US 4,258,326 AGranted

Capacitive detection of absent and/or double sheets in the sheet transport path of a printing machine

AssigneeVEB Polygraph Leipzig Kombinat fur Polygraphische Maschinen und Ausrustungen

InventorAlbrecht Johne

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Abstract

A detecting capacitive structure undergoes changes in capacitance value depending upon whether it is detecting, in the sheet transport path of a printing machine, a normal or single sheet, an absent sheet, or a double or stuck-together sheet, so that corrective action can be initiated, such as the skipping of a printing cycle. The detecting capacitive structure and also a reference capacitive structure constitute the capacitances of two RC circuit stages to which an input signal is applied and then removed. The variations with respect to time of the output signals from the two RC circuit stages are then compared, both during application of the input signal and subsequent to removal of the input signal. This comparison of time responses of the two RC circuit stages serves as the basis of the detection. The effect of the normal, absent or double sheet upon capacitance value is detected by monitoring a response dependent upon the time-constants of the RC circuit stages, without the detecting capacitive structure forming the capacitor of or resonant circuit.

Claims12

Dependent claims

In a detecting system of the type operative for detecting absent and/or multiple sheets in the sheet transport path of a printing machine and including a first RC circuit stage and a second RC circuit stage, a combination comprising a detecting capacitive structure forming the capacitance of the first RC circuit stage and operative for capacitively sensing normal, absent and multiple sheets;

a reference capacitive structure forming the capacitance of the second RC circuit stage;
means for applying an electrical signal to said detecting capacitive structure and to said reference capacitive structure, said applying means including means operative for applying a voltage pulse to the inputs of the first RC circuit stage and the second RC circuit stage;
and comparator circuit means connected to said detecting capacitive structure and said reference capacitive structure, said comparator circuit means including means operative for comparing the response with respect to time exhibited by both RC circuit stages in response to application of said pulse and also the response with respect to time exhibited by the first RC circuit stage and the second RC circuit stage subsequent to termination of the pulse whereby a signal is generated, which signal indicates whether a normal or an absent or multiple sheet is being detected.

Dependencies are inferred from the claim text.