WO2002014077A1 - Method and apparatus for ensuring output print quality - Google Patents

Abstract

Printed image output quality can be guaranteed by using an optical scanner (300) to read image output quality from a printer (200) in real time. In one embodiment, a registration mark (410, 412, 414, 416), preferably comprised of at least one pixel of each color of a multi color print head, printed in the margin (406, 408) can be optically scanned by a scanning device (216, 300) mounted along side the print element (214). In another embodiment, a complete image (504) can be scanned one line at a time pixel by pixel by the optical scanner as an image is painted by a print mechanism.

Description

METHOD AND APPARATUS FOR ENSURING OUTPUT PRINT QUALITY

FIELD OF THE INVENTION This invention relates to printers. In particular this invention relates to a method and apparatus for ensuring the output print quality from a printing mechanism.

BACKGROUND OF THE INVENTION Inkjet and laser printers are well known in the art. At least one problem with virtually all such printers is the inability to detect depleted inks in the case of ink j et printers and toner in the case of laser printers, the loss of which adversely affects print quality. Similarly, damaged or inoperative print heads, ink cartridges or laser printing mechanisms also adversely affect the output print quality. A paper (or other media) handling mechanism, can mis-feed or mis-direct the media, also affecting who the output might look, hi extreme cases, the undetected depletion of ink from an inkjet print cartridge or a clogged print nozzle can render a printed output useless.

A method and apparatus by which printed output from a print mechanism can be guaranteed would be an improvement by which output print quality could be more rigorously maintained.

SUMMARY OF THE INVENTION A method and apparatus for ensuring output print quality includes the printing and detection of a registration mark in one or more of the margins of an image to be printed. A registration mark is optically scanned to detect whether the print mechanism of the printer is in fact capable of depositing ink onto the print media and that the registration mark is correctly laid down (deposited onto the media). BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a simplified block diagram of an inkjet printer coupled to a personal computer which controls the printer and its output.

Figure 2 shows a simplified block diagram of the functional elements of an inkjet printer, such as that shown in Figure 1.

Figure 3 shows a side view of an optical scanning mechanism assembly. Figure 4 shows an exemplary layout of registration marks in the margins of a printed image.

Figure 5 shows an area of a printed page on which a printed image might be optically scanned as it is printed in accord with the embodiment disclosed herein.

Figure 6 shows an exemplary inkjet print cartridge, which may be employed in the present invention.

Figure 7 shows a flow chart depicting the process of ensuring print quality, which may be employed in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows a computer 100 electrically coupled to a printer 200 by means of an appropriate communications media such as infrared, radio frequency energy, or as shown in Figure 1, a cable 102. The printer 200, is preferably an inkjet printer such as one of those manufactured by the Hewlett-Packard Company but might also be a laser printer or other type of printer such as a piezo-electric based inkjet printer manufactured by other entities. As is known in the art, the printer 200 depends upon signals from a computer 100 in order to produce meaningful output onto a print medium 202, which might include paper, transparencies, envelopes, fabric, film, iron-on transfers or other printable medium.

The images that the printer 200 produces include graphics and alphanumeric characters. These images are electronically prepared, formatted, and transmitted to the printer 200 via the cable 102. Indeed, all of the printed output produced by the printer originates from signals from the computer 100. These signals cause the printer 200 to deposit ink or toner onto the print media 202 such that an image (graphics or alphanumeric characters) is printed on the media. As toner (in the case of a laser printer) or ink (in the case of an inkjet printer) is depleted, if the print mechanism fails, or if the print media is exhausted, the computer 100 is typically unaware that a print output problem exists. A method and apparatus by which the computer 100 or the printer 200 can be made immediately aware of print quality loss can reduce or eliminate wasted time or print media. If the printed output is tested as the output is produced, output print quality can be maintained.

Figure 2 shows a representative depiction of the working components of the printer 200 shown in Figure 1. In Figure 2, a piece of print media 202, which might include paper or transparency sheet, is urged by one or more rollers or platens 204 under the control and operation of a platen motor 206. The platen motor 206 rotates the platens or rollers 204 to move the print medium 202 under a translating (i.e. reciprocating) print head 208 that moves in two directions along an x axis under the control of a print head step or control motor 210.

A continuous drive belt 212, to which the print head 208 is attached, is rotated by the print head stepper motor 210. The movement of the drive belt 212 acts to position the print head 208 along the x axis such that ink or toner can be deposited onto the print medium 202 from one or more print heads 214 that include for example a thermal inkjet print head or piezo inkjet print head, well known to those skilled in the art.

Ensured output print quality is achieved in a preferred embodiment by using an optical scanner to read printed output (i.e. images formed from ink or toner). Electrical signals from the optical scanner are compared (by the computer 100 or by a processor within the printer) to signals from the computer 100 (and which representing what should have been printed) to determine whether the actual printed output is an accurate reproduction of what the computer sent to the printer. Whether the printer is printing graphics images (photographs, pictures, etc.) or alphanumeric characters (letters, numbers, typographic symbols, etc.), to the printer, all printed images are formed from individual dots or pixels. Ensuring the output print quality of any sort of image is achieved using the same process or optically scanning what was printed and comparing the scanned image to what the printer was instructed to do. With respect to the comparison of the scanned images and how the scanned images compare to what the printer was instructed to print, there will typically be a correlation or calibration of the scanner's signals to the signals sent from the printer because the nature of the output signals from the scanner will be different from the signals sent to the printer from a computer. The correlation of optical scanner signals to printer control signals will of course depend upon the nature of the scanning device as well as the nature of the control signals sent to the printer and will typically require processing of the scanner output signals or processing of the printer control signals.

Because the scanned image will rarely, if ever, identically match the image that a printer was instructed to print, as part of the comparison process, various user-definable differences between the scanned image and the intended image can be programmed into the processor performing the comparison in order to be able to increase printer yield and have a workable printer product.

In Figure 2, an optical scanner 216 is positioned along side the print head 214 (only one of which is shown) such that the scanner 216 is capable of optically scanning images that are printed by the print head 214. In alternate embodiments two or more multi-color print cartridges can be used wherein the scanner 216 would scan images produced by all of the cartridges.

Control signals to the print mechanism 208 are provided by a print head controller 218, which in the preferred embodiment interfaces the print head mechanism 208 including the scanner 218 and the print cartridge 214 to a printer controller 220. As such, the print mechanism controller 218 is used to control the print head cartridge 214 in order to print an image, while it controls the optical scanner 216 to read what was printed as the print head mechanism 208 is moved over the just-printed image.

As the optical scanner 216 scans images that are just printed, electrical signals it produces are fed back through the print head mechanism controller 218 to the printer controller 220, and in the preferred embodiment back to the computer 100 shown in Figure 1 via the cable 102. In an alternate embodiment, signals from the scanner might be processed in the controller 220 or other processor within the printer 200. If the signals from the scanner show that the printed output does not correspond to what was "printed" by the computer, further printing can be suspended until the cause of the output defect(s) is determined and corrected. A representative depiction of an optical scanner is shown in Figure 3 where print medium 302 has already been printed with an image or portion thereof. A light source, such as an LED (light emitting diode) 304, illuminates the medium 302 by light in either visible or invisible portion of the spectrum. Other light sources such as a broad-spectrum bulb (not shown), the light of which is conducted into the print mechanism via a fiber optic cable (not shown) could also be used. Light waves from the LED 304 exit from an orifice 306 in the optical scanner 300 and travel therefrom in all directions. At least some the light from the LED 300 is projected onto a portion of the print medium 304 where an image to be scanned is illuminated by the light waves 310 from the LED 304. Upon reflection from the print medium 302 surface, these light waves 310 are reflected 312 back through a collimating lens 314 in the optical scanner housing 316.

The first collimating lens 314 works with a three-hole collimator 318, 320 and 322 to collimate the reflected light 314 onto one or more photo diodes 324 from which electrical signals are generated representing the present or absence of an image immediately below the optical sensor 300.

Signal processing electrical signals from optical sensors in printers is disclosed in the literature including for example U.S. Patent No. 5,289,208 to Robert D. Haselby for an "Automatic Print Cartridge Alignment Sensor System" issued February 22, 1994 and assigned to Hewlett-Packard Company, the assignee hereof. Methods such as the one disclosed by Haselby could be used to determine where the print mechanism is or sees. Upon the detection or sensing of an image on the medium 302, by the optical scanner 300, the electrical signals generated by the photo diode can be appropriately processed using for example processes similar to that disclosed by Haselby to determine whether or not an image on the medium 302 is correctly printed or printed at all. The electrical signals from the optical scanner 300 can be processed either within the printer 200 or sent back to the originating computer 100 for evaluation.

In one embodiment of the invention, readily-detectable and processed registration marks are printed in the margins of an image either before and/or after each line of the image is printed by the print head mechanism. Figure 4 shows an exemplary sheet of paper 402 and the printable area 404 where an image or text is typically printed by a printer such as the one disclosed in Figure 1. The printed page 402 includes a printable area 404 along side of which are left and right hand margins 406 and 408 respectively. As one registration mark or line is printed in one margin, the print mechanism can either continue printing the same line or print a subsequent line as the platen moves the paper under the print mechanism. In either fashion, a registration mark is printed and scanned, either before or after a line of output is laid down.

As shown in Figure 4 a registration mark printed in either one or both of the margins 406 and 408 on every pass of the print head over the printed page will create vertical lines 410, 412, 414 and 416 corresponding to the cyan, magenta, yellow and black inks that are normally used in the most color printers. Stated alternatively, as the print mechanism shown in Figure 2 traverses across the medium 202 in the x direction, the medium is indexed under the control of the platen motor 206 to position a different portion of the print medium 202 under the print head mechanism 208. If the registration marks printed by the print head mechanism 208 are comprised of at least one pixel of each color the resultant output printed registration mark will be a series of vertical lines printed in the margins. In Figure 4, reference numerals 410, 412, 414 and 416 represent the individual colors that would be printed from a four color print head 208.

In an alternate embodiment, the optical sensor or optical scanner 216 can be used to continuously scan an image in a printed image area on a piece of print media.

Figure 5 shows an exemplary printed page 500 including an image area 502 where there is printed a series of pixels 504 that might comprise a portion of a graphical image. Similarly, the image might be comprised of alphanumeric characters 506 also as shown in Figure 5. As the print head 208 traverses the printed area of the image 502, the optical scanner 216 can read individual portions of either the individual pixels of an image 504 or the printed alphanumeric characters 506. The resultant electrical signals produced by the optical scanner 216 can be read back by a computer 220 within the printer 200 or sent back to the processing and controlling computer 100 for analysis. By reading spectral qualities of the registration marks or other images, such as hue, luminance, saturation and the like, over-all output quality can be truly maintained in real time. Still other embodiments of the invention would include using a fixed scanner that reads substantially the same portion of a printed medium. A fixed scanner similar to that shown in Figure 3 could be positioned to read the aforementioned registration marks. By fixedly mounting the scanner, or an array of such scanners, above one or both of the margins, registration marks in the margins could be read continuously. An array of such scanners could read an entire page width, or portion thereof, to continuously scan printed images like using a page wide area scanner. See U.S. Patent No. 5,532,825 issued to Lim, et al., and assigned to the Hewlett-Packard.

Figure 7 shows a flow chart 700 depicting the steps of the methods disclosed herein whereby output print quality is ensured. With respect to Figure 7, the printer (identified in Figure 1 by reference numeral 200) receives printer control codes and print data (i.e. print signals) 702 from the computer (identified in Figure 1 by reference numeral 100). The printer prints 704 either a registration mark or portions of an image to be printed in response to the print signals 702 sent to the printer.

After the registration mark (or image portion) is printed, the mark (or image portion) is optically scanned 706. Signals from the scan 708 are read into either the printer controller 218 or sent back to the computer 100 sending print signals to the printer 200 for analysis. Signals from the scan 708, which represent the image that was actually printed, are processed and compared 710 to the signals 702 that were sent to the printer such that a determination can be made whether the image that was actually printed is acceptable, i.e. is the output good enough? If the signals from the scan and the signals to the printer compare favorably, printing can continue 712, including any real-time adjustments to the printer output that might be needed as determined from the comparison 710. If the comparison of the printed image to the print signals shows that the output quality is poor, an error message or warning can be generated to the user or to the computer to inhibit further printing until the cause of the output quality failure is identified and corrected 714.

While the preferred embodiment of the invention contemplates using a photo diode sensor in the optical scanner, alternate embodiments would include using a charge coupled device, a magnetic sensor or other arrays of photo diodes. A preferred embodiment also contemplates that the personal computer 100 performs the functions of controlling the print head mechanism and reading output from the optical scanner, a separate processor 218 or 220 within the printer might also function to analyze electrical signals generated by the optical sensor 216. Neither one of these locations for a suitable processor to analyze data sent to the print head 208 from the computer as well as read back and interpret signals from the scanner might be used with equal results.

In a preferred embodiment, the registration mark(s) printed in the margins of an image preferably exercise all of the functions of a print mechanism. In Figure 6, an exemplary inkjet print cartridge 600, known to those skilled in the art, may have perhaps hundreds of individual ink energizing elements 602 in the inkjet print head 604. In the course of ensuring that the print cartridge 600 is fully functional, the registration marks printed on a document, preferably exercise each of the firing elements 602 of the print cartridge 600. In alternative embodiments, such as a laser printer, the registration mark might be chosen to ensure that a rotating drum member or the laser mechanism would be fully exercised in printing the registration mark. hi scanning the registration mark, as well as the images printed on a page, the optical scanner 218 is preferably capable of measuring color characteristics of the output print of the print mechanism. These color characteristics would of course include hue, luminants, saturation, as well as various noise components commonly found in output print images. Being able to determine the overall spectral qualities of the registration mark is useful to determine that the output of a graphics image such as a photograph comports with the signals that were sent to the printer from the computer. In one embodiment of the methodology, registration marks are printed before the print head begins to print an image which might be either in the left or right hand margin. In an alternate embodiment, the registration mark, by which the output is tested might be tested after the printer prints a portion of an image either on a line by line basis or character by character basis. While the invention disclosed herein finds application with a printer, it should be apparent that the invention would have found application with other devices including fax machines, thermal printers, laser printers, off-set printers, fabric printers, photoprinters and virtually any other kind of print output device. This invention also finds application in copiers as well. By using either a moveable scanner that scans images in individual, sufficiently closely-spaced lines, or by using an array of fixed scanners that can read an entire page, output print quality from a laser printer, fax machine, thermal printer, off-set printing press or from a copier, indeed any sort of print device, can be continuously ensured. Page-wide scanners are known in the art.

Upon the determination that either the registration mark or a portion of an images was successfully printed, or that the output image quality that is determined by the real time scanning process described above is successful, the printer can be inhibited from any further activity if the image is incorrect, or allowed to continue printing if the optical scanning detects that the output image quality is appropriate. The printing device might also undertake corrective actions, such as compensating for a depleted black ink by mixing cyan, magenta and yellow inks, which when combined closely approximates black. Similarly, the computer controlling the printer might adjust color or output print intensity so that the image that was actually printed more closely resembles the image that is represented by the electrical signals sent to the printer. On a color fax machine or printer, the fax or printer might stop printing in color and instead print in gray scale.

We claim:

Claims

1. A method of ensuring print quality of a printed image comprised of the steps of: printing at least a portion of an image on a medium in response to a first set of image print signals (704); scanning the printed portion of said image (706) on said medium by a scanner, thereby producing a second set of signals (708) representing the image that was printed on said medium; comparing said first set of signals to said second set of signals (710); enabling said printer to print said image upon the determination that said portion of the image was properly printed (712).

2. The method of claim 1 wherein said step of enabling said printer to print said image is comprised of the steps of adjusting printer output (712) such that the image substantially matches the image represented by said image print signals.

3. The method of claim 1 wherein said step of scanning the portion of an image on said medium is further comprised of the steps of: optically scanning the portion and reading output signals (708) from an electronic image scanner (218, 300) coupled to said print mechanism (208) electronically scanning images printed onto said medium (202) by said print mechanism (208).

4. The method of claim 1 wherein said step of scanning the portion of an image (706) is comprised of the step of optically scanning at least portions of a printed page (202) using a fixed optical scanner.

5. The method of claim 1 wherein said step of optically scanning a portion of the image is comprised of the step of scanning using a page wide array scanning mechanism 300.

6. The method of claim 1 wherein said step of enably said printer to print said image is comprised of the steps of adjusting the printer output.

7. An apparatus for monitoring output print quality of a printed image, said apparatus comprised of: a print mechanism (208) coupled to a print mechanism position controller (218); a scanner (216) operatively coupled to said print mechanism (208); a controller 9220) having an input for receiving printing control signals from a computer (100), an input for receiving signals from said scanner (216) and an output coupled to said print mechanism position controller (218), said controller comparing: signals received from a computer defining an image (504) to be printed to signals from said scanner representing an image that was actually printed.

8. An apparatus in accordance with claim 7 further comprising: said print mechanism including a moveable inkjet print head having a pluraity of printingt elements (602), each printing element being capable of depositing ink drops on a print medium (20) so as to produce an image (504) on said print medium; and an ink reservoir (600), operatively coupled to said plurality of printing elements (602) and providing ink thereto, whereby said scanner substantially continuously scans ink drops deposied onto a predetermined portion of said print media under the control of said controller.