Paper conveyance device and method of controlling paper conveyance device

A paper conveyance device comprising:

• a paper feed unit that accommodates and supplies paper;
• a conveyance rotator that conveys the paper;
• a conveyance guide that guides the conveyed paper;
• a multi-feed detection unit that includes an ultrasonic sensor and a charge circuit;
• and
• a control unit into which a detection voltage that is an output of the multi-feed detection unit is input, wherein
• the ultrasonic sensor includes a transmission unit and a reception unit,
• the transmission unit transmits an ultrasonic wave,
• the reception unit outputs an electric charge corresponding to a level of a received ultrasonic wave,
• the transmission unit and the reception unit are provided on a paper conveyance path such that the paper is conveyed between the transmission unit and the reception unit,
• the charge circuit outputs, as the detection voltage, a voltage obtained by storing the electric charge output by the reception unit, and
• the control unit
• sets, for each sheet of the conveyed paper, a detection section in which the transmission unit is caused to transmit an ultrasonic wave,
• causes the transmission unit to transmit an ultrasonic wave in the detection section,
• sets a detection execution section and a detection skip section in the detection section,
• determines whether multi-feed is occurring based on the detection voltage in the detection execution section,
• does not determine whether multi-feed has occurred based on the detection voltage in the detection skip section,
• sets the detection skip section based on a time point at which vibration is applied to the conveyed paper, and
• sets a start time of the detection skip section based on a time point at which a downstream end portion of the conveyed paper in a paper conveyance direction hits against the conveyance guide.

A method of controlling a paper conveyance device, the method comprising:

• supplying paper from a paper feed unit that accommodates the paper;
• conveying the paper using a conveyance rotator;
• guiding the conveyed paper using a conveyance guide;
• providing a transmission unit and a reception unit of an ultrasonic sensor on a paper conveyance path such that paper is conveyed between the transmission unit and the reception unit;
• using, as the detection voltage, a voltage obtained by storing an electric charge output from the reception unit corresponding to a level of an ultrasonic wave received by the charge circuit;
• removing an electric charge of the charge circuit using the switch;
• setting, for each sheet of the conveyed paper, a detection section in which the transmission unit is caused to transmit an ultrasonic wave;
• causing the transmission unit to transmit an ultrasonic wave in the detection section;
• setting a detection execution section and a detection skip section in the detection section;
• determining whether multi-feed is occurring based on the detection voltage in the detection execution section;
• skipping determining whether multi-feed has occurred based on the detection voltage in the detection skip section;
• setting the detection skip section based on a time point at which vibration is applied to the conveyed paper;
• alternately performing first processing and second processing in the detection execution section;
• charging the charge circuit with the switch turned off and acquiring the detection voltage when performing the first processing;
• discharging the charge circuit with the switch turned on when performing the second processing;
• completing discharge of the charge circuit with the switch turned on prior to a time point of switching from the detection skip section to the detection execution section;
• and
• starting the first processing at a time point at which the detection section becomes the detection execution section.