Origami-adapted mechanisms form the basis of an increasing number of engineered systems. As most of these systems require the use of non-paper materials, various methods for accommodating thickness have been developed. These methods have opened new avenues for origami-based design. This work introduces approaches for the design of two new classes of thick-origami systems and demonstrates the approaches in hardware. One type of system, called "conceal-and-reveal,'' is introduced, and a method of designing these mechanisms is developed. Techniques are also developed for designing folding printed circuit boards which are fabricated from a single sheet of material. This enables areas of regional flexibility, leaving other areas stiff. This allows components to be attached to stiff regions and folding to occur at flexible regions. An optimization method is presented to design the geometry of surrogate hinges to aid in monolithic origami-based mechanisms such as flexible PCBs. Examples are shown which demonstrate each of these new techniques.

The (nonlinear) response behavior of a piecewise-linear system is investigated under both deterministic and stochastic excitations in this study. A semi-analytical procedure is developed to predict the system behavior by evaluating the joint probability density functions of the Fokker-Planck equations of the stochastic piecewise-linear system under random excitations via a path-integral solution procedure. From an analysis of the deterministic system, nonlinear system behavior is derived for further analysis of the corresponding stochastic system. The influence of variations in other parameters on the response behavior are also examined. In the stochastic system analysis, which represents a more realistic approach to understanding the system behavior, a Markov process approach is used. By introducing random perturbations in the harmonic excitation, the stochastic responses are examined and compared to those of the corresponding deterministic system. Stability of the various responses including regular and chaotic motions, is investigated by varying the noise intensity. Routes to chaos in period-doubling processes with and without external random perturbations are studied and compared. Stationarity and ergodicity of the chaotic responses of the system are examined via time domain and probability domain simulations. Potential coexisting responses of the piecewise-linear system are examined via the path-integral solutions. It is found that the path-integral solutions can provide global information of the system behavior in the probability domain, and can also verify the potential coexisting responses and discern the relative strength of the coexisting response attractors. / Graduation date: 1996

In humanoid robotics, there is a long pursuit of making bipeds capable of walking in highly unstructured and roughly sensed environments. Within this goal, our objective is to develop a compliant bipedal humanoid robot, based on McKibben pneumatic actuators that can move in these terrains as well as quickly adapt to unpredicted variations on the contact state. We present here the first part of our work, focusing on the design, construction and control of a pneumatic robotic joint capable of achieving the control performance necessary for responding compliantly and accurately to contact transitions while delivering high forces needed to handle the physical challenges associated with rough terrains. In particular, we address our progress in the mechanical and embedded electronic design, actuator modeling, and compliant control strategies for a robotic joint based on fluidic pneumatic artificial muscles (PAMs). The proposed robotic joint has been validated experimentally, exploring various aspects of its performance as well as its shortcomings, but overall demonstrating the potential benefits of using pneumatic muscles. / text

Due to government regulations together with health and safety reasons, there are increasing demands on reducing hazardous polluting chemicals from fossil fuel power plants. Therefore, more efforts are imposed on using renewable resources such as water, wind, solar and tide to produce clean/green electricity. On top of that, there is another increasing demand from Original Equipment Manufacturers (OEMs) to operate power plants with higher load while keep the power loss to the minimum. These requirements drive conventional fluid film bearings to its mechanical and temperature limits. This calls for the development of new bearing system designs. An outstanding tribological performance such as low start-up and break-away friction, excellent resistance to chemical attack and anti-seizure properties, can be achieved by introducing compliant polymer liners. At the same time, bearings with compliant liners may alter rotor-bearing system dynamic behaviour compared to the systems with conventional white metal bearings. The research approach of this thesis is to implement compliant liner on bearing surface, impose synchronous shaft excitation and investigate the effect of bearing design parameters on bearing dynamic response. Plain cylindrical journal bearings with different compliant liner thicknesses were analysed using a FEM approach. The numerical model was compared with an in-house developed code based on the finite difference method (FDM) for a bearing operated at steady state conditions. Results obtained by the numerical models showed good agreement. After verification of the numerical model for fixed geometry journal bearings, models for tilting pad journal bearings were developed. Dynamic behaviour of the tilting pad journal bearing with three pads with line pivot geometry was compared with published data. A good agreement was obtained between the two numerical models. The effect of pad pivot geometry on bearing dynamic response was investigated. Vertical and horizontal shaft configurations were compared in terms of the effect of preload factor, radial clearance, pivot offset, and pad inclination angles. Influence of the elastic properties of compliant liners was also studied. All these factors significantly affect bearing dynamic response. It is shown how these factors should be selected to control the journal orbit sizes. Misalignments in compliant tilting pad journal bearings were analysed for load between pivots and load on pivots with consideration of thermal effects. Significant improvements in bearing performance were obtained with compliant bearings compared to white metal bearings. Furthermore, different polymer materials (PTFE, UHMWPE, pure PEEK and PEEK composite) were characterized using Frequency Response Function (FRF). It was shown that as the excitation frequency increased the equivalent stiffness was more or less constant while equivalent damping decreased exponentially. PTFE had similar equivalent stiffness compared to PEEK. As for equivalent damping, PTFE had slightly higher damping compared to PEEK or UHMWPE. Oil film thickness, oil film temperature and loads on tilting pad journal bearing were measured on 10 MW Kaplan hydroelectric power machine. Test results were compared to FEM model. It was shown that stiffness of the supporting structure may be more important to machine performance than the stiffness of the bearing alone. / <p>QC 20150409</p> / Swedish Hydropower Centre

Compliant mechanisms (CMs) take advantage of the deformation of their flexible members to transfer motion, force, or energy, offering attractive advantages in terms of manufacturing and performance over traditional rigid-body mechanisms (RBMs). This dissertation aims to advance the topology optimization (TO) technique (1) to design CMs that are more effective in performing their functions while being sufficiently strong to resist yield or fatigue failure; and (2) to design CMs from the perspective of mechanisms rather than that of structures, particularly with the insight into the concepts of joints, actuations, and functions of mechanisms. The existing TO frameworks generally result in CMs that are much like load-bearing structures, limiting the applications of CMs. These CMs (1) do not have joints, (2) are actuated by a translational force, and (3) can only do simple work such as amplifying motion or gripping. Three TO frameworks for the synthesis of CMs are proposed in this dissertation and they are summarized below. First, a framework was developed for the design of efficient and strong CMs. The widely used stiffness-flexibility criterion for CM design with TO results in lumped CMs that are intrinsically efficient in transferring motion, force, or energy but are prone to high localized stress and thus weak to resist yield or fatigue failure. Indeed, distributed CMs may have a better stress distribution than lumped CMs but have the weakness of being less efficient in motion, force, or energy transfer than lumped CMs. Based on this observation, the proposed framework rendered the concept of hybrid systems, hybrid CMs in this case. Further, the hybridization was achieved by a proposed super flexure hinge element and a design criterion called input stroke criterion in addition to the traditional stiffness-flexibility criterion. Both theoretical exploration and CM design examples are presented to show the effectiveness of the proposed approach. The proposed framework has two main contributions to the field of CMs: (1) a new design philosophy, i.e., hybrid CMs through TO techniques and (2) a new design criterion—input stroke. Second, a systematic framework was developed for the integrated design of CMs and actuators for the motion generation task. Both rotary actuators and bending actuators were considered. The approach can simultaneously synthesize the optimal structural topology and actuator placement for the desired position, orientation, and shape of the target link in the system while satisfying the constraints such as buckling constraint, yield stress constraint and valid connectivity constraint. A geometrically nonlinear finite element analysis was performed for CMs driven by a bending actuator and CMs driven by a rotary actuator. Novel parameterization schemes were developed to represent the placements of both types of actuators. A new valid connectivity scheme was also developed to check whether a design has valid connectivity among regions of interest based on the concept of directed graphs. Three design examples were constructed and a compliant finger was designed and fabricated. The results demonstrated that the proposed approach is able to simultaneously determine the structure of a CM and the optimal locations of actuators, either a bending actuator or a rotary actuator, to guide a flexible link into desired configurations. Third, the concept of a module view of mechanisms was proposed to represent RBMs and CMs in a general way, particularly using five basic modules: compliant link, rigid link, pin joint, compliant joint, and rigid joint; this concept was further developed for the unified synthesis of the two types of mechanisms, and the synthesis approach was thus coined as module optimization technique—a generalization of TO. Based on the hinge element in the finite element approach developed at TU Delft (Netherlands in early 1970), a beam-hinge model was proposed to describe the connection among modules, which result in a finite element model for both RBMs and CMs. Then, the concept of TO was borrowed to module optimization, particularly to determine the “stay” or “leave” of modules that mesh a design domain. The salient merits with the hinge element include (1) a natural way to describe various types of connections between two elements or modules and (2) a provision of the possibility to specify the rotational input and output motion as a design problem. Several examples were constructed to demonstrate that one may obtain a RBM, or a partially CM, or a fully CM for a given mechanical task using the module optimization approach.

No description available.

This thesis has explored the use of compliant mechanisms in vehicle suspension systems, specifically where a compliant mechanism acts as part of the wheel locating mechanism and as the energy storage element. A compliant mechanism has the potential of reducing part count, joints, and manufacturing and assembly costs of a suspension system. Fatigue failure has been found to be a limiting design constraint which competes with space and weight constraints. Controlling wheel motion in response to control forces has also been shown to be an important functional requirement for a compliant suspension system. Vehicle applications that are best suited for the use of compliant suspension systems are those that are low weight, have low energy storage requirements, and do not require precise vehicle handling characteristics. New compliant suspension concepts have been explored that support the wheel in 3-dimensions to minimize undesired wheel motions. These new concepts demonstrate increased stiffness and decreased stress due to control forces. Of these concepts, the compliant A-Arm proves to be the most promising candidate for future development. It has added advantages of lower space requirements, lower number of extra joints and rigid links, and simpler design for manufacture and assembly. The stiffness, stress, and kinematic characteristics of the compliant A-Arm configuration have been explored. This configuration has a non-linear force-deflection curve that is facilitated by the stress-stiffening effects of large deflections. A closed-form linear stiffness solution and a pseudo-rigid-body model has also been developed to aid in the initial design of the compliant A-Arm in a suspension system.

This thesis presents research on the feasibility of applying compliant-ortho-planar springs (COPS) to rotational applications. The primary motivation of this research is the application of COPS to a continuously variable transmission (CVT). The design space limitations, loading conditions, stresses, stress concentrations, and limitations of current design tools, such as pseudo-rigid-body models (PRBM) for COPS, are discussed. A new 3D PRBM is presented along with a discussion on the possible applications of such to a rotating COPS. Stress stiffening and lateral stability are two major phenomena occurring in a rotating COPS. Both phenomena are a direct result of the inertial loads a COPS would be subjected to in a rotational environment. The results show how stress stiffening and lateral buckling in the legs are influenced by design parameters. Conclusions and recommendations for further research are recommended.

The objective of this research is to present a new model for predicting the piezoresistive effect in microflexures experiencing bending stresses. A linear model describing piezoresistivity exists for members in pure tension and compression. Extensions of this model to more complex loading conditions do not match experimental results. An accurate model of piezoresistivity in complex loading conditions would expand the design possibilities of piezoresistive devices. A new model to predict piezoresistive effects in tension, compression, and more complex loading conditions is proposed. The focus of this research is to verify a unidirectional form of this proposed model for microflexures in tension and bending. Implementation of the unidirectional form of the model involves geometric design, stress analysis, and electrical analysis. One of the ways to implement the model is with finite-element analysis (FEA). The piezoresistive FEA for flexures (PFF) algorithm is an FEA implementation of the unidirectional form of the model for flexures. A case study is then given in which the resistance curves of two test devices are predicted with the PFF algorithm. Results from the PFF implementation of the unidirectional form of the model show a close comparison between analytical prediction and experimental results. This new model could contribute to optimized sensors, feedback control of microdevices, nanopositioning, and self-sensing microdevices.

<p>Minimally Invasive Robotic Surgery (MIRS) has revolutionized the way modern surgery is conducted by allowing for smaller incisions, finer control, reduced pain, and faster recovery. The state-of-the-art end-effector technology used for MIRS are tools based off of the rigid-body instruments used in traditional ‘open’ surgery. The rigid nature of the end-effectors, specifically the grasping jaws, leads to a lack of force feedback when implemented in a robotic system. </p> <p>Without additional feedback from active sensing, the blanching that occurs from restricted blood flow around a grasping site is the only indication a surgeon can use to assess the force applied to a tissue. Ongoing efforts to develop active force sensing solutions are currently faced with two major obstacles: miniaturization and sterilization. The lack of force feedback causes a gap between intention and result during robotic surgery. </p> <p>This work proposes the introduction of Visual Force Feedback (VFF) through the integration of a compliant end-effector design. Visual Force Feedback is an intuition, developed through practice, that allows a surgeon to estimate the reaction force of a compliant mechanism by the deflection of the outer flexures. An understanding of the relationship between opening size, flexure deformation, and pinch force allows for rapid estimation of the force applied to a manipulated object. </p> <p>Force and dimensional data were gathered through finite element simulation and the finite element model was validated with physical experimentation on a custom test bench. Multiple functions relating the flexure deformation to the reactionary force, referred to as pinch force, for specific opening sizes were resolved. Notable observations made through the analysis of these results were: (1) a closely linear relationship between outer flexure deformation and pinch force in both experimental and computational results and (2) a higher rate of pinch force increase due to draw displacement as an effect of wider jaw opening. These findings are intended to help shrink the gap between intention and result in the field of MIRS.</p>