DE2318849A1 - METHODS FOR OPTICAL READING OR OPTICAL INSPECTION OF OBJECTS, SUCH AS CONTAINERS OR DGL - Google Patents

Description

SUBJECT: Procedures for optical readout or optical testing of objects such as containers or the like.

As an optical check, the check of an object is to be used here visually recognizable properties, e.g. size, correct positioning, cleanliness the surface, color, presence of damage, etc. can be understood. A A typical example is the testing of transparent glass containers, e.g. bottles, for foreign bodies, washing residues, damage, etc. Optical selection is finding out of objects of a certain shape from a variety of different objects, for example the evaluation of chromosome images by counting certain chromosomes Form from a multitude of different possible forms.

So far, such tests are usually carried out with the human Eye carried out, which either directly or by means of observation devices the subject itself or a picture of the object, e.g. also on a television screen, observed. The working speed of the human Eye and its ability to recognize differences in the visually perceptible properties can be reliably determined, but are limited. The invention aims to be a to create a test method working with optical scanning of the object the speed of work, accuracy and reliability versus skills the human eye can be significantly increased and in which the test result an actuation signal automatically without human intervention, e.g. for an alarm device, a registration device or a control device for automatic exclusion of the object from a work process.

According to the invention, this is achieved by an image of the object on the screen of an electronic image scanning device (Vidicon tube) generated and the output signal of the image scanning device an electrical signal evaluation device feeds.

The previously known method will be used even if, for example, because of poor accessibility of the test object not observed this itself, but a; TV picture of the object is generated, this TV picture is only observed optically. In the case of the method according to the invention, on the other hand, the Image scanning of the object as an aid for electronic signal evaluation, which is automatic supplies a test result which is registered or used e.g. for tax purposes can be. For example, when scanning clear bottles, sudden The peaks of the brightness signal indicate the presence of debris, dirt or sores indicate in the glass and z.D. the exclusion of the bottle from a subsequent filling process steer.

It is advantageous to use the output when evaluating the signal Compare the signal with a given comparison signal. This comparison signal can be generated in any way and provides a setpoint for a specific, property of the object to be tested. Provides the signal evaluation device a Difference between the comparison signal and the output signal of the image scanning device fixed, it can do this as a measurement result e.g. for a size, shape or position deviation of the test object from the target value.

In an advantageous manner, one can use the comparison signal in this way produce that one of the signal evaluation device, the output signal one with the Image scanning device chronized the second image scanning device for comparison signal and a signal corresponding to the difference between the two output signals generated. The second Image scanning device can be a comparison object scan.

The visual comparison of a test object with a comparison object is in itself commonplace in measurement and testing technology; what is essential here is that that Comparing the image scanning signals by way of electronic signal evaluation takes place, for example generating an output signal from the Si ¢; can, if amplitude, lwidth, frequency, number, steepness or the like. of the output pulses the image scanning device exceed or fall below a target value.

"Figure" in the sense used here does not have to be a real one Image that reproduces the object recognizably can be understood. Figure in Within the meaning of the invention, any generated on the screen of the image scanning device can be used Light distribution that provides complete information about each to be tested contains optical property of the object. In particular, the imaging beam path be influenced by filters, diaphragms or other optical means so that the "Image" does not reproduce the object itself in a recognizable manner, but essentially only the presence and location of defects, impurities or the like.

indicates.

According to the invention, this can be achieved in particular by the fact that one illuminates the object with coherent light (laser light) and that of the object to the image scanning device: tea-scattered or reflected coherent Lets light pass through a holographic filter.

A hologram in particular can be used as the holographic filter i.e., a photographic plate on which superposition and interference of two coherent rays, one of which is scattered or reflected on the object was, a blackening pattern was generated, which iii encrypted form a Contains complete information about the appearance of the object. Usually serves such a hologram in addition, uril one that reproduces the object in three dimensions Generate image, and it is irradiated with laser light for this purpose. According to the invention, however, such a hologram is used differently. That The hologram is made using a first object, in particular one that is free of defects Sample object, produced and then used as a filter in the way of a second object, in particular the respective test object, coming coherent light. It then acts as a filter by removing those parts of the coherent one Light that contain the information about common features of the two objects, and on the other hand the proportions, the deviations of the test object from the standard object corresponding, directs in different spatial directions or at different locations the image scanning device concentrated, so that one or the like by suitable diaphragms. can achieve that the scanning device hur light information of the one or other type scans.

Another possibility is to use a so-called "Character recognition hologram", which is in the focal plane of one of the test object incoming light is arranged parallel lens (Fourier plane). Known is the use of character recognition holograms in automated recognition of characters or the like. The hologram is made using a specific Character produced as a template. From a test object, e.g. a written page, which contains one or more such characters can then by means of coherent Light creates an "image" using the character recognition hologram in the places where oaks of the respective species are available bright points of light appear. In adaptation to the present invention applied this method in such a way that, firstly, the hologram is not from a character, but from a typical recognizable structure, e.g. the sharp-edged spillage a glass bottle, and second, the one filtered through the hologram "Figure" on which the locations of the corresponding defects appear as bright points, by the Bildabtasvorrich Lunr: is scanned. This results in very large, deflections of the scanning signal that are well suited for electronic evaluation.

From a mathematical point of view, one effects the use of a hologram a spatial correlation of the light distribution coming from the object with a through given the hologram Light distribution that is a standard comparison object is equivalent to. This correlation can be used to determine the ratio of the useful signal to the background can be significantly improved.

According to another embodiment of the method according to the invention but it is also possible to correlate the output signal over time with electronic means perform the image scanning device with a predetermined waveform and thereby also the influence of the subsurface, e.g. that of the fault-free areas of the Object of scattered light, switch off. For example, each scan line can be marked with a or correlate several temporally preceding lines (autocorrelation) or one can see the correlation between the sample signal and one through the sample of a comparison object (cross-correlation). This can be done in each case by an electronic device connected to the image scanning device Correlator take place.

The invention also relates to a device for performing the Method with an electronic image scanning device operating line by line (Vidicon tube) and optics for imaging a test object on the screen of the Image scanning device. Such a device is characterized in that on the image sensing device is connected to a measurement signal processing logic circuit is the pulse frequency when exceeding or falling below a specified pulse shape or the like. triggers a warning and / or control signal. In particular, the facility Means for generating one to be fed to the signal processing logic circuit Comparison signal on.

The device generating the comparison signal is preferred a second line-by-line electronic image scanning device which is associated with the first image sensing device is synchronized.

Type and shape of the test object and the type of its lighting and Figure can in principle be any, but it is advantageous if those Output signals of the image scanning device, the test characteristics deviating from the normal value of the object, have the greatest possible contrast to the background. Therefore, the device preferably has a lighting device for the Test object, which is designed so that only light scattered on the object to the image scanning device got. This means, for example, when checking transparent bottles, that no light to the image scanning device from the clean and faultless glass wall but only from contamination, foreign bodies or damage to the Glass wall. This results in large, high-contrast amplitudes of the brightness signal the image scanning device, which is particularly good for the subsequent electronic Suitable for signal evaluation.

The signal quality can also be improved by using pulsed light the illumination of the object can be improved, the image scanning device is preferably operated synchronously with the pulsed light.

An embodiment of the invention will be described in the following with reference to the drawings explained in more detail.

Fig. 1 shows a schematic diagram of a measuring arrangement for the implementation of the procedure.

Fig. 2 shows a schematic diagram of the measuring arrangement seen from above with a block diagram of the pulse evaluation unit.

3 shows another arrangement for carrying out the method.

According to FIG. 1, a bottle placed on a support surface 1 is shown 2 illuminated by means of a light beam, which is indicated by a lamp Light source 3 emanates through an optics indicated as lens 4 in a focal point 5 is concentrated, and from this point diverges into the bottle opening entry. The focal point 5 is a point of intersection for all rays of the light bundle and an intermediate image of the light source 3. It lies at the level of the neck 7 of the bottle 2 or a little above, so that the outer boundary rays 6, 6t of the light bundle run approximately tangential to the beveled shoulders 8 of the bottle. To this Way is achieved that especially the inner surface of the shoulders 8, where experience has shown Foam deposits form, are well lit and not in the shadow of the light lie. If there are no foreign bodies on the illuminated inner surfaces of the bottle 2 or impurities, no light is emitted from that limited by the rays 6, 6 ' Beams of light scattered out. If, on the other hand, there is a foreign body on the inner surface, so this can scatter the light so that it passes through the transparent Wall the bottle 2 enters the outside and can be detected there. This gives you one that reproduces the contaminants to be detected with particularly high contrast Lighting arrangement that is particularly advantageous for the method according to the invention is. However, the method is in principle also possible with other lighting arrangements and can be carried out on other test objects.

ie the device scanning the object and generating the output signals is shown in the left part of FIG. It consists of one through a lens 13 indicated optics and an image scanning tube (Vidicon tube) 14, in which a Anode 15 on which the object is imaged and its local conductivity of the exposure intensity is dependent, by an electron beam 16 lines.

is scanned wisely. Optics 13 and Vidicon tube 14 form together an arrangement similar in principle to a television camera. Stray light emitted by Contamination 17 originating on the inner surface of the bottle 2 is caused by the optics 13 focused on a certain point of the photo anode 15, and when scanning this Place through the sheet metal electron beam 16 results at the exit of the Vidicon tube Signal pulse.

The object can also be scanned from several sides, as with the The arrangement shown from above in FIG. 2 Here is at 18 a Conveyor belt or some other conveying device denotes the bottles 2 one after the other the measuring point 19 supplies, in which the bottles by means of the light source in the out Fig. 1 visible way are illuminated.

The scattered light emitted by impurities or foreign bodies is collected by four line-scanning receivers 20, 20 'distributed around the measuring point 19, each consisting of an optic and a vidicon tube.

These receivers 20, 20 'or the receiver 14 in FIG. 1 are connected to a Signal pulse evaluating logic circuit connected, which is in the character bullet; the For the sake of simplicity, it is only shown schematically in FIG. 2 for the receiver 20 '. At an input 21, pulses for synchronizing the line scan with fed to the cycle of the conveyor 18.

An output 22 of the line scanning receiver 20 'is connected to a monitor 23 with picture display tube connected for control and adjustment, in order to synchronize its line run with that of the receiver 20 '. At the exit 23 of the receiver 20 ', the actual signal pulses are picked up during scanning contamination or a foreign object occur. These are also called ~ Hell / dark signals are fed to the monitor 23. In addition, the output 23 is with a pulse evaluating Logic circuit connected, indicated as a whole by the dashed box 24 is. In its simplest form it contains logic an amplifier 25 and a pulse height discriminator 26, so that only pulses that have a predetermined, preferably exceed the adjustable threshold amplitude, at the output 27 as control signals appear. Instead, or in addition, in the logic circuit 24 further impulse or

signal processing elements, such as pulse width discriminators, Differentiators, integrators, frequency filters and frequency converters.

In the illustrated embodiment, the logic circuit is detecting 24 only those dirt particles or foreign bodies that are scattered light from a certain Cause minimum intensity. When using a pulse width discriminator the extent of the scattering object can also be detected. Another Embodiment can additionally contain an integrator. This adds up the total number of pulses emitted by the Vidicon tube, i.e. one Integration over the amount and size of the scattering objects. A subsequent threshold link or a discriminator generates an output signal when the integrated signal exceeds a certain value. This can be achieved that bottles with a cloudiness can be singled out. A haze may not have any Scattering centers, the size or brightness of which is in itself enough to address the device would be enough.

By further expanding the logic circuit 24 it can be achieved that other criteria, e.g. the edge steepness of the signal pulses (first Differentiation) or the curvature of the impulse course (second differentiation) be used to discriminate. This can be used for special features Eliminate the scattered light, e.g. from the bottle limitation or from outside Features of the bottle, e.g. embossed letters, scratches or the like. originates. In particular, specific soiling, such as cigarette butts, Make out ash, egg white or lye residue.

Another expansion of the logic circuit is when using a color vidicon tube possible through the discrimination according to color values. For example, you can use the bottle respectively.

the container to be tested against a background with a certain Let the basic color run. This allows the device to last as long remains switched off as the Vidicon tube scans the background. Furthermore can by a delay element that occurs when the edge of the bottle enters the field of vision generated pulse jump can be suppressed.

The output signal appearing at the output 27 of the logic circuit 24 can be used to trigger an alarm signal and / or to automatically remove the faulty bottle be used. - For example, it can Output signal the pivoting of a switch 28 into the path of the bottles on the Effect conveyor 18, so that the bottles to be sorted out on a branch track 29 or the like. to get distracted. Such controllable switches for deflecting faulty ones Containers from the delivery flow are in themselves, also in other designs, e.g. as rotating drums or the like., Known.

As a light source 3 for illuminating the container, in particular a laser can be used. The wavelength of the light used for the measurement can be in the visible or m1visible range, but must be out of the obvious Reasons lie in the permeability range of the material of the container 2. The laser or the light source is preferably operated in pulses, the pulse force preferably with the pulse rate or the frame rate of the scanning device 20, 20 'is coupled. Both can be cyclically controlled by the passage of the container be. You can choose the pulse duration so short that practically a "snapshot" of the moving object to be measured is generated or. the signal evaluation is based on.

One can - what is not shown - to the signal processing Logic circuit 24 also connect another image scanner, which a comparison object is scanned, e.g. a clean one, but otherwise in the same way illuminated Bottle. By superimposing the ones supplied by the two image scanners Signals in the logic circuit can be achieved that only deviations of the test object are detected by the comparison object, but not such fluctuations in the brightness signal, those of common features of the two objects, e.g. their edges, impressions or the like., originate. Differences in position of the test object and comparison object in the respective field of view one can in the logic circuit with the help of delay elements take into account which result in non-simultaneous occurrences in the individual lines Signal deflections, e.g. from the contours of the differently positioned objects originate, but are still correctly superimposed.

In the embodiment according to FIG. 3, a laser 30 comes with it Upstream optics parallel, coherent light via e.g. a beam splitter plate 30a to a test object, e.g. the mouth 31 of a bottle 32, which is on a conveyor belt 33 is moved past the measuring point. That sprinkled upwards from the mouth of the bottle or reflected light arrives, possibly via a lens indicated Optics 34, on a filter plate 35, which has a hologram as a blackening pattern. In particular, it is a hologram which is from an error-free standard object was produced. Another optic 36, indicated as a lens, focuses this through the filter plate 35 is transmitted light on the screen 37 of an image sensing device 38 (Video camera). The interaction of the light scattered by the bottle mouth with the hologram is such that all the light is united in a focal point 39 is, the device 38 scans only a single point of light, if the Bottle mouth 31 exactly corresponds to that of which the hologram was created, i.e. is error-free. However, the bottle mouth 31 to be tested contains deviations from the standard object, e.g. a sharp-edged chipping 40, then this is the cause for the fact that light also reaches other places than the focal point 39 and e.g. each a discrete figure of light depending on the type of radiation path and hologram used 41 generated outside the point 39 or a diffuse halo. One can cover point 39 with a mask or by electronic control of the scanning device 38 filter out and then receives a scanning signal of the scanning device 38, which only responds to light outside the point 39, i.e. to light which is caused by errors of the test object. If the bottle 32 moves with the during the measurement Belt 33 in the direction of arrow 42, point 39 also moves on a path, e.g. 43, over the scanning screen, so that when evaluating the light outside of this Must capture web.

Numerous modifications of this arrangement using the usual ones holographic techniques are possible. So you can use the hologram 35 instead of create an error-free sample object also from a typical error structure, whereby one then also on the screen 37 a characteristic and good of the scan accessible light distribution. Overall, the holographic ones mentioned are suitable Methods for generating a light distribution particularly suitable for scanning mainly for essentially flat test objects such as the ring-shaped bottle mouth.

If objects with greater spatial depth are to be detected, then additional equipment such as image converters required.

Claims (11)

P a t e n t a n s p r ü c h e Method for the optical testing of workpieces, containers or the like. Objects, thereby g e k e k e n n z e i c h -n e t, that one is an image of the object generated on the screen of an electronic image scanner (Vidicon tube) and the output signal of the image scanning device of an electrical signal evaluation device feeds, e :. Expiry according to claim 1, characterized in that When evaluating the signal, the output signal is compared with a specified comparison signal compares. 3. The method according to claim 2, characterized in that g e k e n n -z e i c h n e t, that one d.er Signalauswerteinrichtung the Husgangssignal one with the image scanning device synchronized second image sensing device supplies as a comparison signal and a signal corresponding to the difference between the two output signals is generated. 4. The method according to any one of claims 1 to 3, characterized g e k e n n z e i c h n e t that an output signal of the iiß: nalauswerteinrichtung then one generated when amplitude, width, frequency, number, slope or the like. of the output pulses the Image scanning device exceeds or exceeds a target value fall below. 5. Device for performing the method according to one of the claims 1 to 4, with an electronic, cell-by-cell image scanning device (Vidicon Stirrer) and optics for mapping a test object onto the screen of the Image scanning device, characterized in that it is attached to the image scanning device a measuring signal preprocessing logic circuit is connected, which in the event of a deviation of the measurement signal of a predetermined pulse shape, pulse frequency or the like. a warm and / or triggering the control signal. 6. Apparatus according to claim 5, g e k e n n z e i c h -n e t through Means for generating one to be fed to the signal processing logic circuit Comparison signal. 7. Apparatus according to claim 6, characterized in that g e k e n n -z e i c h n e t that the device generating the comparison signal consists of a second, line-by-line working electronic image scanning device (Vidicon tube) with the first is synchronized. 8. Device according to one of claims 5 to 7, characterized g e k e n n n e i n e t that they are a Selencktungseinrichtung for that Has test object, which is designed so that only light scattered on the object arrives at the image scanner. 9. The method according to any one of claims 1 to 4, characterized g e k e n n Do not admit that the object is illuminated with coherent light (laser light) and the coherent scattered or reflected from the object to the image sensing device Lets light pass through a holographic filter. 10. The method according to claim 9, characterized in that g e k e n n -z e i c h n e t that the coherent light emanating from object points can be obtained with the aid of a lens transformed into parallel light blinds and arranged in the focal plane of the lens by a holographic character recognition filter lets pass, and the light with another Lens refocused at the appropriate distance and direction. 11. The method according to any one of claims 1 to 4, characterized g e k e n It is not clear that electronic means can be used to establish a temporal correlation the output of the image sensing device with itself or with a comparison signal carries out.