A printing device includes a developer for developing a latent image with toner particles; an imaging plate comprising a plurality of pixel plates; and a plurality of voltage generators connected respectively to the pixel plates. A data collating part collates the data sent from the sending part with a data generated by the first device, and determines that it is abnormal when a mismatch between these data occurs. A clamping sleeve made of elastic material is arranged on the second part of the stem and provided with a slopping element in order to prevent said sleeve from the displacement thereof longitudinally with respect to the stem A protective element provided with a through hole, in which the first part of the stem can be accommodated, is disposed at a distance ranging from 0.