design and fabrication of multimaterial flexible mechanisms with ...

47and risk elimination of flexible component damage. It also helps overcome problemsof undesired material infiltration concern and weak bonding between the flexible componentand one of the part materials. These effects are very similar to those of preencapsulation.However, unlike pre-encapsulation, this process requires the flexiblecomponent to capable of being fixtured. When fixturing is not possible, one may simplyresort to the combination of pre-encapsulation and one of the four cross-boundaryembedding methods or else apply pseudo-boundary formation for embedding the preencapsulatedcomponent.The approach is illustrated in Figure 3.17, and it follows the same sequence asused to create the fabric-reinforced hinge in Figure 3.11. The fabric is encased entirelyin soft material, including where it is nominally surrounded by hard material.This approach also helps to avoid failure of the flexible member at the original hardmaterial/soft material interface because the soft material helps to distribute loads.Functionally, the modified design in Figure 3.17 is very similar to the original specificationin Figure 3.1. The stiffness of the hard material region is not seriouslycompromised if the thin inclusion of soft material is hydrostatically incompressible(e.g. silicone rubber or polyurethane with a Poisson’s ratio of 0.5) because it cannotbulge or contract laterally, being restrained by the hard material above and below.Why choose these alternative methods?The two alternative methods of embedding flexible components offer advantages anddisadvantages as indicated in table 3.2. Pseudo-boundary formation is easier andsafer than real cross-boundary embedding. It also reduces stress concentration on theflexible insert and helps overcome infiltration and bonding issues as previously mentioned.Hence, this process is the most favorable as long as the potential reduction inanchoring strength is acceptable. Pre-encapsulation, on the other hand, is a preparatoryprocess which adds extra labor prior to performing one of the four methods ofcross-boundary embedding. Therefore, you would generally want to avoid this processif it is not required. Most of the benefits of pre-encapsulation can also be gainedby pseudo-boundary formation except for the preparation of flexible components thatcannot be fixtured. Hence, in essence, pre-encapsulation is to be employed only when