Hybrid Power Management for Office Equipment

Office machines (such as printers, scanners, fax, and copiers) can consume significant amounts of power. Few studies have been devoted to power managemen

Active Metastructures for Light-Weight Vibration Suppression

The primary objective of this work is to examine the effectiveness of metastructures for vibration suppression from a weight standpoint. Metastructures, a metamaterial inspired concept, are structures with distributed vibration absorbers. In automotive and aerospace industries, it is critical to have low levels of vibrations while also using lightweight materials. Previous work has shown that metastructures are effective at mitigating vibrations but does not consider the effects of mass. This work considers mass by comparing a metastructure to a baseline structure of equal mass with no absorbers. The metastructures are characterized by the number of vibration absorbers, the mass ratio, and the natural frequencies of the vibration absorbers. The metastructure and baseline structure are modeled using a lumped mass model and a distributed mass model. The lumped mass model allows for mass and stiffness parameters to be varied independently without the need to consider geometry constraints. The distributed mass model is a more realistic representation of a physical structure and uses relevant material properties. The steady-state and transient time responses of the structure are obtained. The results of these models examine how the performance of the structure varies with respect to the number of vibration absorbers and the mass ratio. Additionally, the stiffness and mass distributions of the vibration absorbers are considered. When the ratio of stiffness over mass varies linearly, the absorbers create broad-band suppression. Overall, these results show it is possible to obtain a favorable vibration response without adding additional mass to the structure. The distributed vibration absorbers are realized through geometry modifications on the centimeter scale. To obtain the complex geometry needed for these structures, the metastructures are typically manufactured using 3D printers, specifically the Objet Connex 3D printer. To better understand the damping properties of the materials used by the Objet Connex, the viscoelastic properties are characterized. These properties are characterized by measuring the frequency and temperature dependent complex modulus values using a dynamic mechanical analysis (DMA) machine. The material properties are incorporated into the Golla-Hughes-McTavish (GHM) model to capture the damping effect. Using the time-temperature equivalence, the material properties are transformed to various temperatures, allowing the response of the structures to be modeled at various temperatures. A 3D printed metastructure is experimentally tested and compared to the GHM model. These results show the GHM model can accurately predict the natural frequencies of the vibration absorbers. Lastly, the concept of adding active vibration control to a metastructure to get additional vibration suppression is explored. This is done by attaching piezoelectric materials to the metastructure and utilizing the positive position feedback (PPF) control law to further reduce vibrations. Two active vibration absorber designs are explored; the first uses a stack actuator to control the position of a single absorber and the second design bonds PZT patches in a bimorph cantilevered configuration to the beam of one absorber. This work shows that the active vibration absorber design utilizing a stack actuator is not practical, but the PZT bimorph configuration is capable of further reducing vibrations. Due to the metastructure design, each mode corresponds to the oscillation of a single absorber. When a single vibration absorber is active, the controller can control the corresponding mode. Overall, this shows that integrating active vibration control into a metastructure design can provide additional performance improvements.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144044/1/reichl_1.pd

Fibre-reinforced additive manufacturing: from design guidelines to advanced lattice structures

In pursuit of achieving ultimate lightweight designs with additive manufacturing (AM), engineers across industries are increasingly gravitating towards composites and architected cellular solids; more precisely, fibre-reinforced polymers and functionally graded lattices (FGLs). Control over material anisotropy and the cell topology in design for AM (DfAM) offer immense scope for customising a part’s properties and for the efficient use of material. This research expands the knowledge on the design with fibre-reinforced AM (FRAM) and the elastic-plastic performance of FGLs. Novel toolpath strategies, design guidelines and assessment criteria for FRAM were developed. For this purpose, an open-source solution was proposed, successfully overcoming the limitations of commercial printers. The effect of infill patterns on structural performance, economy, and manufacturability was examined. It was demonstrated how print paths informed by stress trajectories and key geometric features can outperform conventional patterns, laying the groundwork for more sophisticated process planning. A compilation of the first comprehensive database on fibre-reinforced FGLs provided insights into the effect of grading on the elastic performance and energy absorption capability, subject to strut-and surface-based lattices, build direction and fibre volume fraction. It was elucidated how grading the unit cell density within a lattice offers the possibility of tailoring the stiffness and achieving higher energy absorption than ungraded lattices. Vice versa, grading the unit cell size of lattices yielded no effect on the performance and is thus exclusively governed by the density. These findings help exploit the lightweight potential of FGLs through better informed DfAM. A new and efficient methodology for predicting the elastic-plastic characteristics of FGLs under large strain deformation, assuming homogenised material properties, was presented. A phenomenological constitutive model that was calibrated based upon interpolated material data of uniform density lattices facilitated a computationally inexpensive simulation approach and thus helps streamline the design workflow with architected lattices.Open Acces

Design, Analysis and Experimental Evaluation of 3D Printed Variable Stiffness Structures

The rapid progress of additive manufacturing (AM) introduces new opportunities but also new challenges for design and optimization to ensure manufacturability, testability and accurate representation/prediction of the models. The present dissertation builds a bridge between design, optimization, AM, testing and simulation of advanced optimized variable-stiffness structures. The first part offers an insight on the mechanical, viscoelastic and failure characteristics of AM continuous fiber composites. This understanding was used in the second part to investigate the feasibility of different topology and fiber-orientation optimization methods and the manufacturability of the resulting models. The study also assesses the effects of the manufacturing constraints on the stiffness. In the third part, a framework was used to optimize the topology and orientation of lattice structures subjected to stress constraints. This framework uses homogenized stiffness and strength to expedite the optimization, and Hill’s criterion to express the stress constraint. Those properties are implemented in the macrostructure topology optimization to improve the lattice structure stiffness. The optimized design is projected and post-treated to ensure manufacturability. The framework tested for two case studies producing designs with enhanced yield strength. The last part of this research challenges the capabilities of AM to fabricate, for the first time, an optimized flexible wing model with internal structures. The wing was tested in a low-speed wind tunnel to validate a robust computational model which enables the future study of the aeroelastic performance of different optimized wing models. This dissertation demonstrates that the conjoint use of topology and orientation optimization and AM results in advanced lighter structures with enhanced stiffness and/or strength

A New framework for an electrophotographic printer model

Digital halftoning is a printing technology that creates the illusion of continuous tone images for printing devices such as electrophotographic printers that can only produce a limited number of tone levels. Digital halftoning works because the human visual system has limited spatial resolution which blurs the printed dots of the halftone image, creating the gray sensation of a continuous tone image. Because the printing process is imperfect it introduces distortions to the halftone image. The quality of the printed image depends, among other factors, on the complex interactions between the halftone image, the printer characteristics, the colorant, and the printing substrate. Printer models are used to assist in the development of new types of halftone algorithms that are designed to withstand the effects of printer distortions. For example, model-based halftone algorithms optimize the halftone image through an iterative process that integrates a printer model within the algorithm. The two main goals of a printer model are to provide accurate estimates of the tone and of the spatial characteristics of the printed halftone pattern. Various classes of printer models, from simple tone calibrations, to complex mechanistic models, have been reported in the literature. Existing models have one or more of the following limiting factors: they only predict tone reproduction, they depend on the halftone pattern, they require complex calibrations or complex calculations, they are printer specific, they reproduce unrealistic dot structures, and they are unable to adapt responses to new data. The two research objectives of this dissertation are (1) to introduce a new framework for printer modeling and (2) to demonstrate the feasibility of such a framework in building an electrophotographic printer model. The proposed framework introduces the concept of modeling a printer as a texture transformation machine. The basic premise is that modeling the texture differences between the output printed images and the input images encompasses all printing distortions. The feasibility of the framework was tested with a case study modeling a monotone electrophotographic printer. The printer model was implemented as a bank of feed-forward neural networks, each one specialized in modeling a group of textural features of the printed halftone pattern. The textural features were obtained using a parametric representation of texture developed from a multiresolution decomposition proposed by other researchers. The textural properties of halftone patterns were analyzed and the key texture parameters to be modeled by the bank were identified. Guidelines for the multiresolution texture decomposition and the model operational parameters and operational limits were established. A method for the selection of training sets based on the morphological properties of the halftone patterns was also developed. The model is fast and has the capability to continue to learn with additional training. The model can be easily implemented because it only requires a calibrated scanner. The model was tested with halftone patterns representing a range of spatial characteristics found in halftoning. Results show that the model provides accurate predictions for the tone and the spatial characteristics when modeling halftone patterns individually and it provides close approximations when modeling multiple halftone patterns simultaneously. The success of the model justifies continued research of this new printer model framework

Appearance-based image splitting for HDR display systems

High dynamic range displays that incorporate two optically-coupled image planes have recently been developed. This dual image plane design requires that a given HDR input image be split into two complementary standard dynamic range components that drive the coupled systems, therefore there existing image splitting issue. In this research, two types of HDR display systems (hardcopy and softcopy HDR display) are constructed to facilitate the study of HDR image splitting algorithm for building HDR displays. A new HDR image splitting algorithm which incorporates iCAM06 image appearance model is proposed, seeking to create displayed HDR images that can provide better image quality. The new algorithm has potential to improve image details perception, colorfulness and better gamut utilization. Finally, the performance of the new iCAM06-based HDR image splitting algorithm is evaluated and compared with widely spread luminance square root algorithm through psychophysical studies