Conceptual designs of multi-degree of freedom compliant parallel manipulators composed of wire-beam based compliant mechanisms

This paper proposes conceptual designs of multi-degree(s) of freedom (DOF) compliant parallel manipulators (CPMs) including 3-DOF translational CPMs and 6-DOF CPMs using a building block based pseudo-rigid-body-model (PRBM) approach. The proposed multi-DOF CPMs are composed of wire-beam based compliant mechanisms (WBBCMs) as distributed-compliance compliant building blocks (CBBs). Firstly, a comprehensive literature review for the design approaches of compliant mechanisms is conducted, and a building block based PRBM is then presented, which replaces the traditional kinematic sub-chain with an appropriate multi-DOF CBB. In order to obtain the decoupled 3-DOF translational CPMs (XYZ CPMs), two classes of kinematically decoupled 3-PPPR (P: prismatic joint, R: revolute joint) translational parallel mechanisms (TPMs) and 3-PPPRR TPMs are identified based on the type synthesis of rigid-body parallel mechanisms, and WBBCMs as the associated CBBs are further designed. Via replacing the traditional actuated P joint and the traditional passive PPR/PPRR sub-chain in each leg of the 3-DOF TPM with the counterpart CBBs (i.e. WBBCMs), a number of decoupled XYZ CPMs are obtained by appropriate arrangements. In order to obtain the decoupled 6-DOF CPMs, an orthogonally-arranged decoupled 6-PSS (S: spherical joint) parallel mechanism is first identified, and then two example 6-DOF CPMs are proposed by the building block based PRBM method. It is shown that, among these designs, two types of monolithic XYZ CPM designs with extended life have been presented

A novel actuator-internal micro/nano positioning stage with an arch-shape bridge type amplifier

This paper presents a novel actuator-internal two degree-of-freedom (2-DOF) micro/nano positioning stage actuated by piezoelectric (PZT) actuators, which can be used as a fine actuation part in dual-stage system. To compensate the positioning error of coarse stage and achieve a large motion stroke, a symmetrical structure with an arch-shape bridge type amplifier based on single notch circular flexure hinges is proposed and utilized in the positioning stage. Due to the compound bridge arm configuration and compact flexure hinge structure, the amplification mechanism can realize high lateral stiffness and compact structure simultaneously, which is of great importance to protect PZT actuators. The amplification mechanism is integrated into the decoupling mechanism to improve compactness, and to produce decoupled motion in X- and Y- axes. An analytical model is established to explore the static and dynamic characteristics, and the geometric parameters are optimized. The performance of the positioning stage is evaluated through finite element analysis (FEA) and experimental test. The results indicate that the stage can implement 2-DOF decoupled motion with a travel range of 55.4×53.2 μm2, and the motion resolution is 8 nm. The stage can be used in probe tip-based micro/nano scratching

An inverse Prandtl–Ishlinskii model based decoupling control methodology for a 3-DOF flexure-based mechanism

A modified Prandtl–Ishlinskii (P–I) hysteresis model is developed to form the feedforward controller for a 3-DOF flexure-based mechanism. To improve the control accuracy of the P–I hysteresis model, a hybrid structure that includes backlash operators, dead-zone operators and a cubic polynomial function is proposed. Both the rate-dependent hysteresis modeling and adaptive dead-zone thresholds selection method are investigated. System identification was used to obtain the parameters of the newly-developed hysteresis model. Closed-loop control was added to reduce the influence from external disturbances such as vibration and noise, leading to a combined feedforward/feedback control strategy. The cross-axis coupling motion of the 3-DOF flexure-based mechanism has been explored using the established controller. Accordingly, a decoupling feedforward/feedback controller is proposed and implemented to compensate the coupled motion of the moving platform. Experimental tests are reported to examine the tracking capability of the whole system and features of the controller. It is demonstrated that the proposed decoupling control methodology can distinctly reduce the coupling motion of the moving platform and thus improve the positioning accuracy and trajectory tracking capability

Micro position control of a designed 3-PRR compliant mechanism using experimental models

A new compliant stage based on 3-PRR kinematic structure is designed to be used as a planar micro positioner. The mechanism is actuated by using piezoelectric actuators and center position of the stage is measured using a dual laser position sensor. It's seen that manufactured mechanism has unpredictable motion errors due to manufacturing and assembly faults. Thus, sliding mode control with disturbance observer is chosen to be implemented as position control in x-y axes of the center of the mechanism. Instead of piezoelectric actuator models, experimental models are extracted for each actuation direction in order to be used as nominal plants for the disturbance observer. The position control results are compared with the previous position control using linear piezoelectric actuator models and it's seen that the implemented control methodology is better in terms of errors in x and y axes. Besides, the position errors are lowered down to ±0.06 microns, which is the accuracy of the dual laser position sensor

DETC2005/MECH-85241 DYNAMIC MODELING AND CONTROLLER DESIGN OF A PLANAR PARALLEL 3-RRR COMPLIANT MICROMANIPULATOR

ABSTRACT This paper presents control system formulations of a planar parallel 3-RRR parallel compliant micromanipulator. The design methodology is illustrated with one of such designs constructed at Beijing University of Aeronautics and Astronautics, China. Compliant joints and motion-amplifying mechanism allow rapid and accurate response as well as larger workspace. The three PZT actuators attached on the linkages produce the bending moments. The sensor is a CCD camera feeding back the tool point position. The plant is the equations of motion which can be formulated using the Lagrangian method and dynamics software. The system dynamic model was developed with ADAMS which can export the nonlinear and linearized control plant to Matlab Simulink. Overall dynamic behavior of the manipulator will be illustrated through simulations with Matlab Simulink Toolbox. After comparison of two different control plans, the controller obtained from LQR method was chosen to achieve the control objectives. Closed-loop performance in response to a step reference was plotted. Bode plots of the sensitivity and complementary sensitivity showed their relation to the step response. Gain and phase margins was computed

A 2 degree-of-freedom SOI-MEMS translation stage with closed loop positioning

This research contains the design, analysis, fabrication, and characterization of a closed loop XY micro positioning stage. The XY micro positioning stage is developed by adapting parallel-kinematic mechanisms, which have been widely used for macro and meso scale positioning systems, to silicon-based micropositioner. Two orthogonal electrostatic comb drives are connected to moving table through 4-bar mechanism and independent hinges which restrict unwanted rotation in 2-degree-of-freedom translational stage. The XY micro positioning stage is fabricated on SOI wafer with three photolithography patterning processes followed by series of DRIE etching and HF etching to remove buried oxide layer to release the end-effector of the device. The fabricated XY micro positioning stage is shown in Fig1 with SEM images. The device provides a motion range of 20 microns in each direction at the driving voltage of 100V. The resonant frequency of the XY stage under ambient conditions is 811 Hz with a high quality factor of 40 achieved from parallel kinematics. The positioning loop is closed using a COTS capacitance-to-voltage conversion IC and a PID controller built in D-space is used to control position with an uncertainty characterized by a standard distribution of 5.24nm and a approximate closed-loop bandwidth of 27Hz. With the positioning loop, the rise time and settling time for closed-loop system are 50ms and 100ms. With sinusoidal input of ω=1Hz, the maximum phase difference of 108nm from reference input is obtained with total motion range of 8μm

Design and optimization of full decoupled micro/nano-positioning stage based on mathematical calculation

Nano-positioning is widely used in Micro-electromechanical Systems (MEMS), micromanipulator and biomedicine, coupling errors and tiny output displacements are the main disadvantages of the one. A totally uncoupled micro/nano-positioning stage with lever amplifiers is designed and tested in this paper. It is fully symmetrical along with the x- and y-directions. For obtaining large output displacements, two fully symmetric two-stage lever displacement amplifiers are utilized to amplify output displacements of piezoelectric actuators (PZTs). The established models for performances evaluation of the stage, in terms of kinetostatics, amplification ratio, reachable workspace, the input and output stiffness, are verified by finite element analysis (FEA). After that, the dimensional optimization is also carried out through the genetic optimization algorithm.The prototype of the mechanism is fabricated by using Wire-Electrical-Discharge-Machining (WEDM) process. Testing results indicate that the proposed micromanipulator demonstrates good performance.</p