Study on long life large-deflective hinges in molded pantograph mechanisms based on cyclic load-bending fatigue test

Abstract

A molded pantograph mechanism consisted of large-deflective hinges and links is used in a new surface mount system proposed by Mikio Hone. To obtain long life, large-deflective hinges, we showed the method to conduct the repetitive tensile-compressive and bending test on a hinge specimen, and manufactured experimental equipment for a fatigue test. We also evaluated the test equipment and confirmed its effectiveness. The materials of the large-deflective hinge were selected as follows: (1) polypropylene(PP), (2) polymerization blend PP (A1 /spl sim/ A4) which we call PP+R-TPO, that is, the thermoplastic elastomer to which PP monomer and ethylene are polymerized by multistep, (3) machine blend PP (B1 /spl sim/ B3) called PP+EPDM that PP and ethylene propylene-diene monomer (EPDM) were mechanically mixed using a mixer, and (4) another machine blend PP (B1 /spl sim/ B3)(+MAH-PP) that we mixed maleic anhydride modified PP (MAH-PP) with the above (3) machine blend PP. The hinge specimen used for the fatigue test was made with the injection molding machine. From the relationship between the number of cycles leading to the fracture of the hinge and the repetitive tensile-compressive loads in the fatigue test, it has been confirmed that the difference in hinge thickness and the difference in the materials greatly influenced the inner damage of the hinges.