Tham khảo tài liệu 'electrical engineering mechanical systems design handbook dorf crc press 2002819s_9', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | F F F b c FIGURE Tensegrities studied in this chapter not to scale a C2T4 bending loads left and compressive loads right b C4T2 and c 3-bar SVD axial loads left and lateral loads right . FIGURE Mass-spring system. However laying out the principles here is an essential first step to discovering those universal properties that do exist. The following example with masses and springs prepares us for two basic principles which we have observed in the tensegrity paradigm. Basic Principle 1 Robustness from Pretension As a parable to illustrate this phenomenon we resort to the simple example of a mass attached to two bungy cords. See Figure . Here KL KR are the spring constants F is an external force pushing right on the mass and tL tR are tensions in the bungy cords when F 0. The bungy cords have the property that when they are shorter than their rest length they become inactive. If we set any positive pretensions tL tR there is a corresponding equilibrium configuration and we shall be concerned with how the shape of this configuration changes as force F is applied. Shape is a peculiar word to use here when we mean position of the mass but it forshadows discussions about very general tensegrity structures. The effect of the stiffness of the structure is seen in Figure . 2002 by CRC Press LLC FIGURE Mass-spring system stiffness profile. There are two key quantities in this graph which we see repeatedly in tensegrity structures. The first is the critical value F1 where the stiffness drops. It is easy to see that F1 equals the value of F at which the right cord goes slack. Thus F1 increases with the pretension in the right cord. The second key parameter in this figure is the size of the jump as measured by the ratio r Stens S. . slack When r 1 the stiffness plot is a straight horizontal line with no discontinuity. Therefore the amount of pretension affects the value of F1 but has no influence on the stiffness. One can also notice that .
