Bounce and Chaotic Motion in Impact Print Hammers

The basis of this paper is a lumped-parameter description of an impact printer actuator of the stored-energy type. All constants necessary to describe the actuator and the ribbon/paper pack are derived from measurements. The equations of motion are integrated both for single- and multiple-current pulse excitation. The numerical results show that for low repetition rates, each impact is distinct and independent, but at higher rates the impacts interact. The interaction manifests itself initially as flight-time and print-force variations: Strict periodicity of the actuator motion is lost, as shown in Poincaré plots for the actuator motion, and randomness sets in. At extremely high repetition rates, the actuator “hangs up” and the backstop no longer participates in the actuator dynamics. During settle-out the actuator motion is extremely sensitive to the timing of the current excitation. This fact can, in principle, be exploited to achieve extremely fast cycle times. However, without knowledge of the state of the actuator, as is commonly the case, this sensitivity is detrimental to print quality.