Device for verifying if thermal printer is operating correctly

摘要

A method and apparatus is described for checking the operation of a thermal dot printer during a printing cycle. When a pattern is to be printed a count of the number of printing elements intended to be operated in the cycle is stored. A signal indicative of the total current drawn from a supply by the operated printing elements is compared with the stored count. If the comparison indicates that all or a sufficient number of elements have been operated to effect printing, operation of the printing elements in further printing cycles is permitted otherwise further printing is inhibited. In an alternative method the printing elements are operated to print data in machine readable form and the data is read to produce a signal which is compared with data intended to be printed. The printing elements may print the data in a form for visual inspection and in machine readable form. The printer may form part of a franking machine in which the printed data is a franking of a mail item.