WO1999017102A1

WO1999017102A1 - A method of and apparatus for inspecting printed information

Info

Publication number: WO1999017102A1
Application number: PCT/SG1997/000049
Authority: WO
Inventors: Eng Chuan Toh
Original assignee: Siemens Aktiengesellschaft
Priority date: 1997-09-30
Filing date: 1997-09-30
Publication date: 1999-04-08
Also published as: AU4975497A

Abstract

An inspection system for inspecting information printed on a surface (3) of an electronic device (1) includes an image capturing device (5) for capturing an image of the information printed on the surface (3). The image capturing device (5) is coupled to a processing unit (12) and the processing unit (12) receives an input image from the image capturing device (5). The processing unit (12) is also coupled to a memory device (14) and an indicating device (11). The memory device (14) stores a template from which the information was originally printed on the surface (3). The processing unit (12) compares the capture image with a template retrieved from the memory device (14) and the processing unit sends a signal to an indicating device if the information printed on the surface (3) is not within a predefined deviation from the template and the indicating device (11), in response to the signal, indicates to a user that the information (4) printed on the surface (3) is outside the predefined deviation.

Description

A METHOD OF AND APPARATUS FOR INSPECTING PRINTED INFORMATION

The invention relates to apparatus for and a method of inspecting printed information and, in particular, for inspecting information printed on the surface of an electronic device .

It is common practice to print characters on the surface of an electronic device to enable the manufacturer of the device and the particular type of device and batch number to be identified. Generally, the information is printed on an external surface of a moulding which encapsulates the device. One of the more advanced methods of printing uses a laser marker which is controlled by a processing unit which instructs the laser marker to print the information in accordance with a pre-determined template.

After printing the information, it is necessary to inspect the printed information to ensure that it is legible and that it meets a minimum quality standard. Currently, an operator manually selects, from a batch of identical devices, a reference device on which the printing of the characters is of a high quality. The operator mounts the reference device on an inspection system which reads and memorises the printed information on the reference device. The operator then passes the remainder of the batch through the inspection system and the inspection system compares the quality of the printing of the information on each device with the quality of the printed information on the reference device stored in the memory. The inspection system then rejects devices on which the printing is of a standard which is below an acceptable deviation from the reference device.

A problem with this existing system is that the quality of the printing on the devices which are accepted or rejected by the inspection system is directly dependant on the quality of printing on the reference device selected by the operator. In- addition, with this existing system, a relatively high percentage of devices are rejected on which the printing on the device is in fact good. This percentage may be as high as, or in excess of, 10%.

In accordance with a first aspect of the present invention, a method of inspecting information printed on a surface comprises capturing an image of the information printed on the surface and comparing the captured image with a reference template from which the information was printed on the surface.

In accordance with a second aspect of the present invention, apparatus for inspecting information printed on a surface comprises an image capturing device for capturing an image of the information printed on the surface; a processing unit coupled to the image capturing device and receiving an input image from the image capturing device; a memory device coupled to the processing unit, the memory device storing a template from which the information was printed on the surface; and an indicating device coupled to the processing unit; the processing unit comparing the captured image with the template and the processing unit sending a signal to the indicating device if the information printed on the surface is not within a pre-defined deviation from the template and the indicating device, in response to the signal, indicating to a user that the information printed on the surface is outside the predefined deviation.

An advantage of the invention is that by comparing the information printed on the surface with the template from which the information was originally printed, the invention provides a more consistent method of inspecting information printed on the surface than by using a reference device.

Typically, the information printed on the surface comprises characters, such as alpha-numeric characters. In addition, or alternatively, the information may comprise a graphics image and/or a machine readable code, such as a bar code.

Preferably, the surface on which the characters are printed is the surface of an electronic device and preferably, the surface of the encapsulation of the device. Typically, the characters are printed using a laser marker controlled by a processing unit which uses the template to determine the characters to be printed on the surface of the device.

Preferably, the apparatus further comprises a reading device which reads a machine-readable code associated with the surface and selects an appropriate template from a number of templates, the template selected corresponding to the template from which the characters on the surface were printed. The processing unit may select the template from a remote database or from a memory device adjacent the processing unit. Typically, the processing unit forms part of a computer and the memory device may also be located in the computer. The machine readable code may form a portion of the printed information on the surface. Alternatively, the machine readable code may be on a separate surface, such as an information sheet associated with the surface. For example, where there are a number of identical surfaces, such as a batch of encapsulated electronic devices, the information sheet may be the batch (or lot) sheet.

Preferably, the reading device may comprise a bar code reader which reads a bar code associated with the surface. For example, the bar code may be on an information sheet.

In one example of the invention, the image capturing device may comprise an analog camera which is coupled to an analog to digital converter, the output of which is coupled to the processing unit. In alternative example of the invention, it is possible that the image capturing device may comprise a digital camera coupled to the processing unit.

Preferably, the indicating device may comprise a visual and/or audible indicating device. Preferably, the indicating device may comprise a visual display unit.

Preferably, an input device is coupled to the processing unit to permit an operator to input instructions to the processing unit. Typically, the input device may comprise a keyboard and/or a trackball .

Preferably, the method also comprises the step of optically character reading the characters printed on the surface and comparing the individual characters read by the optical character reader with the characters in the template.

An example of a method of and apparatus for inspecting information printed on a surface will now be described with reference to the accompanying drawings, in which :-

Fig 1 shows an electronic device on which alpha-numeric characters are printed;

Fig 2 is a schematic diagram showing a conventional inspection system; and,

Fig 3 is a block diagram showing an inspection system in accordance with the invention.

Fig 1 shows an electronic device 1 which includes a moulded encapsulation with a surface 3 on which information 4 in the form of alpha-numeric characters is printed. However, it is possible that the information 4 may comprise a graphics image, such as a company logo or other device type trade mark, and/or a machine readable code, such as a bar code, in addition to or as an alternative to the alpha-numeric characters .

Typically, the information 4 is printed on the surface 3 using a laser marker which is controlled by a processing unit. The processing unit instructs the laser marker to print the information 4 on the surface 3 in accordance with a template already stored in a memory device in a computer in which the processing unit is located. Alternatively, the template may be retrieved from a remote database or other memory device. The information 4 printed on the surface 3 includes the name of the manufacturer, the type or model of the electronic device 1 and other relevant information, such as the date of manufacture and a batch reference number.

During manufacturing, a large number of identical devices 1 are manufactured simultaneously and printed with identical information. After printing, it is necessary to ensure that the quality of the information 4 is sufficiently good to permit the information 4 to be legible and also that the information 4 printed is accurate and correctly identifies the device 1 on which it is printed.

Therefore, it is common practice to pass each device through an inspection system which inspects the information printed on the surface 3 to ensure that it is legible and the content is accurate.

A schematic diagram of a conventional inspection system is shown in Fig 2. The conventional system includes a camera 5 which is connected to a computer 6 via a cable 7. The camera 5 is attached to a lens 8 which focuses an image of the surface 3 when the device 1 is located below the camera 5 and lens 8. As described above, an operator selects a device on which the printed information 4 is of a high quality. The selected device is known as the "reference device" . The operator mounts the reference device on the inspection system and instructs the computer 6 (via a keyboard 9 and/or a trackball 10) to read and store an image of the surface 3 of the reference device within a memory device (not shown) in the computer 6. Information relating to the inspection process can be displayed by the computer 6 on a monitor (or VDU) 11.

After the image of the reference device has been stored, the operator passes each device in the batch under the lens 8 and camera 5. The inspection system compares the image of the information 4 on each device 1 in the batch with the stored information from the reference device. If the print quality of the information 4 is outside a pre-defined deviation from the reference device, the device is rejected.

Hence, this conventional system is dependant, to a large extent, on the quality of the printing on the reference device selected by the operator. In addition, it is also susceptible to outside noise, such as dust on the surface 3, and to the lighting conditions.

An inspection system in accordance with the invention for inspecting the print quality of the information 4 printed on the surface 3 is shown in Fig 3. The inspection system comprises an inspection unit 20 and a template database 14. A laser marking unit 21 is also coupled to the template database 14. The inspection unit 20 includes a camera 5 and lens 8 which is connected by the line 7 to an analog to digital converter, the output of which is coupled to a processing unit 12. A visual display unit (or VDU) 11, a keyboard 9, a trackball 10 and a bar code reader 13 are also connected to the processing unit 12.

In addition, the processing unit 12 is connected to the template database 14, which stores a number of templates for printing information 4 on surfaces of electronic devices, such as the information 4 printed on the surface 3 of the device 1. The laser marking unit 21 includes a processing unit 15 which controls a laser marker 16 which prints the information 4 on the surface 3. A bar code reader 17 is also connected to the processing unit 15.

In use, a batch of electronic devices 1 which require information 4 to be printed on the surface 3 pass along the production line to the laser marker 16. An information sheet relating to the batch, which includes a bar code containing information about the devices 1, is associated with the batch as it travels along the production line. On arrival at the laser marker 16, the bar code on the information sheet is read by the bar code reader 17. In response to the code read by the bar code reader 17, the processing unit 15 extracts from the template database 14, the template which corresponds to the information read by the bar code reader 17. The processing unit 15 then controls the laser marker 16 in accordance with the retrieved template to print the information 4 on the surface 3. After all the devices 1 have been printed, the batch may pass directly to the inspection unit 20 or to other operations on the production line between the marking unit 21 and the inspection unit 20.

At the inspection unit 20, the bar code reader 13 reads the bar code on the information sheet associated with the batch and in accordance with the bar code information, the processing unit 12 retrieves the appropriate template from the template database 14. As the bar code read by the bar code reader 13 is identical to the bar code read by the bar code reader 17, the template retrieved from the template database 14 by the processing unit 12 is identical to the template retrieved by the processing unit 15 in the marking operation. Each device 1 in the batch is then passed under the camera 5 and lens 8 and the processing unit 12 compares the image from the camera 5, digitised by the analog to digital converter 18, with the retrieved template.

The processing unit 12 carries out two operations. Firstly, it performs an optical character reading process on the information to ensure that the letters and numerals printed on the surface 3 are correct. Secondly, the processing unit 12 compares the retrieved template with the digitized image of the surface 3 to ensure that the information 4 printed on the surface 3 meet a minimum quality standard.

As the templates stored in the template database 14 represent the ideal image, a standard pre-defined rejection threshold can be set and the rejection threshold will not vary between batches. In addition, the rejection threshold will not vary between different inspection systems inspecting devices 1 from the same batch.

If necessary, an operator may enter information into the processing unit 12 via the trackball 10 or keyboard 9 and the processing unit 12 can display information relating to the inspection on the VDU 11.

As an alternative to having a separate template database 14, it is possible that there could be two copies of the appropriate templates, one copy stored on the processing unit 15 and the other copy stored on the processing unit 12. Alternatively, the templates may be stored on either the processing unit 15 or the processing unit 12 and the other processing unit may be coupled to the processing unit on which the templates are stored to retrieve the appropriate template when necessary.

Advantages of the invention are that it is not necessary for an operator to select a reference device and perform a reference reading on the inspection system 20; no decision is required by the operator and hence, the opportunity for operator error is reduced; and, the reference template is always identical and is the same as the template used for marking .

In addition, if as is normally the case, there are a number of inspection systems operating in parallel on the same batch or lot of devices, then each inspection system may retrieve the same template. This is in contrast to conventional systems in which a different reference device is presented to each inspection system. Hence, different results and different qualities of marking are accepted by each inspection system in the conventional system.

These advantages have the result of reducing the cycle time for inspection of the devices and also reduces the likelihood of acceptable markings being accidentally rejected.

Claims

1. A method of inspecting information printed on a surface comprising and capturing an image of the information printed on the surface and comparing the captured image with a reference template from which the information was printed on the surface.

2. A method according to Claim 1 wherein the information comprises alpha-numeric characters.

3. A method according to Claim 2, and further comprising optically character reading the characters and comparing the individual characters read to the corresponding characters in the template.

4. A method according to any of the preceding claims, wherein the surface on which the information is printed is a surface of an electronic device.

5. A method according to any of the preceding claims, wherein the template is retrieved by the processing unit in response to a machine readable code read by a reading device connected to the processing unit, the machine readable code being associated with the surface.

6. A method according to Claim 5, wherein the machine readable code is on an information sheet associated with the surface .

7. Apparatus for inspecting information printed on a surface comprising an image capturing device for capturing an image of the information printed on the surface; a processing unit coupled to the image capturing device and receiving an input image from the image capturing device; a memory device coupled to the processing unit, the memory device storing a template from which the information was printed on the surface; and an indicating device coupled to the processing unit; the processing unit comparing the captured image with the template and the processing unit sending a signal to the indicating device if the information printed on the surface is not within a pre-defined deviation from the template and the indicating device, in response to the signal, indicating to a user that the information printed on the surface is outside the pre-defined deviation.

8. Apparatus according to Claim 7, and further comprising a reading device coupled to the processing unit, the reading device reading a machine readable code associated with the surface and the processing unit retrieving the template in response to the code read by the reading device.

9. Apparatus according to Claim 7 or Claim 8, wherein the memory device stores a number of templates and the processing unit retrieves the template from which the information was printed in response to the code read by the reading device.

10. Apparatus according to any of the preceding claims, wherein the memory device is located remotely from the processing unit .

11. Apparatus according to Claim 10, wherein the template from which the information is printed is stored in the same memory device .