3 research outputs found
A planar 3-DOF nanopositioning platform with large magnification
AbstractPiezo-actuated flexure-based precision positioning platforms have been widely used in micro/nano manipulation. A conventional major challenge is the trade-off between high rigidity, large magnification, high-precision tracking, and high-accuracy positioning. A compact planar three-degrees-of-freedom (3-DOF) nanopositioning platform is described in which three two-level lever amplifiers are arranged symmetrically to achieve large magnification. The parallel-kinematic configuration with optimised sizes increases the rigidity. Displacement loss models (DLM) are proposed for the external preload port of the actuator, the input port of the platform and the flexible lever mechanism. The kinematic and dynamic modelling accuracies are improved by the compensation afforded by the three DLMs. Experimental results validate the proposed design and modelling methods. The proposed platform possesses high rigidity, large magnification, high-precision circle tracking and high-accuracy positioning
Affordable flexible hybrid manipulator for miniaturised product assembly
Miniaturised assembly systems are capable of assembling parts of a few millimetres in size with an accuracy of a few micrometres. Reducing the size and the cost of such a system while increasing its flexibility and accuracy is a challenging issue. The introduction of hybrid manipulation, also called coarse/fine manipulation, within an assembly system is the solution investigated in this thesis. A micro-motion stage (MMS) is designed to be used as the fine positioning mechanism of the hybrid assembly system. MMSs often integrate compliant micro-motion stages (CMMSs) to achieve higher performances than the conventional MMSs. CMMSs are mechanisms that transmit an output force and displacement through the deformation of their structure. Although widely studied, the design and modelling techniques of these mechanisms still need to be improved and simplified. Firstly, the linear modelling of CMMSs is evaluated and two polymer prototypes are fabricated and characterised. It is found that polymer based designs have a low fabrication cost but not suitable for construction of a micro-assembly system. A simplified nonlinear model is then derived and integrated within an analytical model, allowing for the full characterisation of the CMMS in terms of stiffness and range of motion. An aluminium CMMS is fabricated based on the optimisation results from the analytical model and is integrated within an MMS. The MMS is controlled using dual-range positioning to achieve a low-cost positioning accuracy better than 2µm within a workspace of 4.4×4.4mm2. Finally, a hybrid manipulator is designed to assemble mobile-phone cameras and sensors automatically. A conventional robot manipulator is used to pick and place the parts in coarse mode while the aluminium CMMS based MMS is used for fine alignment of the parts. A high-resolution vision system is used to locate the parts on the substrate and to measure the relative position of the manipulator above MMS using a calibration grid with square patterns. The overall placement accuracy of the assembly system is ±24µm at 3σ and can reach 2µm, for a total cost of less than £50k, thus demonstrating the suitability of hybrid manipulation for desktop-size miniaturised assembly systems. The precision of the existing system could be significantly improved by making the manipulator stiffer (i.e. preloaded bearings…) and adjustable to compensate for misalignment. Further improvement could also be made on the calibration of the vision system. The system could be either scaled up or down using the same architecture while adapting the controllers to the scale.Engineering and Physical Sciences Research Council (EPSRC
Investigation into vibration assisted micro milling: theory, modelling and applications
PhD ThesisPrecision micro components are increasingly in demand for various engineering industries,
such as biomedical engineering, MEMS, electro-optics, aerospace and communications. The
proposed requirements of these components are not only in high accuracy, but also in good
surface performance, such as drag reduction, wear resistance and noise reduction, which has
become one of the main bottlenecks in the development of these industries. However,
processing these difficult-to-machine materials efficiently and economically is always a
challenging task, which stimulates the development and subsequent application of vibration
assisted machining (VAM) over the past few decades. Vibration assisted machining employs
additional external energy sources to generate high frequency vibration in the conventional
machining process, changing the machining (cutting) mechanism, thus reducing cutting force
and cutting heat and improving machining quality. The current awareness on VAM technology
is incomplete and effective implementation of the VAM process depends on a wide range of
technical issues, including vibration device design and setup, process parameters optimization
and performance evaluation. In this research, a 2D non-resonant vibration assisted system is
developed and evaluated. Cutting mechanism and relevant applications, such as functional
surface generation and microfluidic chips manufacturing is studies through both experimental
and finite element analysis (FEA) method.
A new two-dimensional piezoelectric actuator driven vibration stage is proposed and
prototyped. A double parallel four-bar linkage structure with double layer flexible hinges is
designed to guide the motion and reduce the displacement coupling effect between the two
directions. The compliance modelling and dynamic analysis are carried out based on the matrix
method and lagrangian principle, and the results are verified by finite element analysis. A
closed loop control system is developed and proposed based on LabVIEW program consisting
of data acquisition (DAQ) devices and capacitive sensors. Machining experiments have been
carried out to evaluate the performance of the vibration stage and the results show a good
agreement with the tool tip trajectory simulation results, which demonstrates the feasibility and
effectiveness of the vibration stage for vibration assisted micro milling.
The textured surface generation mechanism is investigated through both modelling and
experimental methods. A surface generation model based on homogenous matrices
transformation is proposed by considering micro cutter geometry and kinematics of vibration
assisted milling. On this basis, series of simulations are performed to provide insights into the
effects of various vibration parameters (frequency, amplitude and phase difference) on the
generation mechanism of typical textured surfaces in 1D and 2D vibration-assisted micro
milling. Furthermore, the wettability tests are performed on the machined surfaces with various
surface texture topographies. A new contact model, which considers both liquid infiltration
effects and air trapped in the microstructure, is proposed for predicting the wettability of the
fish scales surface texture. The following surface textures are used for T-shaped and Y-shaped
microchannels manufacturing to achieve liquid one-way flow and micro mixer applications,
respectively. The liquid flow experiments have been carried out and the results indicate that
liquid flow can be controlled effectively in the proposed microchannels at proper inlet flow
rates.
Burr formation and tool wear suppression mechanisms are studied by using both finite element
simulation and experiment methods. A finite element model of vibration assisted micro milling
using ABAQUS is developed based on the Johnson-Cook material and damage models. The
tool-workpiece separation conditions are studied by considering the tool tip trajectories. The
machining experiments are carried out on Ti-6Al-4V with coated micro milling tool (fine-grain
tungsten carbides substrate with ZrO2-BaCrO4 (ZB) coating) under different vibration
frequencies (high, medium and low) and cutting states (tool-workpiece separation or nonseparation). The results show that tool wear can be reduced effectively in vibration assisted
micro milling due to different wear suppression mechanisms. The relationship between tool
wear and cutting performance is studied, and the results indicate that besides tool wear
reduction, better surface finish, lower burrs and smaller chips can also be obtained as vibration
assistance is added