FIELD OF THE INVENTION AND RELATED ART

The present invention relates to a measuring device for measuring an image on a sheet, an image reading apparatus for reading image on information from the sheet, and an image forming system for forming the image on the sheet.

As a main criterion for evaluation, it is possible to cite a high image quality representing by an index such as graininess, in-plane uniformity, character quality, color reproducibility (including color stability), geometrical characteristic (front/rear registration), or the like. Japanese Laid-Open Patent Application (JP-A) 2009-53346 and 2013-54324 disclose that in an image forming system of an electrophotographic type, a color of an image on a sheet is measured by using a color sensor provided on a feeding passage along which the sheet on which the image is formed. By using such a color sensor of an in-line type, it becomes possible to automatically execute, as a series of operations, formation of the image, which is an object to be measured such as a color chart, on the sheet and setting of an image forming condition.

In order to measure the image on the sheet by the color sensor of the in-line type with high accuracy, it is important that a distance from the color sensor to the sheet is stable. JP-A 2014-131205 discloses a constitution in which in the case where measurement of a color is carried out by the color sensor, a passing position of the sheet is aligned with a focus position of the color sensor by pressing the sheet toward the color sensor side by a pressing roller opposing the color sensor.

Incidentally, in the constitution in JP-A 2014-131205, there is a need to provide the pressing roller and a mechanism for moving the pressing roller, thus leading to an increase in cost and upsizing of a device.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a measuring device, an image reading apparatus and an image forming system which are capable of improving measurement accuracy with a simple constitution.

According to an aspect of the present invention, there is provided a measuring device comprising: a first roller pair configured to feed a sheet; a colorimetric unit provided downstream of the first roller pair with respect to a sheet feeding direction and configured to measure a color of an image on the sheet; a second roller pair provided downstream of the colorimetric unit with respect to the sheet feeding direction and configured to be rotated at a peripheral speed higher than a peripheral speed of the first roller pair; a third roller pair provided downstream of the second roller pair with respect to the sheet feeding direction and configured to feed the sheet; a motor configured to drive the first roller pair and the second roller pair; and a torque limiter configured to permit rotation of the first roller pair at a peripheral speed equal to the peripheral speed of the first roller pair in a state in which the sheet is nipped in both the first roller pair and the second roller pair, wherein the third roller pair is driven at a first speed before a trailing end of the sheet with respect to the sheet feeding direction passes through the first roller pair and is driven at a second speed higher than the first speed after the trailing end of the sheet passes through the first roller pair, wherein the first speed is set so as to be equal to the peripheral speed of the first roller pair; and wherein the second speed is set so as to be equal to a peripheral speed of the second roller pair in a state in which a slip of the torque limiter is not caused.

According to another aspect of the present invention, there is provided an image reading apparatus comprising: a first roller pair configured to feed a sheet; a reading unit provided downstream of the first roller pair with respect to a sheet feeding direction and configured to read image information of the sheet; a second roller pair provided downstream of the reading unit with respect to the sheet feeding direction and configured to be rotated at a peripheral speed higher than a peripheral speed of the first roller pair; a motor configured to drive the first roller pair and the second roller pair; and a torque limiter configured to permit rotation of the first roller pair at a peripheral speed equal to the peripheral speed of the first roller pair in a state in which the sheet is nipped in both the first roller pair and the second roller pair.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

