AU713308B2

AU713308B2 - Process for the control of characters printed by a printer and apparatus for performing said process

Info

Publication number: AU713308B2
Application number: AU70648/96A
Authority: AU
Inventors: Laurent Farlotti; Jannick Michallon
Original assignee: Imaje SA
Current assignee: Markem Imaje SAS
Priority date: 1995-11-08
Filing date: 1996-11-04
Publication date: 1999-11-25
Anticipated expiration: 2016-11-04
Also published as: JPH09174825A; FR2740729B1; EP0773513A1; CA2189730A1; FR2740729A1; AU7064896A

Description

1

AUSTRALIA

Patents Act 1990 IMAJE S.A.

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT *r Invention Title: Process for the control of characters printed by a printer and apparatus for performing said process The following statement is a full description of this invention including the best method of performing it known to us:- 0 I

DESCRIPTION

TECHNICAL FIELD The invention relates to a process for the checking and control of characters printed by a printer, particularly an ink jet printer, and to an apparatus for performing said process in an industrial printing installation.

PRIOR ART Ink jet printer applications are regularly increasing in the field of industrial marking. In a purely illustrative manner reference can be made to the printing of freshness dates or batch numbers on agro-alimentary products. The satisfactory operation of these printers is governed by a certain number of parameters, which must be perfectly controlled if it is wished to obtain an excellent printing quality. Despite numerous improvements introduced over the past few years to such printers, they still suffer from a drift of random parameters governing their operation and may lead to-a deterioration in the printing quality. In most cases, this deterioration has a typology related to the defective parameter. For 25 example, the absence of an impact of drops on the support to be printed can mean that the head requires cleaning. In the same way a positioning deficiency with respect to the drops can correspond to an abnormal drop :ejection speed, an incorrect printing distance, or an incorrect speed of the relative displacement of the head and the object to be printed. Other 30 defects are imputable to the means for conveying the object to be printed, namely sliding, vibrations, collisions, etc. As production or conditioning lines are increasingly being automated, the permanence of the printing quality is vital. The marking function very frequently occurs at the end of the production line, so that any defective marking leads to unacceptable losses.

FR-A-87 16 446 describes a process for controlling the printing quality of an ink jet printer, in which the printer prints at periodic intervals a 2 specific control frame. This frame is read by an associated sensor and compared with a reference frame. This frame is chosen to be representative of the characters which are most difficult to print. The exploitation of the results makes it possible to check that the printing of the control frame is correct or alerts an operator in the case of drift or shift.

However, this process is unsatisfactory, because it does not permit the checking of the marking conformity. There is an increasing need for checking the printed message, no matter whether this is under the increasing pressure of regulations imposing a correct and legible marking, or the wishes of the manufacturer to minimize risks of an incorrect interpretation of the message, or quite simply guarantee the conformity with internal or external graphic standards.

Vision systems making it possible to control or check a printed message have been proposed. Certain systems use sensors and image processing algorithms able to give information on the quality of the message following a learning phase, e.g. by comparing the position and contrast of an image with those of a reference image. These systems suffer from the disadvantage of requiring a new learning phase whenever the content of the message 20 and therefore the corresponding printed image varies to a significant S. extent.

Other more sophisticated systems are able to recognize each character of a printed message in the fonts or sets of characters known beforehand. However, these systems require the prior learning of printed images in a correct manner and a significant storage capacity for retaining all the correct reference images.

To obviate the various disadvantages of the prior art means, the present 30 invention relates to a process for controlling and checking printed characters and an apparatus for performing said process able to continuously **CU check and control the conformity of the printed messages.

DESCRIPTION OF THE INVENTION The present invention relates to a process for controlling the quality and 3 checking the conformity of the printing of a printer, which can be an ink jet printer, on at least one moving object, characterized in that it comprises the following stages: printing on each moving object at least one image, continuous transmission of a description of each printed message, construction of a reference image of said printed message, recording a real image of the printed message, comparison of the real image with the reference image, continuous transmission of the result of the comparison, decision concerning possible remedial actions as a function of said result.

The comparison between the real image of a printed message and the reference image supplies information on the parameters governing the printing quality, so as to permit decisions concerning remedial actions.

o00o Advantageously, the recording of the real image of the printed message takes place after a delay calculated as a function of the printing time or reception time of a sync signal supplied by the printer, or the reception time of a signal supplied by an appropriate sensor, or on the basis of a continuous analysis of the real image of the printed object or objects, if certain previously determined conditions are fulfilled.

Advantageously, the printer prints messages in binary graphic or bitmap form.

The process according to the invention consists of: closely associating a printer and a control system, ses*.* continuously transmitting by the printer of a description of the printed message, constructing a reference image of the message on the basis of the description, recording the real image of the printed message at the appropriate time, comparing the recorded real image with the reference image, immediately supplying a result of said comparison.

The invention also relates to an industrial marking installation, which comprises: a moving conveyor which receives at least one object to be marked; a printer with its printing head for printing at least one message on each object; a detection cell for detecting the presence of at least one object on the conveyor, and a tachymetric encoder for measuring the conveyor speed, both being connected to an industrial interface of the printer; a camera which is situated downstream of the printing head; a control system which comprises means for processing and comparing the image printed by the printing head on each object and recorded by the camera, and the reference image constructed from the description of the 0 printed message, the printer and the camera being connected to said control Sgsystem; and wherein the printer and the control system form an integrated system :15 from the hardware and software standpoint in order to reduce information 0. transmission and processing delays.

**...Advantageously, the checking and control system is constituted by an image processing card or vision card of a sensor or camera, as well as a monitor used in the installation and debugging phases of the system, so as to establish optimum illumination conditions for recording printed messages.

This control system can also be used for controlling conditions during manufacture.

oo The apparatus of the invention can be supplemented by a terminal associated with the printer, which in particular serves to edit messages, carry out maintenance operations and enter the initial parameters of the printer and the control system.

One of the advantages of the invention is that each message can be represented in binary form and that the corresponding reference image can be reconstructed by the control system. Thus, there is no longer a need to carry out beforehand a learning of said reference image. Moreover, the message to be printed can vary between individual objects in a continuous manner, to the extent that the transmission and processing electronics have adequate performance characteristics to take account of these variations. In addition, as the binary form is used for describing the characters in the internal procedures of the printer, the description of the messages to be controlled can be transmitted a very short time after printing.

4a Another advantage of the invention is that a minimum space is maintained between the printing location and the checking location, which makes it possible to minimize the number of messages taking place, i.e.

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OS S S 50 S SS 5 printed and not yet controlled. The storage capacity necessary for containing these messages can be decreased as a function thereof.

The invention applies to any industrial marking installation using the ink jet procedure, but can also apply to other printing methods, to the extent that the printed message can be described in binary graphic form.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 diagrammatically illustrates the apparatus for performing the process according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS In the case of an industrial marking installation as shown in fig. 1, a printer 10 deposits by means of its printing head 11 a marking on objects 12, 13 displaced by a conveyor 14 (displacement direction 18). A detection cell 15 and a tachymetric encoder 16 connected to an industrial interface 17 of the printer 10 respectively supply informations on the presence of 20 objects to be printed and on the conveyor speed. These informations make it possible to initiate printing at a time such that the marking is correctly positioned on each object.

9 99*9 These informations can also be used by a checking and control system, e.g.

constituted by an image processing card or vision card 20, a sensor or camera 21 and a monitor 22. The monitor 22 is used in the system installation and debugging phases for establishing optimum illumination conditions for the recording of printed messages. It can also be used for controlling conditions during manufacture. In the present example, the installation is completed by an input-output terminal 23 associated with the printer The terminal 23 is used for editing messages, carrying out maintenance operations and entering the initial parameters of the printer and the control system.

When the cell 15 detects an object 12 or 13 to be printed, it emits a signal Dtop intended for the printer 10, which can also receive an information Tachy 6 of the speed of the conveyor 14 supplied by the tachymetric encoder 16.

Printing takes place at the instant when the object to be printed passes beneath the head 11. The printer 10 then supplies to said vision card 20 a description of the printed message. The vision card 20 constructs a reference image from said description. Following a signal from the printer and whilst taking account of the distance between the head 11 and the camera 21 and the speed of the conveyor 14, the camera 21 records the image actually printed. This image is compared with the reference image by the vision card 20. The result of this comparison is transmitted to the printer. As a function of this result, the printer transmits an information to the operator via the terminal 11 or to a not shown, external supervision system via its industrial interface 17.

In another embodiment, recording is initiated by a second, not shown, detec- 15 tion cell. The displacement of the recording can also occur as from a continuous analysis of the image of the conveyor 14, if certain predetermined conditions are fulfilled, e.g. the appearance of an object in the field of the camera 21.

20 When the speed of the conveyor 14 is considered as being fixed, it can be entered into the printer via the terminal 11. In this case, the tachymetric encoder 16 is not used and the printer generates the necessary sync signals.

In the case where the marking is deposited on a single and not several moving 25 objects, the printer 10 generates the useful sync signals for printing and checking.

According to a feature of the invention, the printed message is in binary graphic or raster or bitmap form. In this form, the message is considered as a horizontal succession of vertical frames having points to be printed or empty spaces. Each frame can be represented by a succession of bits equal to one for a point to be printed and to zero for an empty space.

This representation is very suitable for ink jet printed messages, to the extent that each point will also correspond with one or more ink drops. Each character consequently has a representation in binary form used in the 7 internal procedures of the printer. Thus, the message to be printed can be transmitted to the control system and is taken into account in a very short delay following the printing.

According to another feature of the invention, the control system is able to measure variations between the theoretical position of the points in the reference image and the real position of the points in the printed image and is also able to detect the absence of points. These variations give informations on possible drifts to parameters governing the printing, as described in FR-A-87 16 446.

As a function of the variations found between the printed image and the reference image, the control system can emit signals intended for the printer or an external supervision system which, according to the particular case, 15 can take different decisions. They can e.g. consist of alerting an operator in the case of a drift requiring a maintenance operation, updates statistics concerning the quality of the printing obtained and free an object from incorrect or illegible marking.

20 In order to reduce information transmission and processing delays and minimize the production costs of the assembly, the printer and the control system can be associated from the hardware and software standpoint, so as to give an integrated system.

Claims

1. Process for the checking and control of characters printed by a printer on at least one moving object, characterized in that it comprises the following stages: printing on each moving object at least one message, continuous transmission of a description of each printed message, construction of a reference image of said printed message, recording of the real image of the printed message, comparison of the real image with the reference image, continuous transmission of the result of the comparison, decision concerning possible remedial actions as a function of said result. 5

2. Process according to claim 1, characterized in that the recording of the *real image of the printed message takes place after a given delay.

3. Process according to claim 2, characterized in that the delay is calcu- lated as a function of the printing time.

4. Process according to claim 2, characterized in that the delay is calcu- lated on receiving a sync signal supplied by the printer.

5. Process according to claim 2, characterized in that the delay is calcu- -lated on receiving a signal supplied by an appropriate sensor.

6. Process according to claim 2, characterized in that the delay is calcu- lated on the basis of a continuous analysis of the real image of the printed object or objects, if certain predetermined conditions are fulfilled.

7. Process according to any one of the preceding claims, characterized in that the messages are printed in binary graphic form.

8. Process according to any one of the claims I to 7, characterized in that the comparison between the real image of a printed message and the reference image supplies informations on the parameters governing the printing quality, so as to permit a decision on possible remedial actions.

9. Process according to any one of the claims 1 to 8, characterized in that the printer is an ink jet printer.

Industrial marking installation which comprises: a moving conveyor which receives at least one object to be marked; a printer with its printing head for printing at least one message on each object; a detection cell for detecting the presence of at least one object on the conveyor, and a tachymetric encoder for measuring the conveyor speed, both being connected to an industrial interface of the printer; camera which is situated downstream of the printing head; 15 a control system which comprises means for processing and comparing the image printed by the printing head on each object and recorded by the camera, and the reference image constructed from the description of the printed message, the printer and the camera being connected to said control system; and wherein the printer and the control system form an integrated system S from the hardware and software standpoint in order to reduce information transmission and processing delays. 0

11. Process for the checking and control of characters printed by a printer •25 on at least one moving object substantially as described herein with reference to the accompanying drawings.

12. Industrial marking installation substantially as described herein with reference to the accompanying drawings. Dated this twenty-fourth day of September 1999 IMAJE S.A. Patent Attorneys for the Applicant: F B RICE CO