexure-mechanism based wire clamp for microelectronic device packaging

A novel monolithic piezoelectric actuated wire clamp is presented in this paper to achieve fast, accurate, and robust microelectronic device packaging. The wire clamp has compact, flexure-based mechanical structure and light weight. To obtain large and robust jaw displacements and ensure parallel jaw grasping, a two-stage amplification composed of a homothetic bridge type mechanism and a parallelogram leverage mechanism was designed. Pseudo-rigid-body model and Lagrange approaches were employed to conduct the kinematic, static, and dynamic modeling of the wire clamp and optimization design was carried out. The displacement amplification ratio, maximum allowable stress, and natural frequency were calculated. Finite element analysis (FEA) was conducted to evaluate the characteristics of the wire clamp and wire electro discharge machining technique was utilized to fabricate the monolithic structure. Experimental tests were carried out to investigate the performance and the experimental results match well with the theoretical calculation and FEA. The amplification ratio of the clamp is 20.96 and the working mode frequency is 895 Hz. Step response test shows that the wire clamp has fast response and high accuracy and the motion resolution is 0.2 μm. High speed precision grasping operations of gold and copper wires were realized using the wire clamper.

Laser-Based Sensing, Measurement, and Misalignment Control of Coupled Linear and Angular Motion for Ultrahigh Precision Movement

This paper presents a novel methodology for position and orientation (pose) measurement of stages used for micro/nano positioning which produce coupled motions with three planar degrees of freedom (DOF). In the proposed methodology, counter-rotation of the entire mechanism prevents the misalignment of the measurement beams within a laser-interferometry-based sensing and measurement technique. To detect such a misalignment, a sensing strategy constructed around a position sensitive diode has been developed. A feedforward-feedback compound controller has been established to provide the necessary counter-rotation input to reduce the misalignment error. Experimental validation has been conducted through the measurement of the workspace of a three-DOF planar micro/nano positioning stage. Experimental results demonstrate the capability of the technique to provide combined linear/angular measurement.

A novel voice coil motor-driven compliant micropositioning stage based on flexure mechanism

This paper presents a 2-degrees of freedom flexure-based micropositioning stage with a flexible decoupling mechanism. The stage is composed of an upper planar stage and four vertical support links to improve the out-of-plane stiffness. The moving platform is driven by two voice coil motors, and thus it has the capability of large working stroke. The upper stage is connected with the base through six double parallel four-bar linkages mechanisms, which are orthogonally arranged to implement the motion decoupling in the x and y directions. The vertical support links with serially connected hook joints are utilized to guarantee good planar motion with heavy-loads. The static stiffness and the dynamic resonant frequencies are obtained based on the theoretical analyses. Finite element analysis is used to investigate the characteristics of the developed stage. Experiments are carried out to validate the established models and the performance of the developed stage. It is noted that the developed stage has the capability of translational motion stroke of 1.8 mm and 1.78 mm in working axes. The maximum coupling errors in the x and y directions are 0.65% and 0.82%, respectively, and the motion resolution is less than 200 nm. The experimental results show that the developed stage has good capability for trajectory tracking.