1. Field of the Invention
The present invention relates to appropriate control in highest density adjustment in an image forming apparatus, an image forming system, and an image formation control method.
2. Description of Related Art
Conventionally, in electrophotographic image forming apparatuses, the following matter has been known. That is, even if the weight of toner per unit area on a sheet (hereafter, referred to as a toner adhesion amount) is the same, if the kind of a sheet is different, the density (optical density of a finally-output image becomes different due to its influence.
For example, in a coated paper sheet, since the sheet surface is made smooth, the image density becomes high (dense), but in a coarse paper sheet, the image density tends to become low (thin). This is because the image density is greatly influenced by the degree of penetration of toner to a paper sheet at a fixing process in an image forming apparatus.
For this reason, in an image forming apparatus designed or adjusted such that the print density standard is determined based on a sheet which easily exhibits an image density, such as a coated paper sheet, if an image is formed on a coarse paper sheet, a problem arises such that the image density becomes low.
Then, in the case where such a decrease of density exceeds a range capable of being solved by a density adjusting function provided to an ordinary image forming apparatus, a technique has been proposed to avoid such a problem by changing a toner adhesion amount in a range of a given level.
Further, different from the relative density adjustment in response to a difference in the kind of a sheet, there has been exists an absolute adjustment to make the highest density of an image forming apparatus become a reference value by using a predetermined reference sheet.
Some techniques with regard to adjustment of density in the electrophotographic image forming apparatuses have been disclosed in Japanese Unexamined Patent Publication Nos. 2012-189797 and 2009-139561.
Japanese Unexamined Patent Publication No. 2012-189797 has proposed a technique enabling to set a different toner adhesion amount for the same kind of a sheet so as to realize different color reproduction in response to a user's request. Further, Japanese Unexamined Patent Publication No. 2009-139561 has proposed a technique, at the time of using regular paper, to perform the highest density adjustment prepared for regular paper, and, at the time of using coated paper, to perform the highest density adjustment prepared for coated paper.
However, none of the above-mentioned patent publications proposes the absolute adjustment to make the highest density of an image forming apparatus become a reference value by using a predetermined reference sheet. In order to adjust the highest density in an image forming apparatus, a technique may be considered to perform adjustment in two stages separately into a highest density initial adjustment and a highest density automatic adjustment.
For example, in order to adjust the highest density in an image forming apparatus, at the initial time such as at the time of installing the image forming apparatus, the peculiar characteristic of a process unit is corrected. For this reason, a customer engineer determines a highest density reference as highest density initial adjustment. Subsequently, at an arbitrary time after the highest density initial adjustment, a user detects the density of an image density patch formed on a sheet by an image forming section with a density sensor, adjusts an image forming section so as to make the highest density coincide with a predetermined target density, and suppresses a characteristic change accompanying environmental fluctuation or the aged deterioration of a process unit.
In the highest density initial adjustment by a customer engineer and the highest density adjustment by a user, a calibration chart is formed on a sheet by image formation, a highest density portion (solid patch) on the calibration chart is detected by a density sensor, and each section of the image forming apparatus is adjusted until it is confirmed that a detection result is the desired density (toner adhesion amount). In the image forming section, an electrostatically charging voltage or a developing bias voltage is changed so as to increase or decrease a toner adhesion amount.
Incidentally, in the adjustment of the highest density, in order to administrate the highest density appropriately, a user is required in the highest density adjustment to use the same sheet and the same sheet setting used by the customer engineer at the time of determining a target density in the highest density initial adjustment.
Accordingly, when a user performs the highest density automatic adjustment, it is necessary to keep in mind the sheet and its sheet setting used by a customer engineer for the highest density initial adjustment. Further, at the time of the highest density adjustment by a user, it is necessary to perform a work to reproduce the sheet setting for the sheet used by a customer engineer for the highest density initial adjustment as a sheet profile. As a result, a problem arises in that it takes time to perform the work of the reproducing.
Further, if a mistake is made for the setting in the work of the reproducing, a problem arises in that it becomes impossible to adjust a desired highest density appropriately in an image forming apparatus. As described in the above, even if any kind of techniques are used, it has been quite difficult to perform adjustment so as to make the highest density of an image forming apparatus to the desired reference value.