A dual-purpose positioner-fixture for precision six-axis positioning and precision fixturing: Part II. Characterization and calibration

The kinematics, stiffness, and repeatability of a moving groove, dual-purpose positioner-fixture were determined experimentally. A dual-purpose positioner-fixture is an alignment device that may be operated in a fixture mode or a six-axis nanopositioning mode. When operated in fixture mode, experiments show standard deviation in repeatability of 11, 11, and 38 nm in x, y, and z; and 0.7, 0.3, and 0.3 μrad in θ_x, θ_y, and θ_z. The stiffness characteristics were shown to match predictions within 5%. When operated in nanopositioner mode, the device demonstrated 4 nm resolution and a range, of 40 μm × 40 μm × 80 μm in translation and 800 μrad × 800 μrad × 400 μrad in rotation. The fixture possesses a load capacity of 450 N and a natural frequency of 200 Hz when the fixture is preloaded to 225 N.     

Design of integrated eccentric mechanisms and exact constraint fixtures for micron-level repeatability and accuracy

This paper introduces an eccentric ball–shaft kinematic fixture which is capable of six-axis alignment corrections and thereby improved fixture accuracy. A kinematic model for an eccentric ball–shaft fixture was developed and used to simulate the effect of: (1) tolerances, (2) actuation errors and (3) bearing run out on fixture accuracy. The kinematic model and these errors were used to determine when it is practical to use the technology to improve fixture accuracy. The kinematic model was used to design a prototype whose performance matched the kinematic model to within 10%. Diagnosis of experimental data indicates that differences between theory and data may be explained through statistical analysis of error sources. The stabilized 1σ repeatability of the prototype was measured at better than 1.9 μm/3.6 μrad.     

A novel parallel-kinematics mechanisms for integrated, multi-axis nanopositioning: Part 1. Kinematics and design for fabrication

Multi-axis micro and nanopositioning systems are increasingly used in much of the metrology and process equipment related to the field of nanotechnology. This, the first of a two-part series of papers on a novel piezo-driven, parallel-kinematics XYZ nanopositioning (PKXYZNP) stage, concentrates on the development of a viable scheme to achieve pure spatial translation. First, the mechanism is shown to admit closed-form solutions to both; the forward and reverse kinematic problems. The Jacobian and the dynamics of the system indicate that the mechanical structure produces a relatively large work volume, and is capable of high bandwidth and uniform performance across it. The fabrication of the system is described along with some basic testing of its Jacobian and its modal frequencies. Using capacitive gages, the stage is capable of about 85 μm of motion along each axis with a resolution of about 2–4 nm. The controls, testing and performance are discussed in detail in the companion paper [Dong J, Yao Q, Ferreira PM. A novel parallel-kinematics mechanism for integrated, multi-axis nanopositioning. Part 2. Dynamics, control and performance analysis. Precis Eng].     

Design of quasi-kinematic couplings

A quasi-kinematic coupling (QKC) is a fixturing device that can be used to make low-cost assemblies with sub-micron precision and/or sealing contact. Unlike kinematic couplings that form small-area contacts between mating balls in v-grooves, QKCs are based on arc contacts formed by mating three balls with three axisymmetric grooves. Though a QKC is technically not an exact constraint coupling, proper design of the contacts can produce a weakly over constrained coupling that emulates an exact constraint coupling. This paper covers the practical design of QKCs and derives the theory that predicts QKC stiffness. A metric used to minimize over constraint in QKCs is presented. Experimental results are provided to show that QKCs can provide repeatability (1/4 μm) that is comparable to that of kinematic couplings.     

Characteristics of practical control for point-to-point (PTP) positioning systems: Effect of design parameters and actuator saturation on positioning performance

In this study, a nominal characteristic trajectory following (NCTF) controller for point-to-point (PTP) positioning systems is introduced and its performance is evaluated. The NCTF controller consists of a nominal characteristic trajectory (NCT) and a compensator. The objective of the NCTF controller is to make the object motion follow the NCT and end at its origin. Therefore, the NCT is used as an intended object motion and the compensator is used to make the motion of the controlled object follow the NCT. The NCTF controller is designed based on a simple open-loop experiment of the object and no information except the NCT is necessary for controller design. The effectiveness of the NCTF controller is evaluated and discussed through simulations and experiments using an experimental rotary positioning system. The effect of the design parameters on the robustness of the NCTF controller to inertia and friction variations is evaluated and the influence of saturation on the positioning performance is examined. Moreover, the effects of the saturation on the positioning performance and robustness are compared with those of conventional PID ones. It is proved that the NCTF controller is much more accurate and robust to inertia and friction variations than the PID controllers, even if the saturation occurs.     

A novel precision positioning table utilizing impact force of spring-mounted piezoelectric actuator—part I: experimental design and results

This paper proposes a novel high-precision and large-stroke positioning table utilizing the spring-mounted piezoelectric actuator. An experimental setup with the actuation along one direction in the horizontal plane was configured to elucidate the characteristics of the positioning table. Several parameters, e.g. the waveform and the amplitude of applied voltage, the mass ratio, and the stiffness of spring, which affect the motion behavior of the table were examined and discussed. The experimental results show that the proposed actuator can actuate a heavy table by utilizing the impact force of a piezoelectric element while maintaining the comparatively long operational range of the initially compressed spring.     

A simplified design approach for high-speed wind tunnels. Part I: Table of inclination

Journal of Mechanical Science and Technology - This study aims to develop a simplified approach for the design of high-speed wind tunnels, operating within the range of Mach 1-4. The study is...     

A novel parallel-kinematics mechanism for integrated, multi-axis nanopositioning: Part 2: Dynamics, control and performance analysis

In this paper, we discuss the dynamics, controls and performance of a parallel-kinematics, integrated, multi-axis nanopositioner, the PKXYZNP [Yao Q, Dong J, Ferreira PM. A novel parallel-kinematics mechanisms for integrated, multi-axis nano-positioning. Part 1: Kinematics and design for fabrications]. The paper focuses on computing the workspace of the stage, characterization of its dynamic behavior, synthesis of a controller for it, and the testing of its contour tracking and positioning performance. For this system, because of the coupled nature of the axes, a MIMO control scheme is adopted to directly close the loop around the kinematics of the stage, i.e., the position of the table/end-effector is fed back to control the actuators. This scheme has the added advantage of not requiring complex and fragile kinematic calibration of the stage as the accuracy becomes a function of only the accuracy of the sensing system and the servo performance. To make the MIMO control scheme tractable by reducing its order, the controller design is performed in the modal space of the system. A resolution of 2–4 nm is achieved from this stage. Linear and circular tests were performed to evaluate the contouring performance of the PKXYZ stage. In spite of a relatively heavy load condition (the weight of a solid target), the linear and circular contouring errors are less than 40 and 150 nm, respectively, with contouring speeds ranging up to 40 μm/s.     

A large deflection and high payload flexure-based parallel manipulator for UV nanoimprint lithography: Part I. Modeling and analyses

This paper presents a flexure-based parallel manipulator (FPM) that delivers nanometric co-planar alignment and direct-force imprinting capabilities to automate an ultra-violet nanoimprint lithography (UV-NIL) process. The FPM is articulated from a novel 3-legged prismatic-prismatic-spherical (3PPS) parallel-kinematic configuration to deliver a θ_x–θ_y–Z motion. The developed FPM achieves a positioning and orientation resolution of ±10 nm and 0 . 05″ respectively, and a continuous output force of 150 N/Amp throughout a large workspace of 5°×5°×5 mm. Part I mainly focuses on a new theoretical model that is used to analyze the stiffness characteristics of the compliant joint modules that formed the FPM, and experimental evaluations of each compliant joint module. Part II presents the stiffness modeling of the FPM, the performance evaluations of the developed prototype, and the preliminary results of the UV-NIL process.     

An Internet-based integrated product design environment. Part I: a hybrid agent and network architecture

During the past two decades, concurrent or collaborative engineering (CE) has presented new possibilities for successful product development. In addition, the advances in computer networks and information technology have brought engineering design context into a new era. As a promising approach to accommodate the radical pace of changes in the context of engineering design, agent technologies have been attracting public attention and are being used in an increasingly wide variety of applications. However, little attention has been paid to multi-agent system (MAS) frameworks for CE environments that enable systematic and timely design integrations in both hierarchical and heterarchical design topology. This is the first of a two-part paper proposing a MAS framework for integrated product design in a computer network-oriented CE environment. Part I first proposes a hybrid agent network architecture to develop lightweight, dynamic and large-scale distributed systems, and then proposes a hybrid agent architecture based on our finite state automata (FSA) formalism that can exhibit both hybrid behaviours and hybrid interactions. Finally, some ideas for building an integrated product design environment are presented using the proposed agent and network architecture. Part II discusses the applications of the proposed MAS framework to concurrent engineering design.     

A comparison of fire-resistant hydraulic fluids for hazardous industrial environments. Part I. Fire resistance and lubrication properties

Fire-resistant hydraulic fluids have been developed since the Second World War. In addition to phosphate esters, there are various other fluids (e.g. oil-in-water emulsions, water glycols) available. This paper provides a technical comparison of the different fluid types, in terms of fire resistance, lubricating properties, and viscosity. The second part of the study examines the corrosion properties, thermal and oxidative stability, shear stability, materials compatibility, and other physical properties.     

Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending. Part I: analytical models and minimum weight design

Analytical predictions are made for the three-point bending collapse strength of sandwich beams with composite faces and polymer foam cores. Failure is by the competing modes of face sheet microbuckling, plastic shear of the core, and face sheet indentation beneath the loading rollers. Particular attention is paid to the development of an indentation model for elastic faces and an elastic–plastic core. Failure mechanism maps have been constructed to reveal the operative collapse mode as a function of geometry of sandwich beam, and minimum weight designs have been obtained as a function of an appropriate structural load index. It is shown that the optimal designs for composite–polymer foam sandwich beams are of comparable weight to sandwich beams with metallic faces and a metallic foam core.     

A simple method for testing measuring machines and machine tools. Part 2: Construction details

Part 1 of this article, which appeared in the previous issue of this journal, detailed the principles and applications of magnetic ball bars. These can give rapid, precise indications of the two or three dimensional accuracy of a machine. Here, construction details are presented     

Hydroforming of aluminum extrusion tubes for automotive applications. Part I: buckling, wrinkling and bursting analyses of aluminum tubes

Three possible failure modes have been identified in tube hydroforming: buckling, wrinkling and bursting. A general theoretical framework is proposed for analyzing these failure modes as an elastoplastic bifurcation problem. This framework enables advanced yield criteria and various strain-hardening laws to be readily incorporated into the analysis. The effect of plastic deformation on the geometric instability in tube hydroforming, such as global buckling, axisymmetric wrinkling and asymmetric wrinkling, is precisely treated by using the exact plane stress moduli tensor. A mathematical formulation for predicting the localized condition for bursting failure is established herein. Furthermore, the critical conditions governing the onset of buckling, axisymmetric wrinkling and asymmetric wrinkling are derived in closed-form expressions for the critical axial compressive stresses. Closed-form solutions for the critical stress are developed based on Neale–Hutchinson's constitutive equation and an assumed deformation theory of plasticity. It is demonstrated that the onset of asymmetric wrinkling always requires a higher critical axial compressive stress than the axisymmetric one under the context of tube hydroforming with applied internal pressure and hence the asymmetric wrinkling mode can be excluded in the analysis of tube hydroforming. Parametric studies show that buckling and axisymmetric wrinkling are strongly dependent on geometric parameters such as t₀/r₀ and r₀/ℓ₀, and that axisymmetric wrinkling is the predominant mode for short tubes while global buckling occurs for long slender tubes.     

A method for assessing geometrical errors in layered manufacturing. Part 2: Mathematical modelling and numerical evaluation

Layered manufacturing based rapid prototyping processes are subjected to not only a staircase effect owing to the approximating process used, but also an accumulated error transfer between layers. Certain types of error such as surface tilting and layer thickness variations that occur in one layer can transfer to other layers above it. This paper describes a mathematical model based on the physical and geometrical models discussed in Part 1 of the paper. The model uses the matrix transformation method to analyse the effect of transformation of local errors to the multiple layer global errors. A data preparation error transformation matrix is used to describe the error interactions between layers during the data preparation stage. A disturbance error transformation matrix is used to describe the error interaction within each layer and error propagation between layers during the part building process. This model describes geometrical error analysis involving profiling error, layer inclination and layer thickness variations. Numerical evaluation of the model is carried out for a typical benchmark component.     

A method for assessing geometrical errors in layered manufacturing. Part 1: Error interaction and transfer mechanisms

Geometric accuracy of components is one of the most important quality characteristics in layered manufacturing processes on which most rapid prototyping (RP) techniques are based. Layered manufacturing is an approximate fabricating process in which the final geometric error of the physical part is affected, not only by the approximation technique used, but also by the fabrication process. Errors that occur in one layer could propagate and transfer to other layers causing an accumulated error effect in the process. In this paper, a concept of disturbance error is introduced to describe the effect of accumulated errors in the fabrication process. A physical model is presented to describe error interactions and error transfer mechanisms in the layered manufacturing process. A geometrical model is developed using surface approximation techniques to describe the relationships of the geometrical errors. It is shown that although the complexity of the part geometry is not directly related to the manufacturing process, it will affect the geometrical errors of the part produced.     

A large deflection and high payload flexure-based parallel manipulator for UV nanoimprint lithography: Part II. Stiffness modeling and performance evaluation

This paper presents a flexure-based parallel manipulator (FPM) that delivers nanometric co-planar alignment and direct-force imprinting capabilities to automate an ultra-violet nanoimprint lithography (UV-NIL) process. The FPM is articulated from a 3-legged Prismatic-Prismatic-Spherical (3PPS) parallel-kinematic configuration to deliver a θ_x–θ_y–Z motion. The developed FPM achieves a positioning and orientation resolution of ±10 nm and 0.05″, respectively, and a continuous output force of 150 N/A throughout a large workspace of 5°×5°×5 mm. Part I mainly focuses on a new theoretical model that is used to analyze the stiffness characteristics of the compliant joint modules that formed the FPM, and experimental evaluations of each compliant joint module. Part II presents the stiffness modeling of the FPM, the performance evaluations of the developed prototype, and the preliminary results of the UV-NIL process.