Technological Field
The present disclosure relates to a technique for estimating the basis weight of a sheet being conveyed in an image forming apparatus.
Description of the Related Art
Image forming apparatuses such as multi-functional peripherals (MFPs) have been widely used. There are many types of sheets available for MFPs. To print appropriately irrespective of the sheet type, control parameters such as sheet feeding speed, transfer voltage, and fixing temperature are set in accordance with the sheet characteristics. Printing without appropriate settings of the sheet characteristics may deteriorate print quality and the like. As such, various techniques for accurately detecting the sheet characteristics have been developed.
In relation to this technique, JP 2007-107976 A discloses a sheet type detecting apparatus “capable of detecting the sheet type”. JP 2002-5610 A discloses a thickness detecting apparatus that is “mechanically simple and inexpensive and capable of detecting the thickness of a medium irrespective of the dielectric or optical properties of the medium without the need for maintenance”. JP 5-99605 A discloses a non-contact thickness detecting apparatus that “is not influenced by variation in a gap between a detection electrode connected to an electrostatic sensor and an object to be detected”. JP 2015-193473 A discloses an apparatus for detecting the thickness of the sheet while “removing the influence of the eccentricity of a roller as much as possible”. JP 2010-189137 A discloses an image forming apparatus “capable of determining the sheet type with the sheet stored in a sheet feed tray”. JP 2006-259589 A discloses an image forming apparatus that “has solved implementation issues”.
The basis weight of the sheet is an example of the sheet characteristics. The basis weight of the sheet represents the weight of the sheet per area. The unit of the basis weight of the sheet is expressed as “g/m2”. Since the basis weight of the sheet correlates with the thickness of the sheet, the basis weight of the sheet is used in the meaning similar to the thickness of the sheet.
The settings of the basis weight of the sheet influence the printing accuracy in particular. Printing without appropriate settings of the basis weight of the sheet may cause various issues such as jams, transfer failures, and fixing failures. Therefore, the basis weight of the sheet needs to be detected accurately. As a method for estimating the basis weight of the sheet, an estimation method using a capacitance sensor has been proposed. This estimation method is the application of the principle that the capacitance of the sheet correlates with the basis weight of the sheet.
The capacitance sensor is susceptible to the surrounding environment (e.g., temperature, humidity, and objects nearby). Accordingly, in a case where the basis weight of the sheet is estimated from the capacitance detected by the capacitance sensor, the estimation result of the basis weight varies depending on the surrounding environment. Detecting the basis weight of the sheet while reducing the influence of the surrounding environmental variations is not disclosed in JP 2007-107976 A, JP 2002-5610 A, JP 5-99605 A, JP 2015-193473 A, JP 2010-189137 A, or JP 2006-259589 A. Therefore, there is a need for a technique for accurately estimating the basis weight of the sheet irrespective of the surrounding environment.