Paper feeder

Abstract

A sheet feeding apparatus includes a sending element of an ultrasonic sensor for outputting ultrasonic waves, a drive circuit for supplying the sending element of the ultrasonic sensor with a drive signal for driving the sending element, a receiving element of the ultrasonic sensor disposed opposite the sending element of the ultrasonic sensor across a sheet transfer path in the sheet feeding apparatus, and for receiving the ultrasonic waves, a setting unit for setting a threshold for the detection of transfer of the plurality of paper sheets by using the output of the receiving element of the ultrasonic sensor at the time of stopping of the output of the sending element of the ultrasonic sensor as a basic value, and a detection unit for detecting transfer of the plurality of paper sheets by comparing the output of the receiving element of the ultrasonic sensor with the threshold.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention generally relates to a sheet feeding apparatus, and particularly to a sheet feeding apparatus which sets a threshold that enables, in double feed detection using ultrasonic waves, the double feed to be detected without fail even in a case that the sensor output is varied by fluctuations in the sensitivity or sound pressure of the ultrasonic sensor and the like. [0003] 2. Description of the Related Art [0004] For use in the front shield device of a sheet-fed press, for example, an ultrasonic detector is known, which detects the transfer or feeding of a plurality of (for example, two) paper sheets (double feed or DF) by using ultrasonic waves. In this ultrasonic detector, ultrasonic waves outputted from a sending element of an ultrasonic sensor are received by a receiving element of the ultrasonic sensor, and it is detected whether there is one fed paper sheet or more according to the level (wave height...

AI Technical Summary

Benefits of technology

[0007] It is an object of the present invention to provide a sheet feeding apparatus in which a threshold permitting secure detection of double feed even when there are variations in the ultrasonic sensor output due to fluctuations in the sensitivity or sound pressure of the ultrasonic sensor.

[0009] According to the sheet feeding apparatus of the present invention, since the threshold for detecting transfer of a plurality of paper sheets is set by referencing the output of the receiving element of the ultrasonic sensor at the time of stopping of the output of the sending element of the ultrasonic sensor, the threshold (decision slice value) so set is not fixed. Therefore, it can follow variations in the environment of detection (for example, variations in the sheet feeding apparatus) or in the ultrasonic sensor's own characteristics (for example, aging) and, even after shipment, double feed in the sheet feeding apparatus can be always detected accurately. That is, even in a case that the sensor output varies with fluctuations in the sensitivity, sound pressure or fitting (accuracy) of the ultrasonic sensor, its ambience or adhesion of paper powder, double feed can be detected without fail.

[0012] According to the sheet feeding apparatus of the present invention, the output value of the receiving element of the ultrasonic sensor is adjusted either by altering the reference voltage of the operational amplifier or altering the frequency of clocks supplied by the drive circuit or the duty ratio. Therefore, at the time of shipping the sheet feeding apparatus, for example, there is no need to adjust the amplification rate of the amplifier of the ultrasonic receiving circuit with a variable resistance. This is also true at the time of replacing the ultrasonic sensor, for example. Even in a case that the ultrasonic receiving circuit comprises a band pass filter, the output of the receiving element of the ultrasonic sensor can be prevented from attenuating.

Problems solved by technology

Moreover, readjustment is needed when ultrasonic sensor has run into trouble and is to be replaced.

Further, in a case that the control is such as to determine the decision slice value uniquely, it is difficult to secure a sufficient margin of operation against variations in the ultrasonic sensor output due to fluctuations in the sensitivity of the ultrasonic sensor or its fitting to the feeding apparatus, ambience or adherence of paper powder.

Therefore, it may be impossible to detect double feed when paper sheets of different thickness are consecutively carried.

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