Double document detection system having dectector calibration

Claim 1

In a double document detection system, wherein documents are successively advanced along a document feed path located between a light emitter and a corresponding light detector for generating an output signal, and wherein means are provided responsive to the output signal to detect the double document condition, the improved method of calibrating the system comprising the steps of providing a calibration document in the document feed path, generating a series of increasingly wider pulses, generating a series of drive pulses corresponding to the increasingly wider pulses for driving the light emitter at a required energy level, monitoring the output signal of the light detector until the output signal reaches a predetermined value, and fixing the width of one of the pulses in the series of increasingly wider pulses corresponding to the output signal of the predetermined value.

Claim 40

A method for double-feed document detection in a document handling machine, wherein documents are successively advanced along a document feed path between a light emitter and a corresponding light detector, wherein the light emitter generates light of an energy level penetrating at least one document in the document feed path and causing an output signal of the light detector, wherein the output signal changes its value in respect to the opacity of at least one document in the document feed path, wherein the value of the output signal is analyzed to detect if there is more than one document in the document feed path, the method including a calibration cycle and a subsequent operation cycle, wherein the light emitter is protected from damage by excessive power dissipation, wherein the calibration cycle comprises the steps of: providing a single calibration document in the document feed path, generating a series of increasingly wider pulses, transforming said series of increasingly wider pulses into a series of respective ramp pulses of increasing height, generating a series of drive pulses corresponding to the increasingly higher ramp pulses for driving the light emitter, monitoring the respective output signal's value until it reaches a predetermined value, fixing the width of one of the increasingly wider pulses corresponding to said predetermined value, storing the pulse of the fixed width for restoring the fixed width of the pulse in the situation of power outage immediately after the power up, and removing the calibration document from the document feed path; and wherein the operation cycle comprising the steps of: generating pulses of the fixed width determined in the calibration cycle, transforming the pulses of determined width in the calibration cycle into ramp pulses, each ramp pulse having a peak time, generating drive pulses corresponding to said ramp pulses, wherein each ramp pulse starts from the same voltage level, wherein said drive pulses are not generated until the peak time of the respective ramp pulse; and monitoring the output signal corresponding to at least one document in the document feed path, comparing the output signal with a required value, indicating a double-feed document condition if the monitored output signal exceeds the required value, counting a prolongation of the detected double-feed document condition, detecting a "true" double if the prolongation of the double-feed document condition exceeds the predetermined value, double-feed document condition including a first and a second overlapped documents, measuring a distance between a front edge of the first overlapped document and a rear edge of the second overlapped document, and detecting a double-feed document condition if said distance exceeds a predetermined distance, wherein the predetermined distance may be set up for various document sizes and speeds of the documents motion.

Claim 41

A method for double-feed document detection in a document handling machine, wherein documents are successively advanced along a document feed path between a light emitter and a corresponding light detector, wherein the light emitter generates light of an energy level penetrating at least one document in the document feed path and causing an output signal of the light detector, wherein the output signal changes its value in respect to the opacity of at least one document in the document feed path, wherein the value of the output signal is analyzed to detect if there is more than one document in the document feed path, the method including a calibration cycle and a subsequent operation cycle, wherein the light emitter is protected from damage by excessive power dissipation, wherein the calibration cycle comprises the steps of: providing a single calibration document in the document feed path, generating a series of increasingly wider pulses, transforming said series of increasingly wider pulses into a series of respective ramp pulses of increasing height, generating a series of drive pulses corresponding to the increasingly higher ramp pulses for driving the light emitter, monitoring the respective output signal's value until it reaches a predetermined value, fixing the width of one of the increasingly wider pulses corresponding to said predetermined value, storing the pulse of the fixed width for restoring the fixed width of the pulse in the situation of power outage immediately after the power up, and removing the calibration document from the document feed path; and wherein the operation cycle comprising the steps of: generating pulses of the fixed width determined in the calibration cycle, transforming the pulses of determined width in the calibration cycle into ramp pulses, each ramp pulse having a peak time, generating drive pulses corresponding to said ramp pulses, wherein each ramp pulse starts from the same voltage level, wherein said drive pulses are not generated until the peak time of the respective ramp pulse; and monitoring the output signal corresponding to at least one document in the document feed path, comparing the output signal with a required value, indicating a double-feed document condition if the monitored output signal exceeds the required value, counting a prolongation of the detected double-feed document condition, detecting a "true" double if the prolongation of the double-feed document condition exceeds the predetermined value, double-feed document condition including a first and a second overlapped documents, measuring a distance between a front edge of the first overlapped document and a rear edge of the second overlapped document, and detecting a double-feed document condition if said distance exceeds a predetermined distance, wherein the predetermined distance may be set up for various document sizes and speeds of the documents motion.