Various exemplary details are described with reference to the following figures, wherein:
Many modern multi-color image firming devices build up an image on an intermediate transfer member and then transfer the color image in one step to a media substrate, such as paper. Such image forming devices include, for example, photocopiers, laser printers, facsimile machines and the like. Examples of these include U.S. Pat. Nos. 4,791,452; 4,998,139; and 4,833,503, the disclosures of which are incorporated herein by reference in their entireties.
These image forming devices employ an imaging member such as a photoreceptor that is electrostatically charged, and then exposed to a light image corresponding to an image to be printed so that the imaging member is selectively discharged in accordance with the image. Thus, exposure of the imaging member records an electrostatic (latent) image on it corresponding to the informational areas contained within the image to be printed. This latent image is developed by bringing a developer material (liquid or powder) into contact with the latent image to form a toner image. The toner image recorded on the imaging member is then transferred to an intermediate transfer member, such as an intermediate belt or drum. The intermediate transfer member is transported past the imaging member to receive the toner image by pressing the intermediate transfer member against the toner image on the imaging member to receive the toner image therefrom. The intermediate transfer member then further transfers the toner image to a receiving material, such as paper.
An example of this is illustrated in
The multicolor image is then transferred to receiving material 212, such as paper by corotron 258. The paper moves in the direction of arrow 214. Upon completion of transfer, the intermediate belt 250 may pass a cleaning station 260 prior to advancing to photoreceptors 210a-d as known in the art.
With the increase in use and flexibility of image forming devices especially color devices which print with two or more different colored toners, it has become increasingly important to monitor the toner development process so that increased print quality, stability and control requirements can be met and maintained. For example, it is very important for each component color of a multicolor image to be stably formed at the correct toner density because any deviation from the correct toner density may be visible in the final composite image. Additionally, deviations from desired toner densities may also cause visible defects in mono-color images, particularly when such images are half-tone images.
Most machines already have a mass sensor looking at the intermediate that is used for determining the mass per unit area transferred to the intermediate belt (TMA or DMA) from the four colors when internally generated patches are created on the photoreceptors for the individual colors and then transferred from the photoreceptor to the intermediate belt. The exposure and development parameters are then adjusted to keep this mass within a target range. For space reasons this sensor is usually located after the area where the image is transferred from the intermediate to paper. Although certain prior applications disabled transfer to allow the undisturbed image to reach the sensor for testing, embodiments enable transfer with the specific paper so readings reflect characteristics of the specific paper being transferred to.
With reference to
Known ETAC sensors are based on light scattering or reflecting from the patches on the surface of the intermediate transfer member. These sensors can look at both the specular and diffuse light coming from the patch as it is illuminated by a source. For color images at high density the diffuse image is able to record higher masses without saturating, but the specular signal will be more useful in looking at the low masses typical of the material remaining after transfer. While the light scattering based sensor is most likely to be the type used to measure the mass, this invention is not limited to a particular type of sensor but can be implemented with any type of sensor capable of detecting a small amount of toner on the intermediate.
An advantage of measuring the toner patch density on intermediate transfer belt 250 is that a single densitometer 290 can make a measurement for all colors (i.e., for the color patches formed by each photoreceptor) instead of using a separate mass sensor for each photoreceptor. Although DMA permits one to monitor the manner in which toner is deposited onto the imaging member, it does not provide a complete picture of the image formation process because DMA does not take into account the efficiency with which toner is transferred from the imaging member to the receiving material (e.g., paper) which ultimately receives the final image.
However, the same sensor can be used to look at an image after transfer if the transfer is enabled while the paper of interest is run through the machine. This will measure the extent of residual mass (RMA) remaining on the intermediate transfer member 250. Patches 400 for selected primaries, two color blends, and process black can be generated, developed, transferred to the intermediate. and transferred again to paper. The patches can be set up so that they align with the mass sensor just as the patches for TMA control. This eliminates the need for an additional sensor. Preferably, the patches would be set up so that a complete set fits within the width of a sheet, and transfer settings would be modified or swept between the feeding of each sheet. Thus you would need a number of trial sheets equal to the number of trial transfer settings to perform the testing. After each patch is transferred to the sheet, its RMA would be measured.
These measurements can be used by controller 300 to control various aspects of toner development and the transfer process. This may include, for example., set points for photoreceptor voltage potential, exposure levels, intensity levels, developer biases, developer bias frequency, bias transfer voltages, transfer current, etc.
The focus of the disclosure is on control and setting of second transfer parameters so that the second transfer is optimized. The best setting of the transfer parameters for the second transfer depends upon many factors, such as paper type and environmental conditions. When the transfer mechanism is a transfer corotron, the transfer parameter may include transfer voltage. When the transfer mechanism is a biased transfer roll, the transfer parameter may include transfer current. Look-up-tables to determine reasonable settings for several broad categories of paper under several humidity conditions typically provide acceptable transfer. However, there is no guarantee that these will be the optimal settings, and they can lead to transfer losses of 10% or more.
Certain image forming devices, such as for example the Xerox 7750 multicolor copier, have a provision for adjusting transfer parameters in a step fashion. Although this particular device only allows manual stepping through parameter settings, embodiments could include software or hardware to automate the stepping through one or more transfer parameter ranges in accordance with the disclosed methods of testing.
The basic testing methodology is to sweep the transfer parameter, such as voltage or current, through a suitable range while a set of patches is developed and transferred to the particular paper of interest. For example, when the transfer mechanism is a corotron, the transfer parameter may be transfer voltage. When the transfer mechanism is a biased transfer roll, the transfer parameter may be transfer voltage. These patches would preferably be aligned with the suitable mass sensor and the parameter leading to minimum mass remaining on the intermediate member (and hence maximum transfer efficiency) is determined. Data may be generated with one, two, or more toner layers and a suitable weighed average may be used to determine the optimum setting.
In the case of the 7750 copier, nine setting adjustments are possible. When a single test patch is printed oil each sheet, this would result in a waste of nine sheets of paper to perform the testing and find an optimal setting. To save paper, possibly more than one set of patches could be fit within one sheet of paper as in
Because there is a cost to the process, an operator may only want to run the optimization when he intends to run the one paper for a long job or for several jobs in sequence. Also, the knowledge of current environmental conditions could be used to establish a range of settings to optimize over. For example, the highest five settings out of nine could be examined at low humidity and the lowest five settings could be examined at high humidity. Thus, it is advantageous to provide an image forming system that is capable of default operation for routine jobs, but has the capability of optimization if desired.
An exemplary process for optimizing the second transfer will be described with reference to
If the optimization mode is not set, flow advances to step S410 where default settings are used and the process is ended. However, if the optimization mode is set, flow advances from step S405 to step S420 where initialization occurs. This resets the current image transfer settings and sets one or more transfer parameters to a first value. Initialization may also include setting of a sampling rate N relating to the number of test samples and values to sweep through. Thus, N defines the sampling granularity of the testing. That is, the test parameter is varied from a lowest to a highest operating value, with a higher sampling rate resulting in a smaller incremental advance between each sampling. A sampling with N=3 would result in a low, a middle and a high value, whereas a sampling with N=9 would have the operating range divided into nine sampled values, with nine sheets of paper needed to find the optimum setting.
Although N could take any value, there is a tradeoff between optimization and efficiency. Because there is a cost and time associated with the process, an operator may select the level of optimization needed. For most purposes, a suitable N would be between 5-9 to attain a substantially optimized transfer setting. After that, there are diminishing returns, particularly when assessing multicolor print patches. To save paper, possibly more than one set of patches can be fit within one sheet of paper (as shown in
Also, the knowledge of the environmental conditions being experienced now can be used to determine the transfer setting range to be varied. For example, in a system where the parameter can be varied between 9 values, the highest five settings out of nine can be examined at low humidity and the lowest five settings can be examined at high humidity.
Once the parameters are initialized, flow advances to step S425 where a test patch is generated on the intermediate member as known in the art. For example, the intermediate member 250 may include one test patch 400 at page width intervals as in
From step S425, flow advances to step S430 where the test patch 400 is transferred from the intermediate transfer member to the media, such as a desired sheet of paper of any suitable type, as known in the art. Once test patch 400 is transferred, flow advances to step S435 where the residual mass of toner (RMA) on the intermediate member 250 in the test patch area is measured. Measurement can take various conventional or subsequently developed forms. Preferred embodiments rely on existing mass sensors provided on the image forming device to eliminate the need for additional sensors. Although simpler mass sensors could be used, preferred embodiments use an ETAC sensor, which provides a higher degree of accuracy. However, the invention is equally applicable to other methods such as vacuuming of the residuals from the intermediate member 250 for remote mass measurement using a scale.
From, step S435, flow advances to step S440 where it is determined whether additional samples are necessary. If so, flow advances to step S445 where the parameter value is incremented. From step S445, flow returns to step S425 where another test patch is generated.
If no further test samples are necessary, flow proceeds from step S440 to step S450 where a determination is made of the patch having the lowest RMA. When the transfer involves multiple color transfers, it may be desirable to determine the RMA of each individual color. Because each color could have differing transfer properties, the patch corresponding to the lowest RMA would be chosen based on an combination of color values and an associated weighting to achieve a composite optimization.
From step S450, flow advances to step S460 where the image forming apparatus transfer parameters are set based on the determined lowest RMA. For example, if there were nine test patches and the third patch had the lowest RMA, the transfer parameters would be set to the values used to generate the third test patch. From step S460, flow advances to step S470 where the process stops.
As is evident from the above discussions, this method is capable of optimizing transfer parameters without the need for any additional hardware, such as sensors, as it uses hardware already provided for other purposes. What is needed is the ability to controllably adjust one or more operating parameters relating to the transfer to sweep the parameter through several values within an operating range of values.
As shown by the graphs in
Just as another detector can be used to look at RMA, if a corotron or other device is used to transfer toner to paper, parameters relating to their operation could also be adjusted on the basis of the RMA to optimize transfer for a given paper type.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, nay be desirably combined into many other different systems or applications. For example, the test patches 400 may provide single color residual mass for testing or multiple layers for testing. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.