WO2011013153A1 - Automated apparatus of optical inspection of containers and related automated method of inspection - Google Patents

Automated apparatus of optical inspection of containers and related automated method of inspection Download PDF

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Publication number
WO2011013153A1
WO2011013153A1 PCT/IT2010/000317 IT2010000317W WO2011013153A1 WO 2011013153 A1 WO2011013153 A1 WO 2011013153A1 IT 2010000317 W IT2010000317 W IT 2010000317W WO 2011013153 A1 WO2011013153 A1 WO 2011013153A1
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WIPO (PCT)
Prior art keywords
container
axis
determining
dimensional
cameras
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PCT/IT2010/000317
Other languages
French (fr)
Inventor
Sanzio Caroli
Marco Casadio
Original Assignee
Sacmi Cooperativa Meccanici Imola Societa Cooperativa
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Publication of WO2011013153A1 publication Critical patent/WO2011013153A1/en

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T7/00—Image analysis
    • G06T7/0002—Inspection of images, e.g. flaw detection
    • G06T7/0004—Industrial image inspection
    • G06T7/001—Industrial image inspection using an image reference approach

Definitions

  • the present invention concerns an automated method of optical inspection of containers, in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, that allows in a precise, simple, versatile, reliable and efficient way, to recognise possible defects of such containers, in particular for determining the correct application and integrity of the related labels, during movement of containers along a conveyor belt according to any a priori unknown angular orientation.
  • the present invention further concerns the automated apparatus of inspection executing the method.
  • containers such as bottles, bowls, and vessels, wherein powdered substances, gels and liquids, preferably food and beverages, are stored, are intact and devoid of defectivities of any type.
  • such containers are provided with labels applied on the external walls showing indications established by law rules and identifiers, preferably barcodes, allowing them to be tracked from the packaging factory to the end user.
  • European Patent Application No. 872724 A2 discloses a method and an apparatus for the external check of containers, in particular for checking labels applied on bottles, wherein a camera acquires images of containers placed on respective supporting discs which arrives in a detection zone through a conveyor belt. In the detection zone, a mechanism rotates each container about its own axis by a predefined angle within the interval ranging from 380 to 420 degrees, so that the camera sends a plurality of acquired images during rotation of the container to an electronic unit that reconstructs and analyses the images of the whole side surface of each container.
  • prior art devices and equipments of automated optical inspection of containers suffer from some drawbacks.
  • an automated method of optical inspection of containers in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, wherein one or more cameras acquire two or more images of a container moved by a conveyor belt when the container is in at least one optimal inspection position within an inspection chamber, the method being characterised in that it performs a procedure of rectification onto a plane of at least one portion of a side surface of the container on the basis of said two or more acquired images comprising the following steps:
  • A.1 determining at least one univocally defined reference three- dimensional axis of the container starting from said two or more acquired images
  • step A.2 positioning a three-dimensional model of the container stored in a memory unit on said at least one reference three-dimensional axis as determined in step A.1;
  • A.3 forming a planar image of said at least one portion of the side surface of the container, wherein each two-dimensional point (u, v) corresponds to a specific three-dimensional point (x, y, z) of the selected three-dimensional model in said two or more acquired images according to a mathematical correspondence indicative of a spatial positioning of said one or more cameras with respect to the container when the latter is positioned in said at least one optimal inspection position.
  • the rectification procedure may further comprise the following final step:
  • A.4 determining possible defects of said at least one portion of the side surface of the container, preferably of one or more labels applied thereon.
  • said three-dimensional model of the container may comprise at least one array of points belonging to at least one portion of an external surface of the container, preferably angularly equispaced and/or equispaced in height.
  • the container may be a body of revolution
  • said at least one reference three-dimensional axis may be an axis of rotation of the container
  • step A.1 may comprise the following substeps:
  • determination of the axis of the container in each one of said two or more acquired images is preferably carried out in one of the ways selected from the groups comprising:
  • the container may be a body not of revolution, and at least one of said two or more acquired images may be a, preferably top, plan image of the container.
  • the method may execute, preferably periodically, a calibration procedure comprising the following steps:
  • the method may execute a procedure of storing at least one two-dimensional shape of the container comprising the following steps:
  • the storing procedure further preferably comprising the following step: C.3 constructing and storing said three-dimensional model of the container,
  • the storing procedure further more preferably comprising the following step:
  • the container may be a body of revolution
  • said at least one reference three-dimensional axis may be an axis of rotation of the container
  • step C.1 may comprise the following substeps:
  • determination of the axis of the container in each one of said two or more acquired images is preferably carried out in one of the ways selected from the groups comprising:
  • step C.1 preferably determines a generating curve of said body that is preferably stored in step C.2.
  • the container may be a body not of revolution, and at least one of said two or more acquired images may be a, preferably top, plan image of the container.
  • the method may further comprise the following preliminary steps:
  • an automated apparatus of optical inspection of containers in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, comprising an inspection chamber crossed by a conveyor belt and provided with one or more cameras controlled by a controlling and processing unit provided with a memory unit, said one or more cameras being capable to acquire two or more images of a container moved by the conveyor belt when the container is in an optimal inspection position within the inspection chamber, said two or more images being sent to the controlling and processing unit, the apparatus being characterised in that the controlling and processing unit is capable to execute the automated method of optical inspection of containers as previously described.
  • said cameras may be at least four, four cameras being preferably placed at the four vertices of a rectangle, more preferably pairwise opposed, still more preferably mounted on respective mechanical devices for adjusting height and, even more preferably, for adjusting orientation.
  • said one or more cameras may comprise at least one camera oriented according to an axis orthogonal to the plane of the conveyor belt, so as to acquire a, preferably top, plan image of the container.
  • the apparatus may be further provided with detecting electronic means, connected to the controlling and processing unit, capable to detect when a container moved by the conveyor belt is in said optimal inspection position, said detecting electronic means preferably comprising a sensor, more preferably an optoelectronic sensor, connected to the controlling and processing unit and an encoder connected to the conveyor belt.
  • Figure 1 schematically shows a perspective view of a preferred embodiment of the apparatus according to the invention
  • Figure 2 shows a top view of a portion of the apparatus of Figure 1
  • Figure 3 shows a perspective view of a sectioned portion of the apparatus of Figure 1;
  • Figure 4 shows a perspective view of a particular of the apparatus of Figure 1 ;
  • Figure 5 shows an example of acquired images from the cameras of the apparatus of Figure 1 during the calibration procedure
  • Figure 6 shows an example of acquired images from the cameras of the apparatus of Figure 1 during the procedure of storing the shape of a container.
  • a preferred embodiment of the apparatus 1 comprises an inspection chamber of octagonal plan, accessible through a front hatch 2 and a rear hatch 3, which inspection chamber is crossed by a conveyor belt 4 for moving containers, such as bottles, bowls and vessels, to be inspected.
  • the conveyor belt 4 is flanked by side bars 15 at the inlet and outlet of the inspection chamber for guiding the containers.
  • a sensor 5 preferably an optoelectronic one, is located so as to detect when a container, represented in Figures 2 and 3 as a large bottle 6 or as a small bottle 6', that is moved by the conveyor belt 4, begins to occupy a central zone of the inspection chamber.
  • Two interspaces are provided at the sides of the conveyor belt 4 which are of size sufficient to let containers 6" falling from the same belt pass.
  • the detection signal of the sensor 5 is used for determining when the container (6 or 6') is in an optimal position, preferably corresponding with the centre of the inspection chamber, wherein four cameras 7 simultaneously acquire respective images of the same container.
  • the four cameras 7 are preferably arranged at the four vertices of a rectangle, more preferably pairwise opposed, and they are housed in proper angular seats 8 accessible from outside by removing respective angular protective chassis 9.
  • each camera 7 is preferably mounted on a mechanical device 10 for adjusting height and, more preferably, adjusting orientation of the same camera 7.
  • An inner wall 11 allows the objective only of the respective camera 7, sliding within a vertical slot 12 (depending on the height determined by the mechanical device 10), to be visible from inside the inspection chamber, as shown in Figures 3 and 4, in particular hiding the mechanical device 10.
  • the sensor 5 and the four cameras 7 are connected to a controlling and processing unit 13, provided with a monitor 14, preferably an adjustable one, for displaying the outcome of inspections.
  • the unit 13 is capable to determine, on the basis of the signal coming from an encoder (not shown) connected to the conveyor belt 4 and also on the basis of the known size of the moved container (6 or 6'), the instant at which the container is in the optimal position, preferably corresponding with the centre of the inspection chamber, wherein the four cameras 7 simultaneously acquire respective images of the same container.
  • the unit 13 controls the cameras 7 making them acquire simultaneous images of the container, which images are sent to the unit 13 for processing them in order to identify its possible defects.
  • the controlling and processing unit 13 executes an automated method of inspection, through a memorised software, as described in the following.
  • One of the usable calibration techniques may be, by way of example, the technique described by Roger Y. Tsai in "A Versatile Camera Calibration Technique for High-Accuracy 3D Machine Vision Metrology Using Off-the-Shelf TV Cameras and Lenses", IEEE Journal of Robotics and Automation, Vol. RA-3, No. 4, August 1987.
  • the calibration step provides to frame a same non-planar object of calibration simultaneously with all the cameras 7. Hence, each camera acquires a respective portion of the calibration object, obtaining four images as shown, for instance, in Figure 5.
  • the unit 13 identifies the coordinates of the notable points in terms of planar coordinates of the images (u, v), so as to determine for each camera the correspondences between the notable points (u, v) identified on the images and three-dimensional points (x, y, z). As a consequence, the unit 13 is capable to obtain a mathematical correspondence (given by a matrix of intrinsic and extrinsic parameters characteristic of each camera) between the three-dimensional points and the homologous two- dimensional points.
  • the spatial position of the cameras 7 is known with respect to the calibration object and, consequently, within the inspection chamber.
  • the calibration procedure of the apparatus may be repeated whenever there occur setting and/or structural modifications.
  • the four cameras 7 acquire respective simultaneous images of the same container.
  • the controlling and processing unit 13 is capable to execute a procedure for storing the shape of the same container, constructing a three-dimensional model of the container, provided that it is assimilable to a body of revolution.
  • the so constructed three-dimensional model may be stored in the unit 13 or used for comparing it with a reference three-dimensional model previously stored in the unit 13 in order to determine possible defects of the same container (e.g., in case of bottles to inspect, for checking that the diameter of the bottles has an established size).
  • Such storing procedure comprises a step of identifying the three- dimensional rotation axis of the container starting from the identification of the axes in the two-dimensional acquired images. This allows to correct possible perspective errors present in the two-dimensional images acquired by the cameras. Afterwards, the unit 13 executes a step of identifying the contour of the container, or the generating curve of the three-dimensional model, as best approximation of the set of contours obtained in the two-dimensional images with respect to the previously identified three-dimensional axis.
  • identification of the three-dimensional axis of the container may comprise the following steps:
  • the three-dimensional axis may be determined as the straight line minimising the distance from the so determined planes).
  • Determination of the container axis in each two-dimensional image may be carried out in several ways. By way of example, it is possible to determine on each two-dimensional image the left and right symmetrical edges of the container, and to determine the median line as two- dimensional axis. Alternatively, the container axis in each two-dimensional image could be determined as the orthogonal line passing through the median point of the cap and/or of the neck and/or of the bottom of the container.
  • the controlling and processing unit 13 is capable to execute a procedure of rectification onto the plane of the side surface of the container.
  • Such rectification procedure comprises a step of identifying the three-dimensional rotation axis of the container starting from identification of the axes in the acquired two-dimensional images, similarly to what previously seen for the procedure of storing the shape of the container.
  • the rectification procedure comprises a step of positioning the (known) three-dimensional model of the container on the three-dimensional axis so indentified for the container under examination.
  • such three-dimensional model is an array of points angularly equispaced and equispaced in height on the external surface of the container that is desired to rectify.
  • the rectification procedure comprises a step of forming a planar image of the external surface of the container, wherein for each three-dimensional point (x, y, z) of the three-dimensional model (previously positioned on the three-dimensional axis of the container under examination) it is formed the output rectified image by taking the corresponding two-dimensional point (u, v) (thanks to the mathematical correspondence identified in the calibration step) of the image of the camera closer to the same three-dimensional point (x, y, z).
  • the image that is formed represents the external surface of the unrolled container.
  • Such rectified image of the external surface may be used by the unit 13 for determining possible defects, for instance, of one or more labels, e.g. thermal shrinking ones, applied on the external surface of the container under examination.
  • labels e.g. thermal shrinking ones
  • the apparatus is advantageously provided with a further top camera (or bottom camera, if the conveyor belt is transparent) that acquires a top plan image (or a bottom plan image, if the conveyor belt is transparent) on the basis of which the controlling and processing unit 13 is capable to determine the container orientation on the basis of the known three-dimensional model (as polygonal mesh) of the same container.
  • the unit 13 would determine the container orientation preferably on the basis of the recognition of a univocally defined reference axis of the three-dimensional model. Possibly, such three-dimensional model could be also directly obtained by the unit 13 on the basis of the images acquired by the cameras. Also such further camera undergoes a calibration procedure similarly to what seen above.
  • the controlling and processing unit 13 is capable, on the basis of a sequence of subsequent images acquires by the cameras, to determine which acquired images are the ones wherein the container is in the optimal (preferably central) position of inspection.
  • the procedure for storing the shape of the containers is not an essential feature of the apparatus.
  • the controlling and processing unit 13 may simply only execute the calibration procedure and the procedure of rectification onto the plane of the side surface of the containers.
  • the calibration procedure could be made only once at the end of the apparatus assembly in the factory, whereby the controlling and processing unit 13 could then only execute the procedure of rectification onto the plane of the side surface of the containers.
  • inventions may comprise a number of cameras different from four.
  • the essential feature is that the acquired images are sufficient to take the whole side surface (and, in case of bodies not of revolution, a plan view) of the container.
  • the apparatus may be provided with a shooting system with cameras comprising at least one camera and provided with one or more mirrors and/or mechanical devices for moving said at least one camera and/or said one or more mirrors.

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  • Engineering & Computer Science (AREA)
  • Quality & Reliability (AREA)
  • Computer Vision & Pattern Recognition (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)

Abstract

The present invention concerns an automated method of optical inspection of containers (6, 6'), in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, wherein one or more cameras (7) acquire two or more images of a container (6, 6') moved by a conveyor belt (4) when the container (6, 6') is in at least one optimal inspection position within an inspection chamber, the method being characterised in that it performs a procedure of rectification onto a plane of at least one portion of a side surface of the container (6, 61) on the basis of said two or more acquired images comprising the following steps: A.1 determining at least one univocally defined reference three- dimensional axis of the container (6, 6') starting from said two or more acquired images; A.2 positioning a three-dimensional model of the container (6, 6') stored in a memory unit on said at least one reference three-dimensional axis as determined in step A.1; A.3 forming a planar image of said at least one portion of the side surface of the container (6, 6'), wherein each two-dimensional point (u, v) corresponds to a specific three-dimensional point (x, y, z) of the selected three-dimensional model in said two or more acquired images according to a mathematical correspondence indicative of a spatial positioning of said one or more cameras (7) with respect to the container (6, 6') when the latter is positioned in said at least one optimal inspection position. The present invention concerns the apparatus that executes such a method.

Description

AUTOMATED APPARATUS OF OPTICAL INSPECTION OF CONTAINERS AND RELATED AUTOMATED METHOD OF INSPECTION
The present invention concerns an automated method of optical inspection of containers, in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, that allows in a precise, simple, versatile, reliable and efficient way, to recognise possible defects of such containers, in particular for determining the correct application and integrity of the related labels, during movement of containers along a conveyor belt according to any a priori unknown angular orientation.
The present invention further concerns the automated apparatus of inspection executing the method.
It is known that processes for packaging food and beverages provide that containers, such as bottles, bowls, and vessels, wherein powdered substances, gels and liquids, preferably food and beverages, are stored, are intact and devoid of defectivities of any type.
In particular, such containers are provided with labels applied on the external walls showing indications established by law rules and identifiers, preferably barcodes, allowing them to be tracked from the packaging factory to the end user.
During packaging processes, it is hence necessary to ascertain the integrity and defectivity absence of the containers and, in particular, the correct application and integrity of the labels on the external walls of the containers.
In the last decades a series of devices and equipments have been developed which allow an a utomated optical inspection or AOI of the containers during packaging processes.
European Patent Application No. 872724 A2 discloses a method and an apparatus for the external check of containers, in particular for checking labels applied on bottles, wherein a camera acquires images of containers placed on respective supporting discs which arrives in a detection zone through a conveyor belt. In the detection zone, a mechanism rotates each container about its own axis by a predefined angle within the interval ranging from 380 to 420 degrees, so that the camera sends a plurality of acquired images during rotation of the container to an electronic unit that reconstructs and analyses the images of the whole side surface of each container. However, prior art devices and equipments of automated optical inspection of containers suffer from some drawbacks.
First of all, the algorithms for reconstructing and analysing the images of the whole side surfaces of the containers are rather complex and, sometimes, unreliable, occasionally requiring a specific orientation of the containers on the conveyor belt.
Moreover, devices and equipments requiring a rotation of the containers have particularly complex operation and maintenance.
It is therefore an object of the present invention to allow, in a precise, simple, versatile, reliable and efficient way, an optical inspection of containers, in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances, gels and liquids, preferably food and beverages, so as to recognise possible defects of such containers, in particular for determining the correct application and integrity of the related labels, during movement of containers along a conveyor belt according to any a priori unknown angular orientation.
It is specific subject matter of this invention an automated method of optical inspection of containers, in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, wherein one or more cameras acquire two or more images of a container moved by a conveyor belt when the container is in at least one optimal inspection position within an inspection chamber, the method being characterised in that it performs a procedure of rectification onto a plane of at least one portion of a side surface of the container on the basis of said two or more acquired images comprising the following steps:
A.1 determining at least one univocally defined reference three- dimensional axis of the container starting from said two or more acquired images;
A.2 positioning a three-dimensional model of the container stored in a memory unit on said at least one reference three-dimensional axis as determined in step A.1;
A.3 forming a planar image of said at least one portion of the side surface of the container, wherein each two-dimensional point (u, v) corresponds to a specific three-dimensional point (x, y, z) of the selected three-dimensional model in said two or more acquired images according to a mathematical correspondence indicative of a spatial positioning of said one or more cameras with respect to the container when the latter is positioned in said at least one optimal inspection position.
Always according to the invention, the rectification procedure may further comprise the following final step:
A.4 determining possible defects of said at least one portion of the side surface of the container, preferably of one or more labels applied thereon.
Still according to the invention, said three-dimensional model of the container may comprise at least one array of points belonging to at least one portion of an external surface of the container, preferably angularly equispaced and/or equispaced in height.
Furthermore according to the invention, the container may be a body of revolution, said at least one reference three-dimensional axis may be an axis of rotation of the container, and step A.1 may comprise the following substeps:
- for each one of said two or more acquired images, determining a container axis and determining a plane passing through an optical centre of the camera that has acquired the image under consideration on which this axis lays;
- determining said at least one reference three-dimensional axis as a best approximation among the planes so determined on the basis of said two or more acquired images, preferably as the straight line minimising the distance from the so determined planes;
where determination of the axis of the container in each one of said two or more acquired images is preferably carried out in one of the ways selected from the groups comprising:
- determining symmetrical contours of the container and determining a median line as axis,
- determining as axis an orthogonal line passing through a median point of a cap and/or of a neck and/or of a bottom of the container. Always according to the invention, the container may be a body not of revolution, and at least one of said two or more acquired images may be a, preferably top, plan image of the container.
Still according to the invention, the method may execute, preferably periodically, a calibration procedure comprising the following steps:
B.1 determining a spatial positioning of said one or more cameras with respect to the container when this is positioned in said at least one optimal inspection position;
B.2 obtaining said mathematical correspondence indicative of said spatial positioning.
Furthermore according to the invention, the method may execute a procedure of storing at least one two-dimensional shape of the container comprising the following steps:
C.1 determining at least one univocally defined reference three- dimensional axis of the container starting from said two or more acquired images;
C.2 storing said at least one two-dimensional shape related to said at least one reference three-dimensional axis;
the storing procedure further preferably comprising the following step: C.3 constructing and storing said three-dimensional model of the container,
the storing procedure further more preferably comprising the following step:
C.4 determining possible defects of the container.
Always according to the invention, the container may be a body of revolution, said at least one reference three-dimensional axis may be an axis of rotation of the container, and step C.1 may comprise the following substeps:
- for each one of said two or more acquired images, determining a container axis and determining a plane passing through an optical centre of the camera that has acquired the image under consideration on which this axis lays;
- determining said at least one reference three-dimensional axis as a best approximation among the planes so determined on the basis of said two or more acquired images, preferably as the straight line minimising the distance from the so determined planes;
where determination of the axis of the container in each one of said two or more acquired images is preferably carried out in one of the ways selected from the groups comprising:
- determining symmetrical contours of the container and determining a median line as axis,
- determining as axis an orthogonal line passing through a median point of a cap and/or of a neck and/or of a bottom of the container, and wherein step C.1 preferably determines a generating curve of said body that is preferably stored in step C.2.
Still according to the invention, the container may be a body not of revolution, and at least one of said two or more acquired images may be a, preferably top, plan image of the container.
Furthermore according to the invention, the method may further comprise the following preliminary steps:
D.1 determining when the container is in said at least one optimal inspection position; and
D.2 making said one or more cameras acquire said two or more images of the container.
It is also specific subject matter of this invention an automated apparatus of optical inspection of containers, in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, comprising an inspection chamber crossed by a conveyor belt and provided with one or more cameras controlled by a controlling and processing unit provided with a memory unit, said one or more cameras being capable to acquire two or more images of a container moved by the conveyor belt when the container is in an optimal inspection position within the inspection chamber, said two or more images being sent to the controlling and processing unit, the apparatus being characterised in that the controlling and processing unit is capable to execute the automated method of optical inspection of containers as previously described.
Always according to the invention, said cameras may be at least four, four cameras being preferably placed at the four vertices of a rectangle, more preferably pairwise opposed, still more preferably mounted on respective mechanical devices for adjusting height and, even more preferably, for adjusting orientation.
Still according to the invention, said one or more cameras may comprise at least one camera oriented according to an axis orthogonal to the plane of the conveyor belt, so as to acquire a, preferably top, plan image of the container.
Furthermore according to the invention, the apparatus may be further provided with detecting electronic means, connected to the controlling and processing unit, capable to detect when a container moved by the conveyor belt is in said optimal inspection position, said detecting electronic means preferably comprising a sensor, more preferably an optoelectronic sensor, connected to the controlling and processing unit and an encoder connected to the conveyor belt.
The present invention will be now described, by way of illustration and not by way of limitation, according to its preferred embodiments, by particularly referring to the Figures of the enclosed drawings, in which:
Figure 1 schematically shows a perspective view of a preferred embodiment of the apparatus according to the invention;
Figure 2 shows a top view of a portion of the apparatus of Figure 1; Figure 3 shows a perspective view of a sectioned portion of the apparatus of Figure 1;
Figure 4 shows a perspective view of a particular of the apparatus of Figure 1 ;
Figure 5 shows an example of acquired images from the cameras of the apparatus of Figure 1 during the calibration procedure; and
Figure 6 shows an example of acquired images from the cameras of the apparatus of Figure 1 during the procedure of storing the shape of a container.
In the Figures, identical reference numbers are used for alike elements.
With reference to Figures 1-4, it may be observed that a preferred embodiment of the apparatus 1 according to the invention comprises an inspection chamber of octagonal plan, accessible through a front hatch 2 and a rear hatch 3, which inspection chamber is crossed by a conveyor belt 4 for moving containers, such as bottles, bowls and vessels, to be inspected. As shown in particular in Figures 2 and 3, the conveyor belt 4 is flanked by side bars 15 at the inlet and outlet of the inspection chamber for guiding the containers.
Within the inspection chamber, a sensor 5, preferably an optoelectronic one, is located so as to detect when a container, represented in Figures 2 and 3 as a large bottle 6 or as a small bottle 6', that is moved by the conveyor belt 4, begins to occupy a central zone of the inspection chamber. Two interspaces are provided at the sides of the conveyor belt 4 which are of size sufficient to let containers 6" falling from the same belt pass. As it will be described later, the detection signal of the sensor 5 is used for determining when the container (6 or 6') is in an optimal position, preferably corresponding with the centre of the inspection chamber, wherein four cameras 7 simultaneously acquire respective images of the same container.
In particular, the four cameras 7 are preferably arranged at the four vertices of a rectangle, more preferably pairwise opposed, and they are housed in proper angular seats 8 accessible from outside by removing respective angular protective chassis 9.
As shown in Figure 4, each camera 7 is preferably mounted on a mechanical device 10 for adjusting height and, more preferably, adjusting orientation of the same camera 7. An inner wall 11 allows the objective only of the respective camera 7, sliding within a vertical slot 12 (depending on the height determined by the mechanical device 10), to be visible from inside the inspection chamber, as shown in Figures 3 and 4, in particular hiding the mechanical device 10.
The sensor 5 and the four cameras 7 are connected to a controlling and processing unit 13, provided with a monitor 14, preferably an adjustable one, for displaying the outcome of inspections.
In particular, when the sensor 5 detects the presence of a container (6 or 6') beginning to occupy a central zone of the inspection chamber, the unit 13 is capable to determine, on the basis of the signal coming from an encoder (not shown) connected to the conveyor belt 4 and also on the basis of the known size of the moved container (6 or 6'), the instant at which the container is in the optimal position, preferably corresponding with the centre of the inspection chamber, wherein the four cameras 7 simultaneously acquire respective images of the same container. When the container is in the aforementioned optimal position, the unit 13 controls the cameras 7 making them acquire simultaneous images of the container, which images are sent to the unit 13 for processing them in order to identify its possible defects.
The controlling and processing unit 13 executes an automated method of inspection, through a memorised software, as described in the following.
First of all, the method pr ovides for a preliminary procedure o f calibration of the set of cameras 7 for determining the spatial three- dimensional positioning of the cameras 7 within the inspection chamber.
One of the usable calibration techniques may be, by way of example, the technique described by Roger Y. Tsai in "A Versatile Camera Calibration Technique for High-Accuracy 3D Machine Vision Metrology Using Off-the-Shelf TV Cameras and Lenses", IEEE Journal of Robotics and Automation, Vol. RA-3, No. 4, August 1987. In this case, the calibration step provides to frame a same non-planar object of calibration simultaneously with all the cameras 7. Hence, each camera acquires a respective portion of the calibration object, obtaining four images as shown, for instance, in Figure 5. Some notable points are evident on this calibration object which have known position in terms of spatial coordinates (x, y, z). In the images acquired by each camera, the unit 13 identifies the coordinates of the notable points in terms of planar coordinates of the images (u, v), so as to determine for each camera the correspondences between the notable points (u, v) identified on the images and three-dimensional points (x, y, z). As a consequence, the unit 13 is capable to obtain a mathematical correspondence (given by a matrix of intrinsic and extrinsic parameters characteristic of each camera) between the three-dimensional points and the homologous two- dimensional points. At the end of the calibration step, the spatial position of the cameras 7 is known with respect to the calibration object and, consequently, within the inspection chamber.
In particular, the calibration procedure of the apparatus may be repeated whenever there occur setting and/or structural modifications.
During the automated inspection, when a container (6 or 6') is in the optimal position, the four cameras 7 acquire respective simultaneous images of the same container.
On the basis of such four simultaneous images the controlling and processing unit 13 is capable to execute a procedure for storing the shape of the same container, constructing a three-dimensional model of the container, provided that it is assimilable to a body of revolution. The so constructed three-dimensional model may be stored in the unit 13 or used for comparing it with a reference three-dimensional model previously stored in the unit 13 in order to determine possible defects of the same container (e.g., in case of bottles to inspect, for checking that the diameter of the bottles has an established size).
Such storing procedure comprises a step of identifying the three- dimensional rotation axis of the container starting from the identification of the axes in the two-dimensional acquired images. This allows to correct possible perspective errors present in the two-dimensional images acquired by the cameras. Afterwards, the unit 13 executes a step of identifying the contour of the container, or the generating curve of the three-dimensional model, as best approximation of the set of contours obtained in the two-dimensional images with respect to the previously identified three-dimensional axis.
In particular, identification of the three-dimensional axis of the container may comprise the following steps:
- for each two-dimensional image, determining the container axis as shown in Figure 6;
- for each two-dimensional image, determining the plane on which the container axis lays which plane passes through the optical centre of the camera that has acquired the two-dimensional image under consideration;
- determining the three-dimensional axis of the container as the best approximation among the planes so determined on the basis of the two-dimensional images (by way of example, the three-dimensional axis may be determined as the straight line minimising the distance from the so determined planes).
Determination of the container axis in each two-dimensional image may be carried out in several ways. By way of example, it is possible to determine on each two-dimensional image the left and right symmetrical edges of the container, and to determine the median line as two- dimensional axis. Alternatively, the container axis in each two-dimensional image could be determined as the orthogonal line passing through the median point of the cap and/or of the neck and/or of the bottom of the container.
On the basis of the four simultaneous images acquired by the cameras 7, the controlling and processing unit 13 is capable to execute a procedure of rectification onto the plane of the side surface of the container.
Such rectification procedure comprises a step of identifying the three-dimensional rotation axis of the container starting from identification of the axes in the acquired two-dimensional images, similarly to what previously seen for the procedure of storing the shape of the container.
Afterwards, the rectification procedure comprises a step of positioning the (known) three-dimensional model of the container on the three-dimensional axis so indentified for the container under examination.
In particular, such three-dimensional model is an array of points angularly equispaced and equispaced in height on the external surface of the container that is desired to rectify.
Finally, the rectification procedure comprises a step of forming a planar image of the external surface of the container, wherein for each three-dimensional point (x, y, z) of the three-dimensional model (previously positioned on the three-dimensional axis of the container under examination) it is formed the output rectified image by taking the corresponding two-dimensional point (u, v) (thanks to the mathematical correspondence identified in the calibration step) of the image of the camera closer to the same three-dimensional point (x, y, z). The image that is formed represents the external surface of the unrolled container.
Such rectified image of the external surface may be used by the unit 13 for determining possible defects, for instance, of one or more labels, e.g. thermal shrinking ones, applied on the external surface of the container under examination.
Other embodiments of the apparatus according to the invention also allow the inspection of containers not derived from bodies of revolution. In this case, the apparatus is advantageously provided with a further top camera (or bottom camera, if the conveyor belt is transparent) that acquires a top plan image (or a bottom plan image, if the conveyor belt is transparent) on the basis of which the controlling and processing unit 13 is capable to determine the container orientation on the basis of the known three-dimensional model (as polygonal mesh) of the same container. In this case, the unit 13 would determine the container orientation preferably on the basis of the recognition of a univocally defined reference axis of the three-dimensional model. Possibly, such three-dimensional model could be also directly obtained by the unit 13 on the basis of the images acquired by the cameras. Also such further camera undergoes a calibration procedure similarly to what seen above.
It must be understood that other embodiments of the apparatus according to the invention may be not provided with the sensor 5 for detecting the presence of the container. In this case, the controlling and processing unit 13 is capable, on the basis of a sequence of subsequent images acquires by the cameras, to determine which acquired images are the ones wherein the container is in the optimal (preferably central) position of inspection.
Moreover, the procedure for storing the shape of the containers is not an essential feature of the apparatus. In other words, the controlling and processing unit 13 may simply only execute the calibration procedure and the procedure of rectification onto the plane of the side surface of the containers. In this regard, also the calibration procedure could be made only once at the end of the apparatus assembly in the factory, whereby the controlling and processing unit 13 could then only execute the procedure of rectification onto the plane of the side surface of the containers. '
Finally, other embodiments of the apparatus according to the invention may comprise a number of cameras different from four. The essential feature is that the acquired images are sufficient to take the whole side surface (and, in case of bodies not of revolution, a plan view) of the container. To this end, the apparatus may be provided with a shooting system with cameras comprising at least one camera and provided with one or more mirrors and/or mechanical devices for moving said at least one camera and/or said one or more mirrors.
The present invention has been described, by way of illustration and not by way of limitation, according its preferred embodiments, but it should be understood that those skilled in the art can make variations and/or changes, without so departing from the related scope of protection, as defined by the enclosed claims.

Claims

1. Automated method of optical inspection of containers (6, 6'), in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, wherein one or more cameras (7) acquire two or more images of a container (6, 6') moved by a conveyor belt (4) when the container (6,
6') is in at least one optimal inspection position within an inspection chamber, the method being characterised in that it performs a procedure of rectification onto a plane of at least one portion of a side surface of the container (6, 6') on the basis of said two or more acquired images comprising the following steps:
A.1 determining at least one univocally defined reference three- dimensional axis of the container (6, 61) starting from said two or more acquired images;
A.2 positioning a three-dimensional model of the container (6, 6') stored in a memory unit on said at least one reference three-dimensional axis as determined in step A.1 ;
A.3 forming a planar image of said at least one portion of the side surface of the container (6, 6'), wherein each two-dimensional point (u, v) corresponds to a specific three-dimensional point (x, y, z) of the selected three-dimensional model in said two or more acquired images according to a mathematical correspondence indicative of a spatial positioning of said one or more cameras (7) with respect to the container (6, 6') when the latter is positioned in said at least one optimal inspection position.
2. Method according to claim 1 , characterised in that the rectification procedure further comprises the following final step:
A.4 determining possible defects of said at least one portion of the side surface of the container (6, 6'), preferably of one or more labels applied thereon.
3. Method according to claim 1 or 2, characterised in that said three-dimensional model of the container (6, 6') comprises at least one array of points belonging to at least one portion of an external surface of the container (6, 6'), preferably angularly equispaced and/or equispaced in height.
4. Method according to any one of the preceding claims, characterised in that the container (6, 6') is a body of revolution, in that said at least one reference three-dimensional axis is an axis of rotation of the container (6, 6'), and in that step A.1 comprises the following substeps:
- for each one of said two or more acquired images, determining a container axis and determining a plane passing through an optical centre of the camera that has acquired the image under consideration on which this axis lays;
- determining said at least one reference three-dimensional axis as a best approximation among the planes so determined on the basis of said two or more acquired images, preferably as the straight line minimising the distance from the so determined planes;
where determination of the axis of the container (6, 6') in each one of said two or more acquired images is preferably carried out in one of the ways selected from the groups comprising:
- determining symmetrical contours of the container (6, 6') and determining a median line as axis,
- determining as axis an orthogonal line passing through a median point of a cap and/or of a neck and/or of a bottom of the container (6, 6').
5. Method according to any one of claims 1 to 3, characterised in that the container (6, 6') is a body not of revolution, and in that at least one of said two or more acquired images is a, preferably top, plan image of the container (6, 6').
6. Method according to any one of the preceding claims, characterised in that it executes, preferably periodically, a calibration procedure comprising the following steps:
B.1 determining a spatial positioning of said one or more cameras (7) with respect to the container (6, 61) when this is positioned in said at least one optimal inspection position;
B.2 obtaining said mathematical correspondence indicative of said spatial positioning.
7. Method according to any one of the preceding claims, characterised in that it executes a procedure of storing at least one two- dimensional shape of the container (6, 6') comprising the following steps: C.1 determining at least one univocally defined reference three- dimensional axis of the container (6, 6') starting from said two or more acquired images;
C.2 storing said at least one two-dimensional shape related to said at least one reference three-dimensional axis;
the storing procedure further preferably comprising the following step: C.3 constructing and storing said three-dimensional model of the container (6, 6'),
the storing procedure further more preferably comprising the following step:
C.4 determining possible defects of the container (6, 6').
8. Method according to claim 7, characterised in that the container (6, 6') is a body of revolution, in that said at least one reference three- dimensional axis is an axis of rotation of the container (6, 6'), and in that step C.1 comprises the following substeps:
- for each one of said two or more acquired images, determining a container axis and determining a plane passing through an optical centre of the camera that has acquired the image under consideration on which this axis lays;
- determining said at least one reference three-dimensional axis as a best approximation among the planes so determined on the basis of said two or more acquired images, preferably as the straight line minimising the distance from the so determined planes;
where determination of the axis of the container (6, 61) in each one of said two or more acquired images is preferably carried out in one of the ways selected from the groups comprising:
- determining symmetrical contours of the container (6, 6') and determining a median line as axis,
- determining as axis an orthogonal line passing through a median point of a cap and/or of a neck and/or of a bottom of the container (6, 61),
and wherein step C.1 preferably determines a generating curve of said body that is preferably stored in step C.2.
9. Method according to claim 7, characterised in that the container
(6, 6') is a body not of revolution, and in that at least one of said two or more acquired images is a, preferably top, plan image of the container (6, 6').
10. Method according to any one of the preceding claims, characterised in that it further comprises the following preliminary steps:
D.1 determining when the container (6, 6') is in said at least one optimal inspection position; and D.2 making said one or more cameras (7) acquire said two or more images of the container (6, 6').
11. Automated apparatus (1) of optical inspection of containers (6, 6'), in particular of external side wall of bottles, bowls, and vessels intended to store powdered substances and/or gels and/or liquids, preferably food and beverages, comprising an inspection chamber crossed by a conveyor belt (4) and provided with one or more cameras (7) controlled by a controlling and processing unit (13) provided with a memory unit, said one or more cameras (7) being capable to acquire two or more images of a container (6, 6') moved by the conveyor belt (4) when the container (6, 6') is in an optimal inspection position within the inspection chamber, said two or more images being sent to the controlling and processing unit (13), the apparatus being characterised in that the controlling and processing unit (13) is capable to execute the automated method of optical inspection of containers (6, 6') according to any one of the preceding claims 1-9.
12. Apparatus (1) according to claim 11 , characterised in that said cameras (7) are at least four, four cameras (7) being preferably placed at the four vertices of a rectangle, more preferably pairwise opposed, still more preferably mounted on respective mechanical devices (10) for adjusting height and, even more preferably, for adjusting orientation.
13. Apparatus (1) according to claim 11 or 12, characterised in that said one or more cameras (7) comprise at least one camera oriented according to an axis orthogonal to the plane of the conveyor belt (4), so as to acquire a, preferably top, plan image of the container (6, 6').
14. Apparatus (1) according to any one of claims 11 to 13, characterised in that it is further provided with detecting electronic means (5), connected to the controlling and processing unit (13), capable to detect when a container (6, 6') moved by the conveyor belt (4) is in said optimal inspection position, the controlling and processing unit (13) being capable to execute the automated method of optical inspection of containers (6, 6') according to claim 10, said detecting electronic means (5) preferably comprising a sensor (5), more preferably an optoelectronic sensor, connected to the controlling and processing unit (13) and an encoder connected to the conveyor belt (4).
PCT/IT2010/000317 2009-07-31 2010-07-19 Automated apparatus of optical inspection of containers and related automated method of inspection WO2011013153A1 (en)

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ITRM2009A000409A IT1398364B1 (en) 2009-07-31 2009-07-31 AUTOMATIC OPTICAL CONTAINER INSPECTION SYSTEM AND ITS AUTOMATIC INSPECTION METHOD.
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