Conclusiones

This chapter presents novel and innovative research exemplifying the opportunities created by new and economical manufacturing technologies in the design and fabrication of modern machine tools with case examples in the area of flexure-based mechanism. Simplicity, accuracy, and repeatability make flexure-based mechanisms a natural technology for the construction of mesoscale systems for single-use/reduced-life, precision motion applications, and the robotics and medical industry. Therefore, a new flexural joint was demonstrated with the combination of

Figure 46. Delta LMMT experimental work.

(a) Reference image of end-effector, (b) selected kernel, (c) reference (in markers) and commanded circular trajectory and (d) cross-correlation algorithm along the horizontal direction of (a).

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traditional and additive manufacturing processes. The hybrid joint is the result of breaking the geometry of a conventional flexure into a host and an insert. The insert provides the relative motion of the host by means of deflection while the host provides structural stiffness and a means of connecting the joint to the mechanism structure. This overcomes complexities of manufacturing a monolithic mechanism.

A simplified-2D finite element model was developed to study the mechanics of the flexure and to produce design rules that alleviate the effects of low accuracy and poor surface finishing, anisotropy, reductions in material properties of components, and small holding forces. Preliminary structural analysis revealed two main mechanisms of stress concentration in the hybrid flexure.

Namely, the localized contact stresses at the interface between the host and the insert and the notch tip stresses. Further parametric analysis on this model was used to track the stress in the components, the contact pressure at the interface and the strain energy distribution for different penetration depths. These computational experiments resulted in a general, dimensionless, relation to compute the optimal penetration depth (insertion distance where the elastic work done by the host material is minimum relative to that one done by the flexure) for different selections of joint materials and flexural thickness. For example, in the case of an aluminum host and steel inserts, the optimum penetration distance is six times greater the thickness of the insert whereas in the case of an ABS structure and steel inserts, the optimum penetration desistance is ten times greater than the insert thickness. Studying the effect of pre-stressing the interface resulted in a systematic approach to calculate the required amount of interference for a required rotation of the joint while avoiding delamination. Simulations show that delamination might take place when the intensity of the flexing stress field is below five times the intensity of the preload stress field. Finally, this section proposes the development of failure criteria for flexural pivots based on fracture mechanics. This idea is based on the shown similarity between the stress fields near the tip of the interface and the Irwin stresses for fracture. Such a model can be used to experimentally identify values limiting values of KI for different set of materials and dimensions of the interface. This result conclude the set of analytic tools and design rules for hybrid flexures.

Design-for-fabrication strategies with multilayered composites and hybrid flexures were demonstrated in the construction of mesoscale devices and machine components with case examples in the areas of precision engineering, medical training and machine tools for reduced life

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applications. A piezo-electric actuated 4-bar mechanism was built with hybrid-flexures. Open loop bandwidths of 50 Hz and closed-control tracking errors below 50 nm at speeds of 150 µm/s demonstrated that hybrid-flexures are fit for use in applications as stringent as nanopositioning.

The design and manufacture of a flexure-based XYZ sensor demonstrated the use of hybrid-flexures in the medical applications of knot -tying and suturing training. This solution demonstrated the potential of hybrid-flexures in the construction of devices that quantify the magnitude of the forces as well as provide information on the quality of the motion generated.

Finally, this chapter presented the design and fabrication of a miniature Delta robot as example of a manufacturing technique to produce mesoscale electromechanical systems via lamination. The structure of the robot is adapted to be flexure-based where the flexures are design to take advantage of the lamination schemes. With the help of the presented stiffness analysis, we were able to characterize the overall stiffness of the mechanism. This was use to arrive to an optimal pop-up angle and estimate the size of the workspace, given the characteristics of the chosen drives. This example presents solutions to the integration of common components in mechanical systems such as limit switches, linear guides and actuation elements. The simplicity of the manufacturing techniques in this process makes it easy to exploit the broad spectrum of open source hardware and software tools available for the construction and communication with the devices. After the mechanism assembly, we demonstrated its functionality with the implementation on an open-loop controller. The precision of these devices could benefit from the implementation of closed-loop control algorithms.

The cases of study here where shown to perform successfully. They represent a repertory of creative solutions applicable to the design of devices with hybrid flexures and can find applications in the fields of medical industry, soft robotics, flexible electronics, machine design-iteration and elimination of errors.

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CHAPTER 5: OPPORTUNITIES CREATED BY PERVASIVE