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

Automatic Microassembly of Tissue Engineering Scaffold

Ph.DDOCTOR OF PHILOSOPH

Modellbasierte Entwicklung von Methoden Algorithmen und Werkzeugen zur Analyse und Synthese nachgiebiger Mechanismen

Nachgiebige Mechanismen (NM) sind in technischen Anwendungen aufgrund ihrer Vorteile weit verbreitet. Die Berechnung des Verformungsverhaltens unter dem Einfluss äußerer Belastungen stellt aufgrund von geometrischer Nichtlinearität eine anspruchsvolle Aufgabe dar. Mit Hilfe der in dieser Arbeit beschriebenen Modellgleichungen auf Basis der nichtlinearen Balkentheorie können ebene und räumliche NM sekundenschnell numerisch berechnet werden. Dazu werden über reine Biegung hinaus, Querkraftschub und Querkontraktion im Modell berücksichtigt und Empfehlungen für die zu verwendende Theorie abgeleitet. Zudem werden Algorithmen zur Dimensionierung von NM gegeben, mit Hilfe derer die Verformungseigenschaften im Hinblick auf konkrete Zielkriterien verbessert werden können. Abschließend werden die Methoden in drei eigenständig ausführbare und frei zugängliche Softwarewerkzeuge implementiert. Durch deren Entwicklung wird ein Beitrag zum Entwurf sowie zur Analyse und Synthese von NM geleistet.Compliant mechanisms are widely used in technical applications, especially in robotics, precision engineering, measurement and medical technology. Their deformation behavior is significantly influenced by the design of selected compliant sections, for example by systematically reducing cross-sectional dimensions. Movement of the mechanism is predominantly achieved by bending these sections. Due to geometric nonlinearity, calculating the deformation behavior under the influence of external loads is a challenging task in analyzing and synthesizing compliant mechanisms. Therefore, this work contributes to the analytical modelling and, consequently, to the analysis and synthesis process. A set of model equations is given for plane and spatial use cases. They can be used to characterize compliant mechanisms with varying cross sections, curvatures, materials, and branching points. Since we are considering arbitrary mechanisms, the equations are given in a recursive form. Due to structures of varying cross sections, shear and lateral contraction are also considered in the model in addition to pure bending. Investigations are carried out to define when to consider which effects, depending on the geometry. Based on these investigations, recommendations are given for the theory to be used. By formulating the equations in a unified form, it is possible to customize the theory for individual sections of a compliant mechanism. Furthermore, the model is validated by example mechanisms for two- and three-dimensional application cases using the finite element method and experimental investigations. Thereby, the recommendations for the suitable theory are included. Subsequently, algorithms for dimensioning individual flexure hinges and compliant mechanisms are given. This allows for improved motion behavior with respect to specific objectives. Finally, the methods are implemented in three stand-alone executable software tools that are freely available. Through their development, a contribution is made to the design as well as the analysis and synthesis of flexure hinges and compliant mechanisms