Automatic Adjustment Technology for Improved Document Quality
On-demand printing today requires high image quality, high productivity, high document quality, and flexibility to support more diverse document types. In order to meet these needs, we at Fuji Xerox are continuing to work on developing various types of technology for automatically adjusting images to be output.
Technology for automatically adjusting front-to-back registration
With the exception of some production printers, the conventional alignmentNote 1 adjustment process has been a time-consuming task. Operators have to visually check the gap in alignment of a test image using a ruler, calculate the adjustment values for each adjustment item, and then input the values into the device. Furthermore, when highly accurate alignment is needed, operators must repeatedly print test images and input adjustment values to precisely adjust the alignment. Moreover, the amount of time needed for adjustment depends on the proficiency of each operator, with some operators finding it difficult to perform the adjustment process at all.
To address these problems, Fuji Xerox has developed a technology to quickly and automatically adjust front-to-back registration. This technology simplifies the process of registration adjustment, automatically calculating the gap between the current values of each parameter and their ideal values by printing a measurement chart and scanning the printed chart using the scanner of the machine or the duplex automatic document feeder (DADF).
Fig. 1 shows an overview of the automatic front-to-back registration adjustment function. First, a measurement chart is printed. The chart is then scanned by the printer's scanner, and the obtained data is sent to our unique analysis program. The program analyzes the image to determine the current alignment status of the printer. Then, an adjustment value is automatically calculated and entered into the printer. The entered adjustment values are uniquely calculated for each combination of paper type and paper tray. This eliminates the need for the manual calculation of adjustment values and repetitive work that were required for previous models. Thus, this technology dramatically reduces the adjustment time compared with previous models, helping to improve customers' work efficiency as well as document quality (Fig. 2).
- Note 1 Alignment: The absolute position of an image rendered on paper
- Note 2 Adjustment time by a Fuji Xerox engineer not specializing in alignment adjustment
Automatic density uniformity adjustment technology
There have been various ways to adjust density uniformity over the horizontal direction of paper depending on the machine model. For production printers, for example, service engineers need to adjust each individual machine for density uniformity. Also, for some color multifunction devices for desktop publishing (DTP), adjustment for density uniformity takes time and money because it is a difficult task; users either have to separately purchase a measurement device or call engineer services. To address these problems, Fuji Xerox has developed a technology to automatically adjust density uniformity. This technology simplifies the processes of density uniformity adjustment by calculating the optimal adjustment value using an image scanned by the printer's scanner.
Fig. 3 shows an overview of the automatic density adjustment function. First, measurement charts are printed. Separate measurement charts are printed out for CMYK adjustment and RGB adjustment. Then, the printer's scanner determines the status of density uniformity of the printed CMYK chart, followed by that of the RGB chart. After scanning, our unique analysis program analyzes all 16 colorsNote 3 including primary (CMYK) and secondary (RGB and gray) colors, then automatically calculates the adjustment value for obtaining an optimal image. This adjustment value is applied to the printer.
The adjustment algorithm is as follows. Conventionally, density uniformity adjustment has been performed by customer engineers. They have to visually check and adjust the density uniformity of each color separately. With this method, it is difficult to find the optimal adjustment value for all 16 colors. For example, when one color is adjusted to its optimal value, the quality of the other colors is degraded (Fig. 4: conventional method). However, because our unique analysis program automatically calculates the density uniformity of all 16 colors at the same time, it is now possible to calculate the optimal values to minimize differences in color and maintain the total balance of density of both primary and secondary colors (Fig. 4: new method).
Based on the adjustment value calculated by the analysis program, the amount of laser exposure for printing images is automatically modified to adjust density uniformity.
- Note 3 There are 16 colors because density adjustment is performed for each of the primary (CMYK) and secondary (RGB and gray) colors at both 20 percent and 60 percent standard density used on the test pattern.
Technology for adjusting the offset of second transfer voltage
For production printers, the toner transfer efficiency for each of the various types of paper used in the market can be improved by adjusting the second transfer voltage to the optimal value for each type of paper. To adjust the second transfer voltage, the operator (a system administrator) can select either "Auto" or one of two other methods: "Select Sample Number," which allows the operator to visually check a sample and select one of the preset adjustment values (ranging from -5 to +10), and "Enter Percentage," which allows the operator to manually enter a voltage ranging from 10% to 300% of the default setting. Adjusting the voltage to the optimal value using either of these two methods requires operators to have adjustment experience, because they must visually determine the optimal adjustment level. This leads to issues such as variation in the amount of time necessary for operators of different skill levels to make the adjustments, as well as variation in the accuracy of adjustment values set by different operators.
To address this, Fuji Xerox developed a new function within "Select Sample Number," the method that involves choosing the optimal adjustment value from among preset values. This added function makes it possible to automatically adjust the voltage to the ideal value, even if the operator has no experience.
Fig. 5 shows an overview of this second transfer voltage offset adjustment function. First, a measurement chart is printed on the paper which the users intend to use. This measurement chart is then scanned, and based on this scanned data, the machine determines the optimal transfer voltage based on the paper's basis weight and type, then automatically selects the most appropriate adjustment value from among the preset values (ranging from -5 to +10). In this way, the optimal transfer voltage can be set automatically even for special types of paper, thus achieving superior image quality.
Printhead streak adjustment technology
One of the image quality issues occurring in multifunction devices is density non-uniformity in the form of vertical streaks the same width as the printhead's SLED chips (each of which contains a large number of exposure elements). Due to variation in each SLED chip's exposure element characteristics and its rate of decline of light intensity over time, the light intensity between the SLED chips becomes uneven, causing this defect. To address this, Fuji Xerox has developed printhead streak adjustment technology which can be used to adjust the light intensity of SLED chips in a short amount of time. This is done by scanning a correction chart on the multifunction device, which then uses the chart to automatically calculate the adjusted light intensity for each chip in the printhead.
The process of the printhead streak adjustment technology is as follows. First, a correction chart is printed on the multifunction device. The chart is then scanned on the device’s scanner, and the obtained RGB data for each chip is analyzed with our original analysis program. The adjusted light intensity for each chip is calculated from the analysis results and applied to the printhead. With this technology, it becomes possible to make adjustments for image quality issues caused by printhead streaks. This contributes to reducing the time required to respond to image quality issues compared to previous models, as well as preserving high image quality.
Spot and streak diagnostics
Until recently, responding to issues concerning image quality was a time-consuming procedure due to the necessity for customer engineers (CEs) to physically attend customer workplaces to determine the causes of defects, as well as calibrate machines and replace parts. To address this problem, Fuji Xerox has developed a technology enabling the device itself to diagnose spot and streak defects occurring in printed images. The diagnostics function works by first printing out separate CMYK and blank measurement charts, which are then scanned in the duplex automatic document feeder (DADF). Following this, the scanned images are analyzed by the device to determine the location, size, density, and other characteristics of any spots and streaks found. The data obtained is then sent to an external server, from which CEs can remotely confirm the diagnosis results and the state of the fault. This technology makes it possible for CEs to identify the causes of defects and determine components in need of replacing in advance of their visit, thus further increasing accuracy and efficiency in fault resolution.