Holographic Interferometry Deformation Study of a Printer Type-piece

Holographic interferometry with a pulsed ruby laser is used to determine printer type-piece deformation caused by impact of the print hammer. A variety of type-piece designs are examined. Effects of impact velocity and hammer-type-piece alignments are studied. Means of obtaining stress information from the holographic data are considered. Cubic spline methods are used to smooth the holographic data and to obtain continuous first and second derivatives. The stresses calculated from the holographic data agree well with those obtained by other means such as finite element analysis. Some limitations of the holographic technique as well as its advantages are discussed. Considerable type-piece twisting is observed; this was not expected or known previously. The most significant result is that a type-piece tends to twist when impacted by the hammer at any point other than the exact center. The twist angle is of the same magnitude as the angle of out-of-plane motion of the type. Hence the type may impact the platen on one corner or side edge. Also, the type bends greatly in the necked down region adjacent to the character and does not pivot by a large amount at its bearing point. Twisting motion is propagated from one end of the type to the other.