Abstract:
An image quality analysis system is provided that allows highly accurate measurements of motion quality defects. The motion quality analysis process relies only on relative measurements, which can be performed sufficiently accurately with standard input scanners. The technique can therefore be incorporated in the image path of a copier or multi-function printer being tested to allow on-the-fly motion quality correction without the need for expensive, high precision measuring equipment. The system includes one or more digital test patterns provided in hardcopy form for providing one or more hardcopy test images, an input scanner that can scan the hard copy test image to form a digital raster image, and an image quality analysis module that receives information about the position of the digital raster image and produces test results relevant to determination of image quality analysis, particularly motion quality defects. The method is accurate and robust using relatively low-resolution CCD-based flat bed scanners, even in spite of their long-range positional errors.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     Motion quality problems can cause serious image quality degradation and therefore customer dissatisfaction. Identifying these problems involves measuring pixel placement accuracy with high precision. Techniques exist to do this, but they are laborious and require sophisticated and very expensive equipment. 
     2. Description of Related Art 
     It is well known that customer satisfaction can be improved and maintenance costs reduced if problems with copiers and printers can be fixed before they become serious enough to warrant a service call by the customer. While current technology exists to enable printers and copiers to call for service automatically when sensors detect certain operating parameters outside of permissible ranges, there is not a very comprehensive manner of detecting incipient system failure or automatically diagnosing when problems with image quality reach a level where human observers perceive a reduction in quality. This is caused not only by the large number of operating parameters that would need to be tracked, but also because these parameters are strongly coupled to one another. 
     One of the causes of image quality degradation is associated with motion quality (MQ) problems. A MQ problem is considered to be any source of inaccurate pixel placement anywhere on the printed page, and can occur in the process and/or transverse directions. This includes sources of positional error such as, for example: mechanical noise due to rough gears and bearings, drive shaft eccentricity, ROS polygon wobble, rough paper transport, etc. It does not include irregular motion that leads to color errors but not positional errors, such as that caused by development donor roll shaft eccentricity. 
     Because MQ problems can cause serious image quality degradation and therefore customer dissatisfaction, much effort is being expended in identifying and eliminating these problems. Identifying these problems involves measuring pixel placement accuracy with high precision. Techniques exist to do this, but they are laborious and require sophisticated and very expensive equipment. 
     From an engineering perspective, it would be preferable if the measurements could be done quickly and economically at the test site. However, access to high-precision measuring equipment at the site is difficult to obtain and cost-prohibitive. Moreover, for self-correcting printing systems, it is essential that the measurements can be done locally. Flat bed scanners are affordable and are already widely used for image quality evaluation. Moreover, in the case of a printer-copier or a multifunction device, a flat bed scanner is already part of the system. However, such flat bed scanners typically have unacceptably large positional errors over large distances, such as across a page. As such, one would not expect such a scanner to provide motion quality measurements over a large surface with much precision. Accordingly, there are problems with existing image quality analysis systems, particularly those used in the field. 
     SUMMARY OF THE INVENTION 
     There is a need for image output devices, such as printers and copiers, to have systems to identify problems with image quality. Applicants have found that to comprehensively and reliably measure the system performance of a printer or copier, the image quality of the output must be measured. It is most preferable to have such a device self-diagnose these problems. 
     There also is a need for a relatively inexpensive system and method to determine image quality errors in image output devices while at the site. 
     One exemplary embodiment of the systems and methods of the invention overcomes such problems by developing powerful diagnosing tools within a digital printer or copier for self-diagnosis and evaluation of image quality. Image quality analysis can be performed to monitor many aspects of the printed output of the printing system. Of particular importance to overall image quality is determination of motion quality errors. 
     In this embodiment, the system provides: one or more digital (or hardcopy, in the case of a copier) test patterns and one or more pre-printed patterns for providing one or more hardcopy output test images; an input scanner that can scan the hard copy test image to form a digital raster image; and an image quality analysis module that receives information about the position of the digital raster image and produces test results relevant to determination of image quality analysis, particularly motion quality defects. 
     The input scanner and image quality analysis module may form part of the image output device or may be stand-alone components used to test the device. Optionally, a communication module may be provided that is capable of contacting a service department or a more sophisticated diagnostic module if further analysis or service is necessary, depending on the outcome of the image quality analysis. Alternatively, information relating to motion quality defects may be used by a corrective procedure within the image output device being tested to calibrate the device to correct for detected motion defects. 
     The systems and methods of the invention allow highly accurate measurements that are robust in determining motion quality errors, even though the scanners being used are relatively low in precision. The motion quality process relies only on relative measurements, which can be performed sufficiently accurate with standard input scanners. The technique can therefore be used for quick, simple, on-site detection and/or correction of motion quality errors in a printer or digital copier without the need for expensive, high precision measuring equipment. 
     A special test pattern and measurement technique is used to allow highly accurate measurements of motion quality defects in an image output device that prints in monochrome or color. The method has been demonstrated to be accurate and robust using relatively low-resolution CCD-based flatbed scanners, even in spite of their long-range positional errors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described with reference to the following illustrative drawings, wherein like numerals refer to like elements and wherein: 
     FIG. 1 shows a typical digital copier machine having a user interface suitable for use with the invention; 
     FIG. 2 is a schematic diagram of a digital copier having a user interface for communicating with a remote diagnostic computer; 
     FIG. 3 is a flow chart showing an image analysis method according to the invention; 
     FIG. 4A is an exemplary pre-printed test pattern used by the invention; 
     FIG. 4B is an exemplary digital test pattern used by the invention; 
     FIG. 5 is a flow chart showing a process of preparing pre-printed and measured test sheets and using them in image quality analysis according to the invention; 
     FIG. 6 is an exemplary output from the digital copier based on the digital test pattern of FIG. 4; and 
     FIG. 7 is an alternative image output device and image analysis system according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An exemplary device to which automatic image quality analysis is to be performed will be described with reference to FIGS. 1-3. FIG. 1 shows an image output device, in particular a digital copier machine  10 , comprising a plurality of programmable components and subsystems which cooperate to carry out copying or printing jobs programmed through a touch dialog screen  42  of a user interface (UI)  11 . Internal operating systems of the digital copier  10  are disclosed in U.S. Pat. Nos. 5,038,319, 5,057,866, and 5,365,310, owned by the assignee of the present invention, the disclosures of which are incorporated herein by reference in their entirety. As such, no further detailed description thereof is necessary. Digital copier  10 , however, is merely representative of a preferred printing system to which the image quality determination is made. It should be understood that a loosely coupled printing or reproducing system is also applicable for use with the invention described herein, such as a printer or facsimile device. Moreover, while there may be benefits to use of the image quality analysis on a reproduction system, such as a digital copier having an integral scanner component, the invention also is applicable to a printer used in conjunction with a stand-alone scanner, such as a flatbed type scanner. 
     Referring to FIG. 2, operation of the various components of exemplary digital copier  10  is regulated by a control system which uses operating software stored in memory in the system controller  16  to operate the various machine components in an integrated fashion to produce copies and prints. The control system includes a plurality of printed wiring boards (PWBs), there being a user interface module (UIM) core PWB  18 , a scanner/imaging core PWB  20 , an input station core PWB  22 , a paper handling core PWB  24  and an output station core PWB  26 , together with various input/output (I/O) PWBs  28 . A shared line (SL)  30  couples the core PWBs  18 ,  20 ,  22 ,  24  and  26  with each other and with the electronic data node core  32 , while local buses  34  serve to couple the PWBs to the respective cores and to stepper and servo PWBs. Programming and operating control over digital copier  10  is accomplished through touch dialog screen  42  of UI  11 . The operating software includes application software for implementing and coordinating operation of system components. 
     Floppy disk port  38  provides program loading access to UIM core PWB  18  for the purpose of entering changes to the operating software, loading specific programs, such as diagnostic programs, and retrieving stored data, such as machine history data and fault data, using floppy disks. Hard disk  36  is used as a non-volatile memory (NVM) to store programs, machine physical data and specific machine identity information. One of the programs hard disk  36  may store is image quality analysis software that forms an image quality analysis module  70  used by the invention. Module  70  may also reside on a floppy disk used in floppy disk port  38 . 
     UIM core PWB  18  communicates with video engine  40  for driving a suitable visual display  42 , such as a CRT or flat screen of the user interface  11 . The UIM core  18  also has connected thereto a control panel I/O processor  44  and a generic accessories interface I/O processor  46 . The interface I/O processor  46  is in turn connected to a modem PWB  48 . The modem  48  provides communication between digital copier  10  and a communications channel, such as a public switched telephone network  50  to facilitate information transfer to and from a remote diagnostic computer  60 , which may also include image quality analysis module  70  as well as other diagnostic modules. 
     The information from the subsystem cores flows to and from the UIM core PWB  18 , which embodies software control systems including a user interface system manager and a user interface manager. The UI system manager includes a UI display manager subsystem for controlling the display of messages on the display  42 . A data manager subsystem provides data management to the UI system manager. 
     In a first embodiment of the invention, image quality analysis is performed by the process set forth in the flow chart of FIG.  3 . The process starts at step S 300  and advances to step S 310  where at least one specific digital test pattern is provided. At least one specific pre-printed hardcopy test pattern is also provided. Exemplary digital test patterns and pre-printed test patterns are illustrated in FIGS. 4A and 4B, and will be described in more detail later. Preferably, multiple different test patterns are used to analyze various components relevant to a determination of image quality. Flow then proceeds to step S 320  where a corresponding hardcopy output of the digital test pattern is generated on one of the pre-printed hardcopy test patterns. In the case of a digital copier, this can be done by placing the hardcopy original of the test pattern at scanner  20  and scanning it to form a digital test pattern, which can then be used as an input to output station  26  to form a hardcopy output. Regardless of whether the output device is a printer or a copier, the hardcopy output (FIG. 6) is generated on top of a pre-printed pattern instead of bare paper, such as the pre-printed page shown in FIG.  4 A. Then, flow advances to step S 330  where the hardcopy output is scanned by scanner  20  to form a digital raster image for analysis purposes. 
     After step S 330 , flow advances to step S 340  where the digital raster image may be acted on by pattern recognition software, which can be located within hard disk  36  or removable storage  38  and is associated with image quality analysis module  70 , to determine a precise location of various test elements within the scanned digital raster image. This software uses a Hough or similar transform to automatically detect locator marks on the image, such as the concentric rings provided on the four corners of the pre-printed test pattern of FIG. 4A. A suitable pattern recognition system for use with the invention can be found in U.S. Pat. No. 5,642,202 to Williams et al., owned by the assignee of the present invention, the disclosure of which is incorporated herein by reference in its entirety. Alternatively, or in conjunction therewith, the test pattern may include a script that signifies a particular test pattern. The copier machine  10  may have hardware/software to decipher the particular script embedded into the test pattern. The memory of the copier  10  may be provided with a file corresponding to each possible script detailing the contents of the script and associated test pattern, as well as detailing the particular image quality analysis routine to be used to measure a particular part of overall image quality. A more detailed description of such a scripted test pattern can be found in co-pending U.S. Ser. No. 09/450,182 to Rasmussen et al., filed concurrently herewith, entitled “Method to Allow Automated Image Quality Analysis of Arbitrary Test Patterns”, the subject matter of which is incorporated by reference herein in its entirety. 
     After step S 340 , the process flows to step S 350  where image quality analysis is performed on the test image using image quality analysis module  70 . From step S 350 , flow advances to step S 360  where a determination is made by the image quality analysis module  70  whether the image quality for this particular test image is acceptable. If it is, flow advances to step S 380  where the process stops. However, if the image quality is not acceptable, flow advances from step S 360  to step S 370  where a call can be made to a diagnostic facility. This call may be an automatic service call made through modem  48  for scheduling an actual service visit by a service technician to correct the noted problems. Alternatively, it may be preferable for this call to be to a more sophisticated diagnostic module  80  located locally or at the remote facility that can further analyze the image quality problem along with values from various sensors and settings on the copier  10 . This would provide corrective feedback to the digital copier  10 , such as through modem  48  when module  80  is remotely located, allowing the digital copier  20  to adjust itself within acceptable parameters. A specific preferable example of such a case when the copier  10  is provided with a diagnostic module is where flow always advances from step S 350  to S 370 , such that the diagnostic facility makes the decision whether corrective action is necessary, basing that decision on both the image analysis and image quality measurements in conjunction with data from sensors and settings. 
     Alternatively, the image quality analysis module  70  may be remote from image output device  10 . An example of which is illustrated in FIG. 7 where image output devices are in the form of two multi-functional printers  10 A,  10 B which are associated with a personal computer  60  through appropriate data cables. A flat bed scanner  20  is also associated with personal computer  60  and image quality analysis module  70  is in the form of software provided in personal computer  60 . This embodiment operates as the previous embodiment in that the printers  10 A,  10 B (which ever is being tested) are given a test pattern to generate a hardcopy output from. This hardcopy output is then placed in scanner  20  to generate the digital test image. This digital test pattern is then analyzed to determine image quality of the multi-function printer. 
     While shown in FIG. 7 to be loosely associated, the invention can also be practiced with completely discrete components, such as a separate printer, scanner and computer or other source for containing image quality analysis module  70 . In this case, the hardcopy output from the printer can be provided to a non-associated scanner for scanning. Then, the digital test image from the scanner can be stored or converted onto a portable recording medium, such as a floppy disk and provided to a non-associated computer having the image quality analysis module. 
     At least two test patterns are needed for the invention, one of them digital and one of them pre-printed. These two test patterns are referred to as the “digital” and the “pre-printed”, respectively. One suitable pre-printed test pattern is provided in FIG.  4 A and consists of a page with a series of sharply-defined marks, such as crosses, distributed over the entire page at a predefined spacing, such as 10 mm increments in both directions. Alternatively, each of the two lines forming the crosses can be replaced by series of parallel lines, or other geometrical arrangement. The pre-printed test pattern also preferably contains two or more locator marks, such as the concentric rings provided at each corner. One suitable digital test pattern is provided in FIG.  4 B and consists of a page with a series of sharply-defined marks, such as parallel line segments, distributed over the entire page such that they are interspersed between the crosses of the pre-printed test pattern. The four line segments in each location, shown in FIG. 4A, are appropriate for a process color output device with four primaries. In the case of a monochrome output device, there would be only one line segment in each location, and in the case of a highlight-color output device, there would be two or more line segments in each location. 
     A process of determining motion quality using such a test pattern will be described with reference to FIG.  5 . The process starts at step S 500  and advances to step S 510  where a plurality of test pages are printed on a desired substrate using a high-accuracy printer, such as a web-fed offset press. The marks are preferably made to cover the entire page. The exact placement of these marks is not critical, but it is highly desirable that the placement at least be accurately repeated on every test page. Once the plurality of test pages are printed, the process advances to step S 520  where the marks on at least a predetermined number of the test pattern pages are tested using precise measuring instruments, such as a scanning microdensitometer, to accurately measure the location of all of the marks relative to the page. If the measurements are highly repeatable, then it can safely be assumed that the entire batch of test pages will have the same relative positions for each mark. However, if it is not repeatable, each test page needs to be individually measured. 
     Then, flow advances to step S 530  where one of the pre-printed test pages (FIG. 4A) is fed into the paper path of the multi-function copier/printer whose MQ is being evaluated. This part of the analysis is performed on site. Data from the digital test pattern (FIG. 4B) is then used by the printer/copier in step S 540  to output a series of matching marks superimposed on the pre-printed test page, which matching marks should be nominally lined up with the pre-printed marks. An illustrative example of such is provided in FIG.  6 . 
     From step S 540 , flow advances to step S 545  where the printer&#39;s hardcopy output, containing both the pre-printed marks and the printer&#39;s marks, is then scanned on a flat bed scanner, which can be the integral scanner provided in the multi-function copier/printer. From step S 545 , flow advances to step S 550  where relative offsets between the pre-printed and subsequent marks are measured. This can be achieved, for example, in a manner similar to that used for color-color registration in co-pending U.S. Ser. No. 09/450,181 to Rasmussen et al., filed concurrently herewith, the subject matter of which is incorporated by reference herein in its entirety. Many flat bed scanners have poor positional accuracy over long range, but excellent positional accuracy over short range. However, since the relative offsets between the pre-printed and subsequent marks are likely to be on the order of 1 mm or less, they can be accurately measured with flat bed scanners. From step S 550 , flow advances to step S 560  where these relative offsets can be converted to position on the page because the exact position of the pre-printed marks is known. From these flat bed scanner measurements, one can extract quantitative information on motion quality errors, as well as position of the entire page relative to the paper. The process then stops at step S 670 . 
     Thus, with the invention, motion quality defects can be extracted using a rather low-quality scanner, preferably the scanner of the machine being tested so that on-site analysis can be performed. 
     The present invention has been described with reference to specific embodiments, which are intended to be illustrative and non-limiting. Various modifications can be made to the invention without departing from the spirit and scope of the invention as defined by the appended claims.