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

US4258326A · kind A · utility

Assignee

• VEB Polygraph Leipzig, Kombinat fur Polygraphische Maschinen und Ausrustungen · DE

Inventor

• Albrecht Johne · Dresden, DE

Key dates

• Filing date: Apr 4, 1979
• Grant date: Mar 24, 1981
• Expiry date: Apr 4, 1999

Classification

• Technology area (CPC B): Performing Operations; Transporting
• CPC primary: B65H2553/23
• WIPO field: Handling
• WIPO sector: Mechanical engineering

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.