A document feeding device includes a document placement unit at which a document is placed, a feeding roller for feeding the document, and a ranging sensor for measuring a distance to the document located most upward on the document placement unit. A control unit stops feeding the document by the feeding roller based on post-processing distance data obtained by statistically processing time series data of the distance measured by the ranging sensor.

An image forming apparatus including: a sheet feeding roller which feeds a sheet accumulated on a tray; and a hardware processor which: detects a movement speed of the sheet currently fed by the sheet feeding roller; and calculates a difference amount between the movement speed and a first reference speed, and determines a life of the sheet feeding roller based on the difference amount, wherein the hardware processor determines whether or not to use the movement speed of a first sheet for life determination based on a relationship between the movement speed of the first sheet and the movement speed of a sheet fed before the first sheet, and if the hardware processor determines not to use the movement speed of the first sheet for the life determination, the hardware processor calculates the difference amount by excluding the movement speed of the first sheet.

Method for controlling a sheet feeding device (1) comprising an elevator (2) for a stack of sheets, and an air supply system (3) configured to supply and direct one of more air streams towards an upper region (4) of the sheet feeding device for floating a plurality of upper sheets of the stack of sheets, wherein the elevator comprises a vertically movable support (5) for supporting the stack of sheets from below, wherein the sheet feeding device comprises an optical sensor (6) positioned adjacent the floated sheets for measuring light reflected from the floated sheets at a plurality of different heights, wherein the method comprises the steps of: continuously deriving from the optical sensor a density reading (DR) indicating the density of sheets floated, continuously deriving an average density (AD) based on a plurality of density readings, continuously deriving an upper density limit (UDL) based on the average density multiplied by a predetermined upper density limit factor (UDLF), continuously deriving a lower density limit (LDL) based on the average density multiplied by a predetermined lower density limit factor (LDLF), adjusting a first operating parameter (OP) of the sheet feeding device should the density reading exceed the upper density limit, wherein the adjustment of the first operating parameter is such as to decrease the density of floated sheets, and adjusting the first operating parameter of the sheet feeding device should the density reading subceed the lower density limit, wherein the adjustment of the first operating parameter is such as to increase the density of floated sheets. Also, a sheet feeding device connected to a controller configured to operate according to this method.

Method for controlling a sheet feeding device (1) comprising an elevator (2) for a stack of sheets, and an air supply system (3) configured to supply and direct one of more air streams towards an upper region (4) of the sheet feeding device for floating a plurality of upper sheets of the stack of sheets, wherein the elevator comprises a vertically movable support (5) for supporting the stack of sheets from below, wherein the sheet feeding device comprises an optical sensor (6) positioned adjacent the floated sheets pot for measuring light reflected from the floated sheets at a plurality of different heights, wherein the method comprises the steps of: continuously deriving from the optical sensor a density reading (DR) indicating the density of sheets floated, continuously deriving an average density (AD) based on a plurality of density readings, continuously deriving an upper density limit (UDL) based on the average density multiplied by a predetermined upper density limit factor (UDLF), continuously deriving a lower density limit (LDL) based on the average density multiplied by a predetermined lower density limit factor (LDLF), adjusting a first operating parameter (OP) of the sheet feeding device should the density reading exceed the upper density limit, wherein the adjustment of the first operating parameter is such as to decrease the density of floated sheets, and adjusting the first operating parameter of the sheet feeding device should the density reading subceed the lower density limit, wherein the adjustment of the first operating parameter is such as to increase the density of floated sheets. Also, a sheet feeding device connected to a controller configured to operate according to this method.

A document feeding device includes a document placement unit at which a document is placed, a feeding roller for feeding the document, and a ranging sensor for measuring a distance to the document located most upward on the document placement unit. A control unit stops feeding the document by the feeding roller based on post-processing distance data obtained by statistically processing time series data of the distance measured by the ranging sensor.

The measured winding diameter values Ds1(d) corresponding to the conveying distance d are measured by measuring the diameter of the printing medium M wound on the unwinding roll 71 by the diameter sensor 77. The measured winding diameter values Ds1(d) are smoothed by the low-pass filter to extract the smoothed winding diameter values Ds_avg1(d). By calculating the value of the diameter based on the initial diameter value Do1, the thickness value Tm and the conveying distance of the printing medium M, the calculated winding diameter values Dc1(d) are calculated. An operation of calculating the difference Ddiff1(d) between the calculated winding diameter value Dc1(d) and the smoothed winding diameter value Ds_avg1(d) while compensating for the delay by the low-pass filter is performed whereby the differences Ddiff1(d) are calculated. The calculated winding diameter value Dc1(d) are corrected by the differences Ddiff1(d).

An image forming apparatus including: a sheet feeding roller which feeds a sheet accumulated on a tray; and a hardware processor which: detects a movement speed of the sheet currently fed by the sheet feeding roller; and calculates a difference amount between the movement speed and a first reference speed, and determines a life of the sheet feeding roller based on the difference amount, wherein the hardware processor determines whether or not to use the movement speed of a first sheet for life determination based on a relationship between the movement speed of the first sheet and the movement speed of a sheet fed before the first sheet, and if the hardware processor determines not to use the movement speed of the first sheet for the life determination, the hardware processor calculates the difference amount by excluding the movement speed of the first sheet.

The measured winding diameter values Ds1(d) corresponding to the conveying distance d are measured by measuring the diameter of the printing medium M wound on the unwinding roll 71 by the diameter sensor 77. The measured winding diameter values Ds1(d) are smoothed by the low-pass filter to extract the smoothed winding diameter values Ds_avg1(d). By calculating the value of the diameter based on the initial diameter value Do1, the thickness value Tm and the conveying distance of the printing medium M, the calculated winding diameter values Dc1(d) are calculated. An operation of calculating the difference Ddiff1(d) between the calculated winding diameter value Dc1(d) and the smoothed winding diameter value Ds_avg1(d) while compensating for the delay by the low-pass filter is performed whereby the differences Ddiff1(d) are calculated. The calculated winding diameter value Dc1(d) are corrected by the differences Ddiff1(d).

A method for reducing the effects of variations in an unwinding, convolutely wound roll of web material is disclosed. The method utilizes the steps of: a. selecting a reference objective relating to a downstream operation, b. choosing at least one feedback device correlated to the reference objective, c. collecting process data from the at least one feedback device at different positions within a time-varying operation cycle for at least one operation cycle at a learning speed, d. calculating an error as the difference between the collected process data from step (c) and a reference signal related to the selected reference objective, e. generating a correction signal based upon the calculated error from step (d) and, f. applying the correction signal to the actuator during a succeeding time-varying operation cycle.