GB2384352A

GB2384352A - Method for tuning print engine operating parameters

Info

Publication number: GB2384352A
Application number: GB0306993A
Authority: GB
Inventors: Clayton E Chadez; Richard H Benear
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1998-10-20
Filing date: 1999-09-30
Publication date: 2003-07-23
Anticipated expiration: 2019-09-30
Also published as: GB2384352B; GB0306993D0

Abstract

A printer (22) performs both the processing and printing tasks efficiently using controller firmware (26) with a single data path (i.e., one ASIC). The printer has a periodic print cycle in which data for one page or plane (if multi-colored) is printed during each cycle. The print cycle is typically longer than the time needed to print one page or plane. Thus, the print cycle can be segmented into a "printing phase" in which the printing mechanism prints data, and a "non-printing" phase in which the printing mechanism does not print data. The controller firmware (26) interleaves printing operations with non-printing operations during the printing and non-printing phases of the print cycle, respectively. During the printing phase, the controller (26) is dedicated to printing a page or plane. During the non-printing phase, the controller is free to perform other tasks, such as compressing raster data for subsequent printing. The printer is configured with a set of operating parameters that enable the controller firmware to alternate between printing and non-printing tasks (e.g., data compression). Once released from manufacturing, the printer may, in practice, not perform optimally to the specifications. Thus, another aspect of this invention is to tune the operating parameters to achieve optimal performance for a specific printer. This tuning is a self-tuning technique that is performed in post-manufacture real-time, while the printer is in operation.

Description

PRINTER AND METHOD FOR ALTERNATELY PRINTING AND COMPRESSING DATA USING SAME PROCESSING UNIT TECHNICAL FIELD This invention relates to printers, such as laser and color laser printers.

More particularly, this invention relates to methods for alternately printing and compressing data during the same engine cycle using the same processing unit.

BACKGROUND A typical printer receives data from a host computer in a driver format, such as PCL or postscript. The printer converts the host data to a bitmap containing raster data for individual pixels to be printed. The printer compresses the raster data for storage and subsequently decompresses the raster data in real-time. The printer sends the raster data to the print engine, which prints the data onto a recording media.

Printer firmware must perform both compression and printing (or"video") operations. Ideally, these tasks are performed at the same time to preserve engine speed and overall printer throughput. With existing firmware and printing methods, one solution for achieving this ideal is to implement two application specific integrated circuits (ASICs), one to process the incoming host data and another to drive the print engine and printing mechanism to print the data.

Unfortunately, implementing a second ASIC in the printer firmware adds considerable expense to the printer.

Accordingly, there is a need to design printer firmware that performs both the processing and printing tasks using only one ASIC, while maintaining an acceptable engine speed.

SUMMARY This invention concerns a printer that performs both the processing and printing tasks efficiently using controller firmware with a single data path (i. e. , one ASIC). The printer has a periodic print cycle in which data for one page or plane (if multi-colored) is printed during each cycle. The print cycle is typically longer than the time needed to print one page or plane. Thus, the print cycle can be segmented into a"printing phase"in which the printing mechanism prints data, and a"non-printing"phase in which the printing mechanism does not print data.

For instance, in a laser printer, the non-printing phase is used for drum rotation to return the drum to the proper position for printing the next page or plane.

The controller firmware interleaves printing operations with non-printing operations during the printing and non-printing phases of the print cycle, respectively. During the printing phase, the controller is dedicated to printing a page or plane. During the non-printing phase, the controller is free to perform other tasks, such as compressing raster data for subsequent printing.

The printer is configured with a set of operating parameters that enable the controller firmware to alternate between printing and non-printing tasks (e. g. , data compression). Once released from manufacturing, the printer may, in practice, not perform optimally to the specifications. Thus, another aspect of this invention is to tune the operating parameters to achieve optimal performance for a specific printer. This tuning is a self-tuning technique that is performed in postmanufacture real-time, while the printer is in operation.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. I is a side view of a printing system having a printer and workstation.

Fig. 2 is a block diagram of the printing system.

Fig. 3 is a flow diagram showing steps in a general method for operating a printer.

Figs. 4 and 5 are timing diagrams showing an exemplary detailed operation of a color laser printer to interleave printing and compression tasks using the same controller.

Fig. 6 is a flow diagram showing steps in a method for tuning printer operating parameters.

The same reference numbers are used throughout the figures to reference like components and features.

DETAILED DESCRIPTION This invention relates to printers and is described in the context of laser printers, and particularly color laser printers. Aspects of this invention may also be implemented for other types of printers, such as inkjet printers and color thermal printers.

Exemplary Printins System Fig. 1 shows a printing system 20 having a color laser printer 22 connected to a host workstation 24 via a direct connection or over a network. The workstation 24 outputs host data to the printer 22 in a driver format, such as PCL or postscript. The printer 22 converts the host data to a bitmap containing raster data for individual pixels to be printed. The printer 22 then compresses the raster

data for storage. At print time, the printer decompresses the raster data in real- time and sends it to the engine where it is printed onto a recording media.

Fig. 2 shows the system 20 in more detail. The printer 22 has a controller 26 that processes and prints the host data. The controller 26 has a data processing unit or CPU 28, a volatile memory 30 (i. e., RAM), a non-volatile memory 32 (e. g., ROM, Flash). The printer 22 also has printing mechanism 34, such as a rotatable drum. In non-laser printers, the printing mechanism may have other embodiments, such as one or more print heads mounted on a shuttle carriage. The printer 22 also has a print engine 36 that is responsible for taking the raster data and causing the printing mechanism 34 to deposit a corresponding image onto the recording media.

The controller 26 controls operation of the printing mechanism 34 and the print engine 36. The controller's CPU 28 is preferably implemented as an Application Specific Integrated Circuit (ASIC) that is designed to support serial and parallel I/O functionality with the host, compress and decompress the raster data, communicate with the print engine, and send the host data to the engine.

The workstation 24 has a processor 40, a volatile memory 42 (i. - RAM), and a non-volatile memory 44 (e. g. , ROM, hard disk, floppy disk, CD-ROM, etc.).

The workstation 24 may be implemented, for example, as a general-purpose computer, such as a desktop personal computer, a laptop, a server, and so forth.

The workstation 24 implements a software-based printer driver 46 that is stored in non-volatile memory 44 and executed on the processor 40. The printer driver 46 configures print data into an appropriate format (e. g. , PCL, postscript, etc. ) and outputs the formatted data to the printer 22.

The printer controller 26 performs the dual task of processing the host data in preparation for printing and facilitating the actual printing of the data. Ideally, the printer would be configured with two controllers (i. e. , two ASICs), one to process the incoming host data and another to drive the print engine and printing mechanism to print the data. However, this ideal option is not desirable in the marketplace due to the expense of adding a second controller to the printer.

Accordingly, the printer of this invention is designed to perform both the processing and printing tasks efficiently using only a single controller 26. The printer has a periodic print cycle in which the data for one page or plane (if multi- colored) is printed during each cycle. The print cycle is typically longer than the time needed to print one page or plane. Thus, the print cycle can be said to have a "printing phase"in which the printing mechanism prints data, and a"non-printing" phase in which the printing mechanism is not printing data. For instance, in a laser printer, the non-printing phase is used for drum rotation to return the drum to the proper position for printing the next page or plane.

The printer interleaves printing operations with non-printing operations during the printing and non-printing phases of the print cycle, respectively. During the printing phase, the controller is dedicated to the task of printing a page or plane. During the non-printing phase, the controller is free to perform other tasks. The printer takes advantage of the non-printing phase to compress the raster data for a subsequent printing phase.

General Operation For discussion purposes, the general operation of a four pass color printer is described. The techniques described below are equally applicable to monochrome printers as well.

The print engine 36 of color printer 22 requires four"passes"or drum rotations for one color page. On each rotation of the drum, the printer deposits a plane of different color toner, such as Cyan, Magenta, and Yellow (CMY), onto an intermediate transfer device. During the last pass, the transfer device transfers all toner colors to the recording media.

The time taken by the printer to make all four passes depends on the engine speed. A conventional color laser printer employs a print engine that prints at a speed of four page per minute (ppm) or one page every 15 seconds. This means that the printer has a total of 3. 75 seconds available for each of the four passes.

In each pass, two operations are performed. First, the video data for the corresponding color plane is sent to the engine. Second, the intermediate transfer device rotates back to its starting position and the toner carousel rotates to its next position. Approximately two-thirds of the time is spent transferring data with the remainder to perform the setup for the next plane. For example, in an HP Laserjet color printer, approximately 2.28 seconds is used to send one full plane of color data for a normal 8. 5"xll" letter size paper. With each plane having a 3.75 seconds, this leaves approximately 1.47 seconds for each pass where the controller is not being used to facilitate printing, and therefore can be redirected to compress raster data.

Fig. 3 shows a flow diagram of the general steps in the printer operation of interleaving compression and printing tasks. At step 60, the color printer receives

data from the host computer. At step 62, the controller 26 converts the host data to raster data. At step 62, the printer determines whether it is in the printing phase or the non-printing phase of the print cycle.

When the printer is in the non-printing phase, the controller 26 performs compression tasks to compress the raster data that will later be used in the printing phase (step 66). According to an exemplary set of operating parameters, this task consumes approximately 1.37 seconds of the print cycle. Near the end of the non- printing phase, the controller 26 is reconfigured for the upcoming printing tasks (step 68), which takes approximately 0. 1 second of the print cycle.

When the printer is in the printing phase, the controller 26 facilitates the printing operation. The controller decompresses the previously compressed raster data on the fly (step 70) and directs operation of the print engine and drum to print the raster data (step 72). The printing operation consumes approximately 2.28 seconds of the print cycle.

According to this method, the printer controller 26 alternates between compression and printing operations, depending upon the phase of the print cycle.

While Fig. 3 provides a more general overview of the printer operation, Figs. 4 and 5 provide a detailed example of the printer operation of a color laser printer.

Exemplary Timing Illustration Figs. 4 and 5 show exemplary timing diagrams for operating a 4-ppm color laser printer. The printer makes four passes per page, as described above. Fig. 4 shows the four passes to deposit the three planes of color and transfer them to the recording media, and Fig. 5 shows the fourth pass in detail.

The"Top"signal 80 refers to the top of form when the controller 26 begins sending raster data to the print engine. The"PRNT"signal 82 instructs the print engine to begin. The"Plane Done"signal 84 identifies when the current plane, which began with the"Top"signal 80, is completed. The"Reconfigure"signal 86 establishes when the controller begins preparation for an upcoming printing phase.

The"Resource Free"waveform 88 demonstrates via the high conditions when the controller is available for activities other than printing, such as compression activities. More specifically, the controller 26 is free to perform compression activities during the interval between the plane done signal 84, when the printing operation for the plane is completed, and the subsequent reconfigure signal 86, when the controller prepares for the next plane.

With reference to Fig. 4, the first"Top"pulse at time A marks the start of the first plane of the first page. The controller begins sending data to the print engine at time A. It is noted that prior to the start of the first plane in this page, the print signal at time Y has already been triggered. At time B, the plane done signal 84 marks the completion of the plane. At time C, the reconfigure signal 86 instructs the controller to begin preparation of the upcoming printing phase, followed by the next top signal at time D. Time W marks the fourth and last top signal for the four-pass process and is shown here for reference to the timing diagram of Fig. 5.

The print cycle is defined by the time interval A-D; that is, the time between consecutive top signals 80 at times A and D. The time interval A-B designates the printing phase of the print cycle and the time interval B-D designates the non-printing phase of the print cycle. The controller 26 performs printing operations during the printing phase A-B. The controller 26 is then free

to perform other operations in the non-printing phase B-D. Continuing the above example, the print cycle A-D is approximately 3.75 seconds for normal 8. 5"xll" letter size paper, the printing phase A-B is approximately 2.28 seconds, and the non-printing phase B-D is approximately 1.47 seconds.

The non-printing phase B-D is segregated into a first interval extending from time B of the plane done signal 84 to time C of the reconfigure signal 86, and a second interval from time C of the reconfigure signal 86 to time D of the next top signal 80. During the first interval, the processor 26 performs non-printing operations such as data compression. During the second interval C-D, the processor 26 prepares for the upcoming printing operations. The first interval is approximately 1.37 seconds, whereas the second interval is approximately 0.1 second.

Fig. 5 shows the fourth pass in detail. It involves the interval from time W, the top signal 80 for fourth plane, to time A, the top signal 80 for first plane of next page. At time X, the plane done signal 84 marks the completion of the fourth plane. At time Y, the print signal 82 is triggered to mark the start of a next page. At time Z, the reconfigure signal 86 instructs the controller to begin preparation of the upcoming printing phase for the first plane of the next page, which begins at time A. In this timing diagram, the print cycle W-A contains a printing phase W-X and a non-printing phase X-A. The latter phase is separated into a first interval XZ, in which the controller performs compression operations, and a second interval Z-A, in which the controller prepares for the next page.

The time interval W-Z in Fig. 5 is based on the state of the print engine and can vary from 3.75 seconds to 15 seconds. Another advantage of this invention is

that most of this time is made available for non-printing operations (e. g., compression).

Real-time Tunis of Operating Parameters The above explanation assumes that the printer operates within its specifications. However, the printer may, in practice, not perform optimally to the specifications for a number of different reasons. Accordingly, another aspect of this invention is to tune the operating parameters to achieve optimal performance for a specific printer. This tuning is performed in post-manufacture real-time, while the printer is in operation.

Fig. 6 shows steps in a method for tuning the printer's operating parameters. At step 100, the printer is initially configured with a set of parameters. For example, the tunable parameters with respect to the timing diagram of Fig. 5 include a print cycle W-A, a printing phase W-X, a Top to Print interval W-Y, and a non-printing phase X-A (which includes a resource free interval X-Z and a reconfiguration interval Z-A). The tuning parameters are stored in non-volatile memory 32. Table 1 summarizes the tunable parameters.

Table 1

Parameter Value Print Cycle W-A 3.75 seconds Printing Phase W-X < 2. 28 seconds Top to Print Interval W-Y 2.50 seconds Non-Printing Phase B-D 1. 47 seconds - Resource Free Interval B-C 1. 37 seconds - Reconfiguration Interval C-D 0.10 second

At step 102, the controller 26 monitors operation of the printer and attempts to detect when one of the parameters is not in compliance. Non-compliance is defined by the manufacturer to a desired set of tolerance levels for each parameter. If a failure occurs as a result of one of these values being inaccurate or less than optimal, the controller determines which parameter is responsible for the failure (step 104).

For instance, if the print signal 82 fails to trigger within the 2.50 second window allowed by the Top to Print interval W-Y, the printer transitions to a cleaning cycle that lasts approximate 12 seconds. Thus, the print cycle W-A is expanded to 12 seconds. This adjustment is summarized as follows: If Interval W-Y : : : ; 2.5, Print Cycle W-A = 3. 75 seconds; and If Interval W-Y > 2.5, Print Cycle W-A < 12 seconds; These conditions set the time at which the reconfiguration signal 86 is to trigger. Performance is lost when the Top to Print interval W-Y exceeds 2.5

seconds, which in turn forces the reconfiguration signal 86 to slip by up to 12 seconds.

At step 106, the controller 26 attempts to adjust parameters that result in performance degradation to reduce the probability of future failures. The adjusted parameter is saved to the non-volatile memory 32 to replace the non-optimal value (step 108). This process can be iterative to reach an optimal value for the particular printer.

Suppose, for example, that in a particular printer, the time Z of the reconfiguration signal 86 occurs after the next top signal 80 at time A. This may occur, for instance, if the print cycle only runs for 3.6 seconds between consecutive top signals, rather than the specified 3.75 seconds. The reconfiguration signal 86, which is designed to trigger approximately 0.1 second before the next top signal, or 3.65 seconds after the last top signal, does not trigger in time for the printer to prepare for the next pass. In this case, the printer returns a"service error".

The controller detects this inaccuracy and determines that the parameter of 3.75 seconds that is suppose to reflect the top-to-top print cycle is actually off at least 0.15 second. As a result, the controller reduces the print cycle parameter by at least 0.15 second, or say perhaps 0.3 second, to tune the parameter. This places the print cycle parameter at 3.45 seconds, which is stored in memory in place of the default 3.75 seconds.

Now, when the printer runs through a subsequent print cycle at its adjusted 3.6 second duration, the reconfigure signal 86 is set to trigger 0.1 second before the print cycle parameter of 3.45 seconds, or at 3.35 seconds from the first top

signal. This allows sufficient time for the reconfigure signal 86 to trigger before the next top signal, thereby improving the performance of the printer.

The on-the-fly tuning advantageously brings the printer into optimal performance. The adjustments are made only at the expense of shortening the time at which the CPU is made available for non-printing tasks. In the last example, the reduction of the print cycle by 0.3 second effectively shaves 0.3 second from the resource free time, reducing it from 1.47 seconds to 1.07 seconds. Such a reduction has little impact on the controller's ability to compress the raster data in a timely manner for a subsequent plane.

Although the invention has been described in language specific to structural features and/or methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps are disclosed as preferred forms of implementing the claimed invention.

Claims

1. A method for operating a printer, comprising the following steps: establishing a set of operating parameters for operating the printer; monitoring the set of operating parameters to detect when one of the parameters is not in compliance; and adjusting the parameter detected to be non-compliant by an adjustment factor that brings the parameter back into compliance.

2. A method as recited in claim 1, wherein the set of operating parameters comprise an engine cycle time, a printing phase in which the controller facilitates printing during the engine cycle time, and a non-printing phase in which the controller performs other tasks besides printing during the engine cycle time.