Jianbin Zhang

A two degree of freedom micro-gripper with grasping and rotating functions for optical fibers assembling

In this paper, a two degree of freedom flexure-based micro-gripper is proposed and applied in the complicated assembling process of optical fibers. The design concept is modeled on the manipulation of human fingers. Therefore, the two tips of micro-gripper, just like human fingers, can easily grasp the optical fiber with a controllable force and precisely rotate it by the rubbing operation. In addition, some sensors installed on the micro-gripper can enhance the operating accuracy. In the developing process, pseudo-rigid-body model method and virtual work principle are employed to conduct theoretical design. Then the obtained theoretical model is validated and optimized by the finite element analysis. Fabrication of the micro-gripper adopts wire electro discharge machining technology and material of aluminum alloy (AL-7075). Experimental studies are carried out on the prototype to further validate the performance of micro-gripper. Experimental results indicate that the developed micro-gripper can well satisfy the requirements of our mission, which also means that it can be widely used in micro-manipulation field.

A parallelogram-based compliant remote-center-of-motion stage for active parallel alignment.

Parallel alignment stage with remote-center-of-motion (RCM) is of key importance in precision out-of-plane aligning since it can eliminate the harmful lateral displacement generated at the output platform. This paper presents the development of a parallelogram-based compliant RCM stage for active parallel alignment. Different from conventional parallelogram-based RCM mechanism, the proposed stage is designed with compliant mechanisms, which endows the stage with many attractive merits when used in precision micro-/nanomanipulations. A symmetric double-parallelogram mechanism (SDPM) based on flexure hinges is developed as the rotary guiding component to realize desired RCM function. Due to the geometrical constraint of the SDPM, the operating space of the stage can be easily adjusted by bending the input links without loss of rotational precision. The stage is driven by a piezoelectric actuator and its output motion is measured by non-contact displacement sensors. Based on pseudo-rigid-body simplification method, the analytical models predicting kinematics, statics, and dynamics of the RCM stage have been established. Besides, the dimensional optimization is conducted in order to maximize the first resonance frequency of the stage. After that, finite element analysis is conducted to validate the established models and the prototype of the stage is fabricated for performance tests. The experimental results show that the developed RCM stage has a rotational range of 1.45 mrad while the maximum center shift of the RCM point is as low as 1 μm, which validate the effectiveness of the proposed scheme.

Design, modeling, and simulation of a 2-DOF microgripper for grasping and rotating of optical fibers

Aiming at the micro-assembly of optical fibers, a novel 2-DOF microgripper with an asymmetric structure is proposed. Compared with conventional microgrippers, the proposed one can achieve multi-finger operations of grasping and rotating. In this paper the design of the whole device is presented. And the kinetostatic and dynamic modeling of the gripper are established using the pseudo-rigid-body model method. In order to validate the performance and optimize the design of the gripper, finite element analysis (FEA) is conducted. The simulation results indicate that: 1) the maximum stress in the microgripper is much smaller than the critical stress for fatigue; 2) with the proper amplification ratio and the stroke of the piezoelectric actuator (PZT), the grasping displacement of the designed gripper can reach 180 μm, and the optical fiber with 100 μm in diameter can be rotated by a maximum angle of 90°, which has great potential in applications.

Design of compliant parallel mechanism for Nanoimprint Lithography

Nanoimprint Lithography (NIL) is an emerging alternative lithography technology that can be repeated to print nanometer-scale geometries which have very good uniformity and repeatability. The compliant mechanism is a novel mechanism which has been utilized in many accurate mechanisms and precise instruments because of its obvious advantages such as easy assembly, zero friction, zero lubrication, low cost, monolithic manufacturing and reduced weight, etc. This paper mainly introduces the application of compliant mechanisms in NIL and analysis and design of several novel compliant mechanisms.

Design of a novel passive flexure-based mechanism for microelectromechanical system optical switch assembly

In microelectromechanical system (MEMS) optical switch assembly, the collision always exists between the optical fiber and the edges of the U-groove due to the positioning errors between them. It will cause the irreparable damage since the optical fiber and the silicon-made U-groove are usually very fragile. Typical solution is first to detect the positioning errors by the machine vision or high-resolution sensors and then to actively eliminate them with the aid of the motion of precision mechanisms. However, this method will increase the cost and complexity of the system. In this paper, we present a passive compensation method to accommodate the positioning errors. First, we study the insertion process of the optical fiber into the U-groove to analyze all possible positioning errors as well as the conditions of successful insertion. Then, a novel passive flexure-based mechanism based on the remote center of compliance concept is designed to satisfy the required insertion condition. The pseudo-rigid-body-model method is utilized to calculate the stiffness of the mechanism along the different directions, which is verified by finite element analysis (FEA). Finally, a prototype of the passive flexure-based mechanism is fabricated for performance tests. Both FEA and experimental results indicate that the designed mechanism can be used to the MEMS optical switch assembly.

Thermal performance analysis for the machine tool's spindle

The thermal deformations of a machine tool spindle system are the main factors that affect machine tool precision. In this paper, the temperature field, steady temperature distribution, transient temperature distribution and thermal error is simulated using the finite element analysis. The result provides the way to control the thermal error.

Design of a novel rotary micropositioning stage with remote center of motion characteristic

High precision rotational alignment is of key importance in micro/nanopositioning or micromanipulating applications. This paper presents a novel rotary micropositioning stage with remote center of motion (RCM) characteristic. Compared with conventional rotary guiding mechanism, the proposed double-parallelogram mechanism (DPM) possesses pure rotational motion along with a compact structure. Based on the DPM, a compact rotary micropositioning stage with RCM characteristic is then proposed. The operating space of the stage can be enlarged by adjusting the input angle without any loss of precision. And the center shift of the stage is kept in a small level due to the pure rotation motion of the DPM. Pseudo-rigid-body (PRB) method is employed to preliminarily model the kinematics and dynamics of the system. The analytical model is validated by conducting finite-element analysis (FEA). Both the analytical model and FEA results have confirmed the effectiveness of the design, which indicates that the proposed mechanism can meet the requirements for micromanipulations or precision aligning applications.

Tension Analysis for a Cable-Driven 7-DOF Manipulator

A 7-DOF cable-driven manipulator is analyzed in the paper. First, according to the torque equilibrium, a static equation of the manipulator is deduced. Then, a dynamic formulation based on the static equation is followed, which includes the influence of external torque, gravity torque, inertial torque and gyroscopic torque. And then, an effective approach of calculating the external torque, gravity torque, inertial torque, gyroscopic torque and cable tension is obtained, which is simple to compute and its physical meaning is definite. Finally, the correctness of cable tension algorithm is testified by the simulation studies. Also, the elastic distortions of cables caused by cable tensions make the manipulator departure from its ideal trajectory and an error compensation is needed.

Development of a flexure-based XY positioning stage for micro/nano manipulation

This paper presents the design and modeling methodologies of a novel flexure-based positioning stage with capable of traveling along two translational directions. A 4-PP parallel configuration is utilized to implement two planar translational motions. Each prismatic joint is achieved using a translational flexure hinge with a large deformation for smooth motion. The two layers are assembled in a top-down and stacked manner for a compact structure. Furthermore, the flexure-based stage has a totally decoupled kinematic characteristic in theory, which is crucial in micro/nano scale manipulation. Classical beam theory is utilized to conduct the statics, stiffness and dynamics modeling to predict the primary response of the flexure-based stage. Finite element analysis (FEA) is performed to examine the mechanical performances and validate the established models. The finite element simulation shows that the proposed flexure-based stage can achieve a large displacement within the millimeter level, and high natural frequencies of about 134 Hz for two translational vibrations.

A flexure-based 3-DOF parallel mechanism for optical fiber assembly

In order to bring down the cost of fiber assembly, passive method is prior to be adopted in compensation of offsets caused by positioning errors and dimensional tolerances. According to this method, this paper presents a three degree-of-freedom (DOF) planar compliant mechanism based on RCC (Remote Center of Compliance) concept. The structure of the mechanism is composed of two parts each consist of three parallel legs re-spectively, and these two components are arranged in series. In the case of passive application, compliance is mainly concerned. Therefore, theoretical calculation is imperative. This paper mainly uses pseudo-rigid-body-model (PRBM) methodology to calculate the stiffness of the mechanism. To verify the effectiveness of the theoretical model, finite element simulation is conducted. For sake of stability of the mechanism, natural frequency analysis is performed by using finite element software ANSYS.