Patent Application
20050244175
During the course of operation of a printing device, various print parameters can drift resulting in a degradation of print quality. It can therefore be desirable to perform calibration procedures to restore print parameters to a desired state.
Calibration procedures can be performed in a number of ways. To perform some calibration procedures, for example, one or more test patterns are printed on a media (e.g., a paper, an image transfer belt, etc). A densitometer or other sensing device is then used to measure the density of the printed test patterns. These measurements are then used to set printing parameters to the desired state.
A problem can occur, however, when a calibration procedure is performed that results in one or more print parameters not being properly set as this can result in undesirable print quality.
Printing devices are often designed to operate in a low-power mode in order to reduce the printer's power consumption during periods when the printing device is inactive (i.e., when the printing device is not being used for printing) for an extended period of time.
For ease of discussion, a printing device that is presently operating in a low-power mode may be referred to herein as being in an “inactive state”. Furthermore, a printing device that is turned off may also be referred to herein as being in an “inactive state”.
A printer that is presently printing or ready to start printing without a warm-up cycle may be referred to herein as being in a “print ready state”. Many printing devices are designed to move from an inactive state to a “print ready” state upon the occurrence of certain events. For ease of discussion, such an event may be referred to herein as a “wake-up” event. Many printing devices, for example, move to a print ready state upon being turned on. For these printing devices, therefore, a wake-up event is the event of turning the printing device on. Furthermore, many of these same printing devices also are designed to move from a low-power mode to a print ready state upon receiving a print job. Thus, a wake-up event for these printing devices can also be the event of receiving a print job.
It is also noted that some printing devices can perform a calibration procedure to set parameters that control maximum printing densities. For ease of discussion, such a calibration procedure may be referred to herein as a “maximum density calibration”. These same printing devices may also perform a calibration procedure in order to set parameters that control printed halftones. For ease of discussion, such a calibration procedure may be referred to herein as a “halftone adjustment calibration”. The HP COLOR LASERJET 5500 is an example of a printing device that can perform both a maximum density calibration and a halftone adjustment calibration.
For ease of discussion, the very first calibration procedure that a printing device performs after a wake-up event has occurred may be referred to herein as a “wake-up” calibration procedure. Many printing devices operate to perform a wake-up calibration procedure during a warm-up cycle and prior to moving into a print ready state.
Construction of an Exemplary Printing Device
As shown in
The sensor 114 may represent any suitable type of sensor for enabling the printing device 102 to measure the density of printed test patterns during a calibration procedure. Thus, for example, the sensor 114 may represent a densitometer, a calorimeter, a spectrophotometer, etc.
Input/Output (I/O) port 116 allows the printing device 102 to receive a print job from an external source (i.e., a personal computer) over a communication link (e.g., a network and/or a parallel cable). The control panel 117 provides a walk-up user a user interface to the printing device 102.
Construction of an Exemplary Print Engine
During a printing operation, the marking assembly 210 employs an EP process to place a color image on the ITB 208. The image may then be transferred from the ITB 208 to a media sheet which is transported through the print engine 112, by the media transport system 212, along media path 213.
As noted above, the marking assembly 210 employs an EP process to place an image on the ITB 208. Accordingly, the marking assembly 210 may include, for example:
As shown, the developer roller 308 is located in proximity to the photoconductor 211 (only a portion of which is shown) and is connected to an AC source 310 and a DC source 312.
Development Step of EP Process
As understood by a person skilled in the art, the EP process typically includes a development step in order to develop, with toner, a latent image present on a photoconductor. This typically involves transferring toner from a toner supply to the photoconductor.
In the present embodiment, for example, toner transfer from the toner cartridge 302 to the photoconductor 211 is achieved by rotating the development roller 308 while applying both an AC bias (via the AC source 310) and a DC bias (via the DC source 312) to the outer surface of the developer roller 308. This results in the electrostatically charged toner 304 being electrically attracted by an electrostatic potential difference between the toner 304 and the developer roller 308.
The electrostatic potential difference causes the toner 304 to collect onto the outer surface of the developer roller 308 and then to move to the surface of the photoconductor 211 so as to develop a toned image corresponding to the latent image on the photoconductor 211. During toner transfer, the stirring blade 306 may also be rotated in order to mix the toner.
It is noted for the later discussion that under some conditions, the performance of the development step can improve the subsequent printing performance of the toner. For example, assume the toner 304 is not used for an extended period of time (e.g., eight hours). The quality of the first print generated using the toner 304 may be relatively low as a result of the toner 304 initially having a low charge level. When a development step is performed to generate printed output, the performance of the toner 304 can improve as a result of the toner being charged as well as mixed. Eventually, as the development step is repeated, the printing performance of the toner 304 stabilizes.
Calibration Procedures
In the present embodiment, the printing device 102 may implement several different types of calibration procedures in order to set various printing parameters. For example, the printing device 102 can perform a maximum printing density calibration as well as a halftone printing density calibration. In each of these procedures, test patches are printed on the image transfer belt 208 and the sensor 114 is used to measure the density of each printed test patch. The sensor measurements are then compared to target values. Based upon the comparisons, various control parameters are set.
Initiation of Calibration Procedure
Thus, for example, at block 401 the printing device 102 may be turned off or in a low power mode. In the case wherein the printing device is turned off, the wake-up event may be the event of turning the printing device 102 on. In the case wherein the printing device 102 is presently in a low power mode, the wake-up event may be the printing device 102 receiving a print job.
In response to the wake-up event, the printing device 102 proceeds to perform a warm-up cycle (block 404). This results in the printing device 102 moving from the inactive state to a print ready state.
At block 406, the printing device 102 counts the pages that are printed since the occurrence of the wake-up event. At block 408 and block 410, the printing device 102 operates to determine when the following criteria are satisfied:
Once the above two criteria are satisfied, the printing device 102 responds to this condition by automatically initiating a wake-up calibration procedure (block 412). The printing device may initiate, for example, a maximum density calibration procedure or a halftone density calibration procedure or both at block 412.
It is noted that performing a wake-up calibration procedure after a threshold number of pages are printed can be advantageous for a number of reasons. For example, assume the printing device 102 has not been used prior to the wake-up event for an extended period of time (e.g., eight hours). Printing pages prior to performing a wake-up calibration can improve, as well as stabilize, the printing performance of the toner supplies. As a result, the accuracy of the wake-up calibration can be improved.
It is further noted that the pre-determined number (N) of pages at block 408 may be selected with the following goals in mind:
Thus, for example, if goal #1 can be achieved with a reasonable degree of certainty after fifty or more pages are printed, the value of N may be set to fifty (as opposed to a higher number) so that the wake-up calibration is performed as soon as the toner in each supply is adequately conditioned and printing performance stabilizes.
It is noted that in other embodiments, the printing device 102 may automatically initiate a wake-up calibration when different or additional criteria are met. The printing device 102 may initiate a wake-up calibration based upon the number of times the developer roller 308 rotates. According to one embodiment, for example, the printing device 102 initiates a wake-up calibration in response to the developer roller 308 rotating a threshold number of times after the occurrence of a wake-up event.
In yet another alternative, the printing device 102 initiates a wake-up calibration only after all the following criteria are satisfied:
Note that criteria #2 would help ensure that each of the C, M, Y and K toner supplies was indeed used for printing and thereby conditioned prior to performing the wake-up calibration procedure.
It is further noted that in some embodiments a user may direct the printing device 102 to initiate a calibration procedure at any time after a wake-up event has occurred. For example, a user may initiate a wake-up calibration by inputting the appropriate request via the printer control panel 117.
It is further noted that the present invention may be embodied in the form of a “computer-readable medium”. As used herein, the phrase “computer readable medium” can refer to any medium that can contain, store or propagate computer executable instructions. Thus, in this document, the phrase “computer-readable medium” may refer to a medium such as an optical storage device (e.g., a CD ROM) or a magnetic storage device (e.g., a magnetic tape). The phrase “computer-readable medium” may also refer to signals that are used to propagate the computer executable instructions over a network or a network system, such as the Public Internet.
Thus, a memory component (e.g., memory 108) that stores computer executable instructions (e.g., firmware module 110) may represent an embodiment of the invention. Furthermore, signals used to propagate the firmware over a communication link (e.g. an intranet, Public Internet, etc) may also represent an embodiment of the invention.
Although several specific embodiments of the invention have been described and illustrated, the invention is not to be limited to specific forms or arrangements of parts so described and illustrated. The invention is limited only by the claims and the equivalents thereof.
