Process for the detection of superimposed sheets, apparatus for performing the process and application to bank notes

Claim 1

A process for the detection of superimposed sheets by evaluating their surface mass, comprising the steps of: passing sheets oriented in a given direction on a transporting system between a particle source and a particle detector, counting the number of particles received by the detector by measuring the frequency F g of the pulses of the detector in order to determine the surface mass, and eliminating the sheets with a high superimposition level by comparing the count frequency with a limit value.

Claim 8

An apparatus for the detection of superimposed sheets, comprising: a beta particle source and a Geiger-Muller counter arranged on opposite sides of a sheet transportation path, the Geiger counter having a supply circuit, the sheets being oriented in a given direction, an adding counter validated by the pulses from the Geiger counter, the pulses having a frequency which is a function of the surface mass of the sheets and the adding counter being controlled by an oscillator supplying a signal of frequency F o , an overflow output of the counter supplying a signal which is a function of the signal from the oscillator and pulses from the Geiger counter indicating, in the case of an overflow, a high level of superimposition of the sheets, a coding wheel associated with the device for transporting the sheets along the path, the pulses of the coding wheel decrementing a subtract counter preloaded to a mean value representative of a normal sheet width, a circuit for detecting the presence of a sheet and a logic circuit taking account of the output signals from the sheet presence detection circuit, the adding counter and the subtract counter for controlling the elimination of the sheets by a motor element of a switching means located in the transportation path downstream of the beta source and the Geiger counter with respect to the direction that the sheets are being transported.

Claim 9

An apparatus for the detection of superimposed sheets, comprising: a beta particle source and a Geiger-Muller counter arranged on opposite sides of a sheet transportation path, the Geiger counter having a supply circuit, the sheets being oriented in a given direction, an adding counter validated by the pulses from the Geiger counter, the pulses having a frequency which is a function of the surface mass of the sheets and the adding counter being controlled by an oscillator supplying a signal of frequency F o , an overflow output of the counter supplying a signal which is a function of the signal from the oscillator and pulses from the Geiger counter indicating, in the case of an overflow, a high level of superimposition of the sheets, a coding wheel associated with the device for transporting the sheets along the path, the pulses of the coding wheel decrementing a subtract counter preloaded to a mean value representative of a normal sheet width, a circuit for detecting the presence of a sheet and a logic circuit taking account of the output signals from the sheet presence detection circuit, the adding counter and the subtract counter for controlling the elimination of the sheets by a motor element of a switching means located in the transportation path downstream of the beta source and the Geiger counter with respect to the direction that the sheets are being transported.