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2870 |
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Synthesis of Multi-axis Serial Flexure Systems |
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Design of Precision Machines and Instruments |
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In this paper we show how to design any serial precision flexure system so that one obtains the best design for a given set of performance characteristics—kinematics, range, stiffness, load capacity, and thermal stability. Serial flexure systems consist of many flexure elements chained together in series. In Fig. 1 a serial flexure system is contrasted with a parallel flexure system. Serial flexure systems (a) are more easily designed to exhibit many degrees of freedom (DOFs), (b) exhibit larger ranges of motion in a more compact space, and (c) enable cancelation of parasitic errors. The problem with serial flexure systems is that even experienced designers sometimes have difficulty visualizing motions that occur when various types of flexure elements are connected in series. Designers currently rely on motion visualization and pattern recognition skills for synthesizing serial flexure systems. In this paper we will demonstrate a combination of qualitative design rules and quantitative models that may be used to rapidly design serial flexure systems that yield the exact performance one desires.
More specifically, the contributions of this paper are:
1. This method enables one to consider how to combine flexure building blocks in series to achieve any desired DOFs. We have created a comprehensive library of geometric shapes that link serial flexure designs to desired motions [1]. These “graphical” representations of flexure performance enable one to understand what a flexure should look like if one wishes to achieve certain motion characteristics. After selecting the right design via these shapes, we show how to use screw theory to tune and optimize a concept for specific design requires.
2. This method helps designers ascertain when it is best to use a serial or a parallel flexure system for a given application. In some instances a parallel flexure system may satisfy all the design requirements with less complexity, lower cost, and better dynamic, and elastomechanic behavior than a serial flexure system. Identifying when to design a serial or parallel flexure system is not a trivial task.
3. With this new approach, we have found new design rules for serial flexure systems. These rules enable designers to rapidly identify concepts that possess desired symmetry, load capacity, and constraint redundancy. They may also be used to optimize the layout of a flexure system so that one can achieve the best flexure system’s stiffness and dynamic characteristics.
These principles will be demonstrated via the design of a Cartesian flexure stage for micro and nano-positioning. This case study will walk through the steps of the method, show how they are applied, and demonstrate how our new graphical approach and design rules are used. The output from the quantitative elements of our approach will be compared with experimental data.
[1] Hopkins J.B., Design of Parallel Flexure Systems via Freedom and Constraint Topologies (FACT), Masters Thesis, Massachusetts Institute of Technology, 2007. |
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