Systems and methods for detecting the presence of metallic objects in media to be conveyed in a medium transport system are disclosed. One or more induction sensors are included in the medium transport system to detect the presence of metal in the transported media, with detection signals sent from the sensors to a system processing unit. An ultrasonic detector is employed in some embodiments to output another detection signal. One or more microphones may also be included, for detecting the sound created as the medium is being transported. The system processing unit analyzes various detection signals and analyzes computed sound values from the microphones, to determine the presence and location of metal in the media. A position jam detector may assist in determining jams of the media along the medium transport path.

A medium feeding device includes: a placement unit on which a medium is placed; a pair of edge guides that is provided at the placement unit such that the edge guides are movable in a medium width direction to guide edges of the medium in the medium width direction that is a direction intersecting a medium feeding direction; feeding rollers that feed the medium placed on the placement unit; a path state detection section that detects a detection value in accordance with a state of the medium feeding path; a guide position detection section that detects positions of the edge guides; and a control section that determines whether or not the detection value detected by the path state detection section has exceeded a threshold value.

A medium transport apparatus includes a medium transport path through which a medium passes, a path state detection section configured to output a detection value corresponding to a state of the medium transport path, a control section configured to compare the detection value output by the path state detection section with a threshold value for the detection value and determine whether an abnormal condition has occurred in the medium transport path, and a storage configured to store history information including the detection value acquired in the past, in which the control section changes the threshold value based on the history information.

A medium transport apparatus includes a medium transport path through which a medium passes, a path state detection section configured to output a detection value corresponding to a state of the medium transport path, a control section configured to compare the detection value output by the path state detection section with a threshold value for the detection value and determine whether an abnormal condition has occurred in the medium transport path, and a storage configured to store history information including the detection value acquired in the past, in which the control section changes the threshold value based on the history information.

A detection section that detects a value used for determining whether or not a jam of a paper sheet has occurred includes a sound detection unit that detects a sound and an auxiliary detection unit that detects a value different from the magnitude of a sound in the case where a jam of the paper sheet has occurred, and, in the case where the sound detection unit has detected a sound of a magnitude equal to or greater than a first threshold value, a control unit controls determines whether or not a jam of the paper sheet has occurred with reference to a detection result of the auxiliary detection unit, and controls a transport unit on the basis of a result of the determination.

A detection section that detects a value used for determining whether or not a jam of a paper sheet has occurred includes a sound detection unit that detects a sound and an auxiliary detection unit that detects a value different from the magnitude of a sound in the case where a jam of the paper sheet has occurred, and, in the case where the sound detection unit has detected a sound of a magnitude equal to or greater than a first threshold value, a control unit controls determines whether or not a jam of the paper sheet has occurred with reference to a detection result of the auxiliary detection unit, and controls a transport unit on the basis of a result of the determination.

A paper warping detection device includes an input tray, a processor, a first emitting element, a first receiving element and a first analog-to-digital converter. A first critical value is stored in the processor. The first emitting element is electrically connected with the processor. The first receiving element is disposed to the other side of the input tray. The first receiving element and the first emitting element face each other. When the first emitting element is switched on, the first emitting element emits first ultrasonic wave signals towards the first receiving element. The first analog-to-digital converter is electrically connected with the first receiving element and the processor for converting the first ultrasonic wave signals into first digital signals and outputting the first digital signals to the processor. The processor reads the first digital signals and compares the first digital signals with the first critical value.

A paper warping detection device includes an input tray, a processor, a first emitting element, a first receiving element and a first analog-to-digital converter. A first critical value is stored in the processor. The first emitting element is electrically connected with the processor. The first receiving element is disposed to the other side of the input tray. The first receiving element and the first emitting element face each other. When the first emitting element is switched on, the first emitting element emits first ultrasonic wave signals towards the first receiving element. The first analog-to-digital converter is electrically connected with the first receiving element and the processor for converting the first ultrasonic wave signals into first digital signals and outputting the first digital signals to the processor. The processor reads the first digital signals and compares the first digital signals with the first critical value.

A sheet feeding device comprises sheet storage for storing a sheet, a merging conveying unit for feeding the sheet from the sheet storage to an image forming apparatus, a transmitting element for transmitting an ultrasonic signal to the sheet conveyed on the merging conveying unit, and a receiving element for receiving the ultrasonic signal having passed through the sheet and outputting an output signal according to strength of the received ultrasonic signal. When the sheet is a Japanese paper, the sheet feeding device detects double feeding of the sheet according to an average value of a plurality of the output signals and variation in a plurality of the output signals obtained for the one sheet. If the sheet is not double fed, the sheet is fed to the image forming apparatus. If the sheet is double fed, the sheet is discharged to the escape tray.

A sheet feeding device comprises sheet storage for storing a sheet, a merging conveying unit for feeding the sheet from the sheet storage to an image forming apparatus, a transmitting element for transmitting an ultrasonic signal to the sheet conveyed on the merging conveying unit, and a receiving element for receiving the ultrasonic signal having passed through the sheet and outputting an output signal according to strength of the received ultrasonic signal. When the sheet is a Japanese paper, the sheet feeding device detects double feeding of the sheet according to an average value of a plurality of the output signals and variation in a plurality of the output signals obtained for the one sheet. If the sheet is not double fed, the sheet is fed to the image forming apparatus. If the sheet is double fed, the sheet is discharged to the escape tray.