Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
  • G01N21/8901—Optical details; Scanning details
  • G01N21/8903—Optical details; Scanning details using a multiple detector array
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge

Definitions

• the present invention relates to a method for monitoring or scanning an object, material or the like with the aid of a camera which is movable in relation to the object or material.
• the invention also relates to such a system with a data-storage unit for sequential storage of recorded data as pixel values.
• the present invention is primarily intended for various types of quality control, e.g. in the production of steel tubes, rods, insulating tape for electric cables and other electrical applications, paper webs in the manufacture of paper, etc.
• pixel values are compared with a fixed reference level, usually representing a faultless state or a state without foreign substances in the object or material in question, see DE 4 200 801 A1 , for instance.
• the object of the present invention is to provide a new technology which will give increased sensitivity for detecting small changes in the object being monitored or scanned, and which will also enable selection of the sensitivity of the monitoring or scanning being undertaken.
• the object or material is scanned using a line camera and recorded data is sequentially stored as pixel values, i.e. light values, to serve as references in subsequent scans.
• pixel values i.e. light values
• the pixel value in question is not compared with a fixed basic level as is the case in conventional technology, but with a floating reference value representing the state of the object as monitored or scanned a specific time earlier.
• the sensitivity for detecting small changes in the scanned object is thus increased, and by then selecting as reference a value a longer or shorter time prior to the actual pixel, the detecting sensitivity can be regulated.
• a reference further back in time may need to 2 — be chosen than if the change is rapid. It can thus be determined that the detected change occurred during a certain period, i.e. a kind of time-derivative determination is performed.
• a change detected in the object or material may constitute some form of inhomo- geneity, foreign substances in the object or material, etc.
• the reference value is formed continuously as the mean value of a predetermined number of pixels im- mediately before the actual pixel being currently scanned.
• the momentary pixel value is thus compared with a reference value derived from earlier recent pixel values, making this embodiment suitable for detecting rapid changes in the object being monitored or scanned.
• scanned lines are stored line by line and the value of the pixel in a selected, stored line that corresponds to the actual pixel in the line being scanned, is chosen as reference value, or the mean value of the pixels in a predetermined number of selected lines of said stored lines that correspond to the actual pixel in the line being scanned, is chosen as reference value.
• These stored reference lines constitute a kind of historical record containing information on how the appearance of the scanned object has varied backwards in time. In these embodiments of the invention, thus, changes in the scanned object or material are determined over a time which can be selected by the choice of reference line.
• the change over a short interval of time is measured, which is advantageous if rapid changes shall be detected.
• the line being scanned is compared with a reference line stored further back in time, i.e. a comparison in time or a time derivative determination is performed over shorter or longer times depending on the requirements of the measurement in progress. Selecting the time over which the change shall be detected means that the detection sensitivity can also be adjusted to current needs.
• the time displacement between the stored lines in turn corresponds to a certain displacement in space of the movable object.
• a typical distance between consecu- tive lines may be 10-30 ⁇ m.
• a change in the object or material is indicated if the difference between the actual pixel value and the reference value exceeds a predetermined threshold value, or alternatively, if the difference between the actual pixel value and the reference value exceeds a predetermined threshold value in a predetermined number of consecutive pixels.
• Actual comparison of pixel values, i.e. light values, in a new, in-coming line being scanned and the selected reference line takes place pixel by pixel and when a change in one or more pixels is detected a triggsignal is suitably generated for possible further investigation of the relevant area of the object or material being scanned.
• the current "appearance" of the scanned object is compared with its previous appearance in order to detect possible changes. Both positive and negative changes can be studied and changes in the base level thus have no effect.
• the comparison unit which is arranged to form the difference between the value of the actual pixel and the reference value, comprises two subtracting units in order to determine the sign of the difference between the actual pixel value and the reference value. In this way it is possible not only to detect the occurrence of a change in the scanned object, but also to obtain information as to the nature of the change.
• the object or material in question is scanned by a line camera 2 at regular time intervals along scanning lines, and the corre- sponding light values are stored sequentially, pixel by pixel in a data-storage unit 4.
• Each line of the camera comprises pixels, i.e. light-sensitive elements, in a number of typically between 1024 and 8192.
• the pixels are read continuously with high frequency and the pixel values for up to 128 scanning lines are stored in the datastorage unit 4.
• the stored values serve as references to be used in subsequent comparisons to determine whether any pixel has changed value, i.e. to detect a change in the light value.
• up to 128 lines can be stored in the datastorage unit 4 and when a new line is stored, the oldest stored line is deleted, so that the stored lines are continuously updated.
• the above indicated number of 128 for the number of lines stored in the datastorage unit 4 is of course only an example and can be varied.
• the camera is suitably stationary while the scanned object is moved past the camera during scanning.
• the in-coming, newly scanned line is supplied to subtracting units 6, 8, to which a selected reference line is also supplied from the data-storage unit 4.
• a selector unit 10 is provided to select a specific reference line among the lines stored in the datastorage unit 4.
• the subtracting unit 6 the chosen reference line is subtracted from the scanned line that has arrived most recently, and in the subtracting unit 8 the most recent line is subtracted from the selected reference line.
• the subtraction is performed pixel by pixel.
• the use of two parallel subtracting units 6, 8 allows determination of the direction a change is taking, i.e. if the change is positive or negative.
• the subtracting unit in ques- tion delivers a corresponding output signal for comparison with a predetermined trigg level in a subsequent comparator 9, 12.
• This trigg level is adjustable.
• the subtracting unit producing a negative result delivers no output signal, i.e. either the subtracting unit 6 or the subtracting unit 8 delivers an output signal dependent on whether the change is positive or negative, and if this output signal exceeds the predetermined trigg level stored in the associated comparator 9, 12, the output step 14 of the system will deliver an output signal indicating that a change in the scanned object or material has been detected. This output signal can then be used to initiate possible further investigation, using standard methods, of the relevant area of the object or material being scanned.
• Naturally positive or negative trigg levels may be chosen for the above embodiment.
• the camera may consist of a commercially available standard camera and data- storage unit, selector, subtracting units, comparators and output step can be realized by means of an image processing circuit board.
• the pixel value in question is compared with the corresponding pixel value of a reference line stored previously in the data-storage unit 4.
• This line may be chosen from among the 128 stored lines.
• the principle of how this embodiment functions is illustrated in Figure 2.
• the pixel value in question in the relevant line is 125, indicated in suitable units, and the stored line 10 has been chosen as reference line.
• the corresponding pixel value of this reference line is 119 and the difference between the reference value and the pixel value in question is thus -6 which, in this example, is sufficient to generate an output signal from the associated comparator.
• Figure 3 shows an alternative embodiment in which the reference value is determined by forming an average value in the actual scanning line from a predetermined number of pixels immediately prior to the actual pixel.
• the reference value is obtained from the mean value of the four pixel values immediately prior to the actual pixel.
• the mean value in the example shown is 106 and the actual pixel value of the actual line is 25.
• the trigger level set in the associated comparator is -45. In this case, thus, the output step 14 will deliver an output signal too.
• the actual pixel is compared with the immediately pre- ceding pixels in the same scanning line, which makes the system particularly sensitive to rapid changes.
• Figure 4 illustrates yet another alternative embodiment in which the actual pixel value is compared with a reference value consisting of the mean value of corre- sponding pixels in a predetermined number of lines chosen from amongst the previous lines stored.
• the mean value is formed from the preceding lines 1-10, i.e. the reference values consists of the mean value of ten previous pixel values at the same position in the lines.
• the mean value of the pixels in question is 65.
• the trigg value in the associated comparator for deliv- ering an output signal is -45 in the example.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• General Health & Medical Sciences (AREA)
• Textile Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Closed-Circuit Television Systems (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Image Processing (AREA)
• Image Analysis (AREA)
• Geophysics And Detection Of Objects (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=20410844

Family Applications (1)

Country Status (6)

Families Citing this family (2)

Family Cites Families (6)

• 1998
  • 1998-04-02 SE SE9801170A patent/SE9801170L/ not_active Application Discontinuation
• 1999
  • 1999-03-31 WO PCT/SE1999/000541 patent/WO1999051969A1/en not_active Application Discontinuation
  • 1999-03-31 EP EP99922695A patent/EP1086368A1/de not_active Withdrawn
  • 1999-03-31 JP JP2000542657A patent/JP2002510815A/ja active Pending
  • 1999-03-31 CA CA002324112A patent/CA2324112A1/en not_active Abandoned
• 2000
  • 2000-09-26 NO NO20004821A patent/NO20004821L/no not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events