GB2325438A

GB2325438A - An ink jet printing method involving analysis of individual printing elements of a printhead and production of a modified printhead control signal

Info

Publication number: GB2325438A
Application number: GB9710373A
Authority: GB
Inventors: Steven John Buckby
Original assignee: Markem Technologies Ltd
Current assignee: Markem Imaje Industries Ltd
Priority date: 1997-05-21
Filing date: 1997-05-21
Publication date: 1998-11-25
Anticipated expiration: 2017-05-21
Also published as: GB9710373D0; DE69814518T3; DE69814518D1; EP0879699B2; EP0879699A2; EP0879699B1; US6290316B1; EP0879699A3; DE69814518T2; GB2325438B

Abstract

The method comprises analysing the performance of individually actuated printing elements (12,Fig. 1) of a printhead 11 to determine a printing characteristic of the printhead such as the ink jet velocity or the amount of ink emitted in an ink jet and to produce control data, feeding the data to a controller 14 which uses it to compensate for variations in the performance of the printing elements whereby the controller produces modified control signals for the printing elements so as to adjust the printing characteristic of the printhead. A test print 22 may be produced and electronically examined by a camera 30 to produce a control data input to the controller. The method may also be applied to a thermal transfer printer.

Description

2325438 PATENTS ACT 1977 DJL/A910OGB Title: Method of Printing This

invention relates to a method of printing and more particularly to a method of printing utilising a print head of the so called ink jet kind, t) 0 although the invention may be applied to a method of printing having other kinds cl of print head comprising a plurality of printing elements which may be actuated independently to print on a substrate.

In one kind of ink jet printer, there is provided an array of printing elements e.g. arranged in a linear or substantially linear array, and each of which 0 0 1 may create a jet of ink and propel the ink towards a substrate. The jets may be created by, for example, passages in the print head which are caused to constrict 0 by piezzo electric means, to squeeze ink therefrom or by other similar means.

1 The design and manufacturing tolerances of such print heads is 0 1:1 demanding and it will be appreciated by those skilled in the art, that the 1 performance of the individual printing elements will in practice vary, such that 0 print heads tend to be imperfect. This variation in performance of the printing Z elements leads to print image irregularities. Where the variation in performance 0 0 of the individual printing elements is too great, the print head has to be rejected.

cl c The variation in performance may mean that the amount of ink and/or the velocity of the ink in the created jet is not constant for all of the printing elements. The latter of these produces the result that the ink in one or more jets reaches the substrate at a different tirne to ink from others of the jets, even where the jets travel substantially the same distance from the print head to the substrate. In general, in a printer of this kind, during printing there is relative movement between the substrate and the print head, and consequently, the qLialit'y..of the image is impaired by an aniount proportional to the velocity variation.

According to a first aspect of the invention we provide a method of C printing utilising a print head comprising a plurality of printing elements which C1 c Z:> 1:1 may be aCtUatCd independently to print on a SUbstrate, and a control means which 2 produces control signals for the printing elements for independently addressing and controlling the printing elements so that the print head may print a desired character, characterised in that the method comprises analysing the performance of the individual printing elements to determine the printing characteristic of the print head and to produce control data, feeding the control data to the control means which utilises the control data to compensate for variations in the performance of the individual printing elements whereby the control means produces modified control signals for the printing elements so as to adjust the 0 printing characteristic of the print head.

0 The control means may use the control data to compensate for variation in performance of the printing elements by one of actuating one or more of the printing elements at a different tin-le to others of the printing elements to ensure, in an ink jet type printer as. described above, so that the ink from all of the jets reaches the substrate at the same time. Alternatively or additionally, the control means may use the control data to compensate for variation in performance of the printing elements b providing a control signal to c y 1 C one or more of the printing elements at a power different to others of the printing CY elements.

In each case, the variation in performance of the printing elements is compensated for with so that the quality of the resultant image is improved.

c The characteristic of the print head may be determined at least in part by causing the print head to print a test print, and electronically examining the test print to produce a control data input to the control means but other analysing steps may be carried out for a particular kind of print head.

Where the printing elements each comprise nieziii,, to create a jet of ink and to propel the ink to the substrate, the characteristic of tile print head may be determined, at least in part by measuring for each printing element, the velocity of ink drops in the ink jet created thereby to produce the control data, using for example an electronic imaginu rneans which provicles a control data 0 C c input to the control means.

3 According to a second aspect of the invention we provide a printing 1 apparatus comprising a print head comprising a plurality of printing elements which may be aCtUatCd independently to print on a SUbStrate, and a control means which produces control signals for the printing elements for independently r 0 addressing and controlling the printing elements so that the print head may print a desired character, characterised in that means are provided for analysing the C performance of the individual printing elements to determine the printing characteristic of the print head and to produce control data, means to feed the control data to the control means which UtiliSCS the control data to compensate for variations in the performance of the individual printing elements whereby the control means produces modified control signals for the printing elements so as to adjust the printing characteristic of the print head.

The apparatus may have a print head of the kind in which the printing elements each comprise means to create a jet of ink and to propel the ink to the substrate and the means which analyses the performance of the individual printing elements, mea.SUres for each printing element, the velocity of Ink drops in the ink C jet created thereby to prodUCC the control data, U.Sling an electronic limagin. means which provides a control data input to the control means.

The invention will now be described with the aid of the accompanying drawings in which:- FIGURE 1 is an illustrative perspective view of a print head for use in the method of the invention; FIGURE 2 is an illustrative enlarged cross sectional view tliroLiyh the print head of figure 1; FIGURE 3 is an illustrative diagram of a printing apparatus embodying the invention.

Referrins! to the drawings, a printing apparatus 10 comprises a print W W 1:5 head 11 of the so called ink jet kind, having,t plurality of printing elements 12 arranged in t linear or substantially linear array, and each adapted, under the control of a control me.,in,, 14, independently from each other to propel the ink 4 towards a substrate 15.

For example, the print head I I may be of the PZT type having a Plurality of strips 17 of material which exhibit piezzo electric properties and move resiliently when an electrical signal is provided thereto, and a layer 18 of more rigid material attached thereto, there being a passage 19 between each piezzo electric strip 17 and the more rigid layer 18.

Ink is fed to each of the passages 19 under slight pressure, and when 0 4-) an electrical signal is provided to a piezzo electric strip 17, the strip 17 deforms to cause a jet of ink to be generated at a jet Outlet orifice 20 from the associated passage 9 and to be propelled therefrom.

C, There are several different print head designs relating to this technology and further detailed description of the design of the print head 11 is not considered necessary. However, as seen In figure 2, each passage 19 may include a constriction 21 to help develop the jet of ink, and typically, an electrical signal of about 200V is applied to the strip 17 of piezzo electric material. In practice, the print head I I may comprise I Substantial number of printing elements 12, e.g. 256 such elements 12, each element 12 being individuall

01 y controllable by a computer controlled control means 14, and to this end the print head I I may have a MLI]ti-circuit connector 26 to enable an electrical connection to be made with the piezzo electric strips 17 of each of the individual printing elements 12. Each printing element 12 will, when actuated, thus produce a jet of ink at the Outlet orifice 20 thereof.

In use, the print head 11 may be moved relative to a stationary substrate 15 such as a piece of paper, or an item of packaging, or the substrate 15 may be moved relative to I stationary print head 11, again Linder the control 0 of the control means 14, with the array of printing elements 12 being arranged transversely to the substrate 15, whilst individual printing elements 12 are actuated so as to print one or more desired characters on tile substrate 15.

Each jet of ink created by each printing element 12 will comprise a Plurality of individual drops of ink. Convent iona I ly, a selected number of the printing elements 12 are actuated Simultaneously by the control means 14 to produce a plurality of pixels of ink across the Substrate 15 at each pixel position along the substrate 15. Even though the distance the droplets of ink need to travel 1:1 4D from the print head I I to the Substrate 15 may be the same for al I of the actuated printing elements 12, because of manufacturing tolerances in the sizes of the passages 19 and of the Outlet orifices 20 thereof the performance of the printing elements 12, i.e. the amount of ink in any jet created, and the velocity of the ink in the jet, may vary compared to other.,; of the printing elements I? 0 To compensate for this, the control means, 14 in the arrangement of the invention, Litilises control data fed thereto, to produce modified control signals for the printing elements 12 so as to adjust the printing characteristic of the print I ZD head 11. For example, the control data may indicate that the velocity of the ink in a jet from one or more of the printing elements 12 is slower than for one or more of the remaining printing elements 12 and thus may compensate for this by providing the electrical signal or signals to the or each respective, slower, printing 0 ZD 0 element 12, earlier than to the or the remainder of the printing elements 12, at each pixel position along the substrate 15, so that the in]< frorn all of the actuated printing, elements impinges upon the substrate 1-5 at the sarne time. In this way C 0 1 the quality of the image which is printed on tile Substrate 15 is improved.

The control data may be derived frorn in analysis of the performance of the print head 11 for example by inspecting a test print 22 and/or by measuring ink droplet speed for each jet created by the printing elements 12 Preferably Such analysis is performed USinv an electronic iniaginu means, such as a camera 10 which prOdUCeS digital data which may be fed to the control means 14 as an ilIPLIt.

The control data may be stored, for example in a look Lip table 31, and may be used by the control means 14 when determining when to actuate the printing elements 12 of the print head 11, during the printing operation.

Various modifications may be Made Without departing from the scope of the invention.

6 For example as indicated above, the invention may be applied to in jet type printing apparatus in which jets of ink are produced by the printing elements C 0 12 otherwise than as described, or the invention may be applied to another kind of printer altogether such as a thermal transfer type of printer where the 1 performance of individual printing elements may vary. Thus the invention 0 encompasses not only actuating one or more printing elements at different times 0 to others of the printing elements, but also varying the power of the electrical 0 0 signal applied to one or more of the printing elements, e.g. to ensure more t> uniformity of printing by each of the printing elements.

0 In the example described, the control means '14 is illustrated as being separate from but electrically connected to the print head 12, but in another arrangement, the print head 11 may have part of the control means provided C - integrally therewith. For example, the look up table or other sore for the control data, when derived from an analysis of the printing characteristic of the print head C 11, may be provided in or on the print head 11.

The features disclosed in the foregoing description, or the following t> 0 0 claims, or the accompanying drawings, expressed in their specific forms or in C terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any ly combination of such features, he utilised for realising the invention in diverse forms thereof.

7

Claims

1 A method of printing utilising a print head comprising a plurality of C1 printing elements which may be actuated independently to print on a SUbstrate, and a control means which produces control signals for the printing elements for 4 independently addressing and controlling tile printing elements so that the print head may print a desired character, characterised in that the method comprises analysing the performance of the individual printing elements to determine the C7 C5 printing characteristic of the print head and to produce control data, feeding the 0 control data to the control means which utilises the control data to compensate for variations in the performance of the individual printing elements whereby the control means produces modified control signal,, for the printing elements so as to adjust the printing characteristic of the print head.

c A method of printing according to claim 1 characterised in that the Z7 c control means compensates for variation in performance of the printing elements by at least one of actuating one or more of the printing elements at a different time to others of the printing element....,, and providing a control signal to one or c 0 more of the printing elements at a power different to others of the printing elements.

A method of printing according to claim 1 or claim 2 characterised C, 0 in that the characteristic of the print head is determined at least in part by causing the print head to print a test print, and electronically, examining the test print to produce a control data input to the control iiieiii.

4. A method of printing according to any one of the preceding claims characterised in that the print head is of the kind in which the printing elements 0 are arranged in a linear or substantially I 0.inear array.

8 5. A method of printing according to any one of the preceding claims C1 characterised in that the print head is of the kind in which the printing elements 0 each comprise means to create a jet of ink and to propei the ink to the substrate.

6. A method of printing according to clairn 5 characterised in that the C1 0 characteristic of the print head is determined at least in part by measuring for each printing element, the velocity of ink drops in the ink jet created thereby to C produce the control data.

7. A method of printing according to clairn 6 characterised in that the 0 1:1 velocities of the ink drops in the ink jets created by the printing elements are determined utilising an electronic imaging means which provides a control data input to the control means.

A method of printing according to any one of the preceding claims I Z characterised in that the Method includes the step of rnoving the substrate relative to the print head during printing Cl 9. A method of printing substantially as hereinbefore described with reference to the accompanying drawings.

10. A printing apparatus cornprising a print head coniprising a plurality of c ll_n 1:1 printing elernents which rnay be actuated independently to print on a substrate, 0 1 and a control rneans which produces control signals for the printing elements for independently addressing and controlling the printing elements so that the print c C- C head may print a desired character, characterised in that rneans are provided for analysing the performance of the individual printing elements to determine the C printing characteristic of the print head and to produce control data, means to C1 feed the control data to the control rneans which wilises the control data to compensate for variations in the performance of the in(ii\'i(ILIZII printing elements 9 whereby the control means produces modified control signals for the printing elements so as to adjust the printing characteristic of the print head.

0 11. A printing apparatus according to claim 10 characterised in that the CI print head is of the kind in which the printing elements each comprise means to z create a jet of ink and to propel the ink to the SUbstrate and the means which analyses the performance of the individual printing elements, measures for each printing element, the velocity of ink drops in the ink jet created thereby to produce the control data.

12. A printing apparatus according to claim 11 characterised in that the 0 CI means which measures the velocities of the ink drops in the ink jets created by the printing elements comprises an electronic imaging means which provides a W 0 Z21 control data input to the control mean,.,.

1 1.

A printing apparatus substantially as hereinbefore described with 1 1 reference to and as shown in the accompanying drawings.

D CY 14. Any novel feature or novel combination of features disclosed herein or shown in the accompanying drawings.

W C