In the prior art as presented by U.S. Pat. No. 5,546,165, by Rushing et al, there is disclosed an electrostatographic copier/printer with adjustable process control parameters wherein image contrast and color balance can be adjusted. The process control parameters considered adjustable are initial or primary charge, V.sub.o, exposure E.sub.o and developer bias V.sub.B.
The copier/printer described in Rushing et al is specifically directed to overcoming the problem of non-uniformities in reproductions that are associated with a direction that is cross-track to the process direction. Such non-uniformities cannot be well accommodated by making overall process changes.
In order to overcome this problem, the copier/printer described in Rushing et al provided for the printing of special test images. These printed test images are then delivered and fed into a scanner. The scanned data are analyzed to characterize the overall process in terms of cross-track uniformity and deviation from desired tone scale. The Rushing et al patent recognizes that cross-track nonuniformity and deviation from desired tone scale may result from misalignment of one or more process stations for example an exposure station, a charging station or a development station. Thus, z-axis skewing (tilt) of the LED printhead and/or Selfoc lens which focuses light from the LEDs (light-emitting diodes) onto the photoconductive surface can provide for a non-uniformity. Other recognized potential problems are the tilt of the primary charger or non-parallelism of the development station relative to the photoconductor. The Rushing et al patent proposes that, as a result of the scanning, adjustments can be made in LED exposure on-time or driver current to correct for same.
A problem with the apparatus of the prior art is that a scanner is required to provide for correction for such non-uniformities. The tilt and bow non-uniformities are the most common and most objectionable.
In the printer art generally, it is also known to detect non-uniformities using a visual detection by an operator and correction can be provided by adjustment of signals to each of the recording elements. In this regard, reference may be had to U.S. Pat. No. 5,596,353.
A problem with the above apparatus is that where several thousand recording elements are arranged on the printhead, it becomes relatively cumbersome to provide the manual correction suggested in this patent except where only a relatively few recording elements require correction, a situation not typical in a tilt or skew or bow situation.
It is an object of the invention therefore to provide for an improved control of cross-track non-uniformity in a reproduction apparatus.
Accordingly, it is an object of the present invention to provide an electrostatographic copier and/or printer apparatus and method for adjusting for cross-track non-uniformities without the need of a scanner to scan a test print printed by the apparatus and without the need for an operator to identify specific recording elements and provide specific corrections to specific recording elements.