Image forming apparatus having looped belt and method of detecting index

摘要

An image forming apparatus includes an endless belt, an index provided at part of an end edge of the belt, a detecting member, a processing unit, and a storage unit. The detecting member changes an output value thereof based on the passing states of the index and the end edge of the belt in a detection area of the detecting member. The processing unit processes the output value and determines whether the index is present in the detection area by comparing the present output value with a threshold value. The storage unit stores the processed output value. The processing unit acquires a reference value based on the stored output value. The processing unit, when determining whether the index is present in the detection area, sets as the threshold value a value obtained by changing the most recently acquired reference value by a predetermined value.

主权项

1. An image forming apparatus comprising:
an endless belt configured to be looped over a plurality of rollers so as to rotate; an index provided at a part of an end edge of the belt so as to rotate together with the belt; a detecting member configured to have a detection area thereof which is defined at a part of a rotational path of the index and the end edge of the belt, and to change an output value thereof based on the passing states of the index and the end edge of the belt in the detection area; a processing unit configured to obtain the output value of the detecting member at regular intervals, to process the obtained output value, and to determine whether or not the index is present in the detection area of the detecting member by comparing the present output value of the detecting member with a threshold value; and a storage unit configured to store the output value of the detecting member having been processed by the processing unit, wherein the processing unit acquires a reference value used to set the threshold value based on the output value of the detecting member obtained at regular intervals and stored in the storage unit, and, when the processing unit determines whether or not the index is present in the detection area of the detecting member, the processing unit sets as the threshold value a value obtained by changing the most recently acquired reference value by a predetermined value, and wherein the processing unit averages the individual output values of the detecting member output during a predetermined length of time so as to calculate a first average value, further averages a plurality of the calculated first average values so as to calculate a second average value, and acquires the reference value based on the second average value.