This invention relates to a printing unit which includes an inking assembly, particularly a printing unit which has, as its printing member, a rotary stamp for cancelling mail.
The inking of a printing member, such as a rotary stamp, is conventionally effected by transferring ink from a felt roller being in tangential contact with the printing member. Printing units having a simple inking member of this type have several disadvantages. Thus, the quality of ink print is often objectionable. The reason therefor resides in the fact that the felt roller is either non-driven or can be driven only at low rpm's otherwise the large centrifugal forces would expel ink from the felt material. Since, however, the rotary stamp is driven with an rpm of approximately 1400, there results a velocity difference between the stamp and the inking roller which, in turn, causes a removal (shaving off) of ink-loaded felt particles by the stamp, resulting in a smearing of the imprint. Further, because of the limited ink absorbing capacity of the felt layer, the felt roller has to be frequently inked. Further, a printing unit equipped with an inking assembly of this type provides gradually fading imprints until the periodic re-inking of the felt roller is effected. It is a further disadvantage that in case the felt roller has a vertically oriented axis, the ink wanders downwardly by gravity, resulting in a non-uniform inking of the rotary stamp.