Analytical Models and Impact Force of Print Hammers

Abstract

This paper presents a method of designing the print hammer or the wire driving lever of an impact printer. A beam with a mass at the free end and a rigid body around the pivot point is considered to be the essential structure of a print hammer, and the relationship of this funda-mental structure to the impact force is studied. The driving point mechanical immittances are derived from this infinite degrees of freedom model taking account of the boundary conditions ; these equations are expanded to infinite series by use of Mittag-Leffler's theorem. One of the ordinary methods of designing an acoustic apparatus is to use the equivalent circuit. But in the case presented here, it is more convenient to use the equivalent mechanism which is expressed in terms of simple vibrating systems. To describe such mechanism, two types of simple massspring systems, those with resonant and anti-resonant vibrating elements, and additional mechanisms are considered. These expressions enable us to obtain the approximate impact force more easily than by other methods. Impact forces calculated by use of these expressions and while neglecting higher order vibrations show good correlation with those measured experimentally.