The design and full closed-loop controls of micro/nano positioning system are presented in this paper. The micro/nano positioning system mainly consists of a 3-DOF compliant mechanism, a micro-vision system and three piezoelectric actuators. In order to compensate for nonlinear hysteresis in the piezoelectric actuators, an adaptive controller using direct inverse modeling approach based on a modified Prandtl–Ishlinskii model is presented. Instead of using traditional displacement sensors, a micro-vision system (MVS) is used to obtain feedback signals online. Based on the micro-vision system, a full closed-loop tracking control is developed to enhance the positioning accuracy of micro/nano positioning system. Taking into account the coupling motions, another full closed-loop tracking control with a decoupling feedforward controller is also proposed. Experimental results demonstrate that the full closed-loop controls can improve the positioning accuracy when compared with an open-loop control. Furthermore, the decoupling feedforward controller can improve the tracking performance of full closed-loop tracking control as well.

Full closed-loop controls of micro/nano positioning system with nonlinear hysteresis using micro-vision system

This paper presents the design and testing of a novel 3-DOF parallel flexure micropositioning stage for micro-scale operations. The proposed modular design can obtain the merit of high interchangeability during maintenance process. The output platform of the mechanism offers pure translational motion along X, Y, and Z axes by resorting to the flexure guiding of two parallelogram joints. Meanwhile, the output motion is decoupled by using two leaves with symmetric ellipse-shaped flexure hinges, and the platform provides isolated movement without parasitic motion. By using the bridge-type and lever-type compound amplifier, the micropositioning stage provides a large output displacement, which is over 30 times the input displacement provided by piezoelectric actuator. The enlarged displacement is translated to the orthogonal parallel mechanism by four straight beams, which provide perfect decoupling properties. In addition, the modular design principle makes it possible to adopt multiple materials to balance the performance of the actuator and decoupling flexure hinges. Analytical analysis and finite element analysis simulation are conducted to verify the fine decoupling property and large translational motion of the proposed 3-DOF parallel micropositioning stage. Moreover, a prototype is fabricated using multiple materials for experimental testing. Results demonstrate the promising performance of the developed decoupled micropositioning stage.

Design and testing of a new 3-DOF spatial flexure parallel micropositioning stage

Experimental validation of the kinematic design of 3-PRS compliant parallel mechanisms

Parallel manipulators, especially those with outputs as a translation and two rotations (1T2R), are being increasingly studied. The 3PRS mechanism is a very typical example of this category, but it has peculiar kinematic characteristics caused by parasitic motions and by low orientation capability. To overcome these problems, new mechanisms are being studied, such as the 2PRU-1PRS manipulator. As in the case of the 3PRS manipulator, the degrees of freedom of the 2PRU-1PRS are one translation along the Z-axis and two rotations about the X- and Y-axes. The advantages are that the parasitic motion appears only in one direction instead of in three and that the orientation capability is higher. In this paper we solve the kinematics, singularities and dynamics of a 2PRU-1PRS mechanism. We first analyse a general 2PRU-1PRS mechanism and then present the results for the particular case of the 2PRU-1PRS used for automobile pieces testing purposes.

Analysis of the 2PRU-1PRS 3DOF parallel manipulator: kinematics, singularities and dynamics

Kinematic analysis and comparison of a 2R1T redundantly actuated parallel manipulator and its non-redundantly actuated forms

Explicit Dynamic equations are needed for simulation and control in the field of Mechatronics. Several classical methods are available to get Dynamic equations. Regarding those methods that aim exclusively at the equations relating applied torques and motion generated, i.e. avoiding any calculus of joint wrenches, Analytical mechanics offers several approaches. For serial mechanisms, Lagrange equations are very convenient and systematic. However, finding such mathematical expressions can be cumbersome when facing closed-loop mechanisms even with the help of Lagrange multipliers. Moreover, this is quite complex if spatial rotations are considered, and hence, generalized coordinates are very much coupled in the expressions of Lagrange functions to be differentiated. Boltzmann-Hamel equations come to help in this regard. In this paper, authors show the finding of the dynamic equations of the $3\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{P} RS$ lower-mobility parallel manipulator using the Boltzmann-Hamel equations and exploring the effect of coupled freedoms in the rotation of the end-effector.

Dynamic Modelling of Lower-Mobility Parallel Manipulators Using the Boltzmann-Hamel Equations

Mechatronic modeling of a parallel kinematics multi-axial simulation table based on decoupling the actuators and manipulator dynamics

Parallel manipulators, compared to serial manipulators, have some interesting properties, such as high stiffness, low inertia, high velocity, good accuracy and large payload capacity. Thus, parallel manipulators, especially the ones with one translation and two rotations as outputs (1T2R), are being increasingly studied. The 3PRS mechanism is a very typical example of this category, but it has accuracy problems caused by the parasitic motion, and low orientation capability. To overcome these problems, new mechanisms are being studied, such as the 2PRU-1PRS manipulator. As the 3PRS manipulator, the degrees of freedom of the 2PRU-1PRS are one translation along the Z-axis and two rotations about the X- and Y-axes. The advantages are that the parasitic motion appears only in one direction instead of in three and that the orientation capability is higher. In this paper we present the design of a 2PRU-1PRS mechanism suitable for vibration tests. In order to do this, we develop a code with an intuitive GUI (graphical user interface) that, for given variable limits, solves the inverse kinematic and dynamic problem for all the variable combinations and obtains the combination that consumes less power for an harmonic trajectory. Taking the simulations results into account, we propose a design that fulfils all the requirements for vibration tests in the three axes.Copyright © 2014 by ASME

Analysis and Design of the 2PRU-1PRS Manipulator for Vibration Testing

In this paper, authors show the results of performance simulation of a 3PRS lower-mobility parallel manipulator actuated by electronic devices. The simulation includes a mechatronic model of the actuators, the dynamic response of the mechanism found using the Boltzmann-Hamel equations, and a model of the control. The dynamics of the actuators is modelled using two transfer functions found by means of a test based identification method. Authors find the explicit Dynamic equations needed for simulation using analytical mechanics. Lagrange equations are convenient and systematic in open-loop serial kinematic chains. However, for closed-loop mechanisms are cumbersome, even with the help of Lagrange multipliers. Moreover, if spatial rotations are involved, generalized coordinates are very much coupled in the expressions of Lagrange functions to be differentiated. Boltzmann-Hamel equations come to help in this regard. By using Simulink, authors could evaluate the stability of the control and the bandwidth of the manipulator.Copyright © 2015 by ASME

Constantino Roldan-Paraponiaris

Papers

Experimental validation of the kinematic design of 3-PRS compliant parallel mechanisms

Dynamic Modelling of Lower-Mobility Parallel Manipulators Using the Boltzmann-Hamel Equations

Mechatronic modeling of a parallel kinematics multi-axial simulation table based on decoupling the actuators and manipulator dynamics

Analysis and Design of the 2PRU-1PRS Manipulator for Vibration Testing

Dynamic Simulation of a Tripod Based in Boltzmann-Hamel Equations