Xerography represents one method of copying or printing documents, which can be performed by uniformly charging a charge retentive surface such as a xerographic photoreceptor belt (i.e., a type of substrate). This uniformly charged surface is then preferentially exposed in the desired image areas in order to create an electrostatic latent image of a desired original image. A developing material or a toner can be then deposited onto the latent image to form a developed image. The developed image is then transferred to a final substrate, such as paper. The residual developing material on the surface of the photoreceptor is then cleaned off and the photoreceptor belt surface is then recharged in preparation for the production of another image. Such a methodology is monochrome in nature due to the fact that each image is transferred directly from a photoreceptor to paper. Another approach to copying and/or printing involves the use of an intermediate belt system where one or more colors (e.g., four colors) can be transferred onto a belt and a single transfer to paper is then performed.
The mass of pigment (e.g., toner mass) on an intermediate transfer or photoreceptor belt can be sensed by a full width array (FWA) based sensing application. A belt edge sensor can be used to track the position of the belt with respect to a sensor. By tracking the position of the belt, it is possible to map the belt surface and utilize the map as part of a flat field algorithm to calibrate the FWA sensor signal. Many printing applications require the optical measurement of a toner mass on the belt surface, where the belt surface is not uniform.
A process sensor can be utilized to measure uniformity of the toner on the non-uniform belt substrate. The non-uniformities on the belt surface convolute with the measurement of the toner uniformity and thus the signal-to-noise ratio is reduced. The bare belt surface can be recorded and mapped ahead of time and this information can be used later to compensate the raw data, thereby increasing the signal-to-noise ratio. Such processing, however, requires a fairly precise registration between the measurement signal and the original bare-belt signal.
Once-around and belt-hole signals are commonly utilized to provide reference to a moving substrate such as a photoreceptor or a drum. The once-around signal can be used as a start trigger for data logging or capturing. In a xerographic application, the process patches and targets are often developed in an inter-document zone (IDZ) where the process sensor-sampling period is typically restricted to the IDZ. Thus, depending on the length of the intermediate transfer belt (ITB) and engine speed, there may be multiple inter-document zones for one complete belt revolution.
Typically, the intermediate transfer belts are seamless and the inter-document zone areas do not fall on the same region of the belt; rather, they propagate around the belt during a printing process. Hence, it is necessary to precisely register the data captured by a process sensor during the IDZ with an appropriate region of the bare-belt signal. Prior art printing applications typically utilize additional encoders or position sensors to track the belt movement and to register bare intermediate transfer belt signals to the signal measured for location of interest on the belt.
Based on the foregoing it is believed that a need exists for an improved method and system to register the bare intermediate transfer belt signal to the signal sensed in the region of interest (e.g. inter-document zone) without adding additional hardware.