METHOD AND APPARATUS FOR CHECKING TYRES IN A PRODUCTION LINE

Abstract

A method and apparatus for checking tyres in a tyre production line. The method includes alternately illuminating, with a first and second grazing light radiation, a surface portion of the tyre and respectively acquiring a first and second two-dimensional digital image of the illuminated surface portion. For each point of the surface portion, the respective overall light power of the first and second light radiation incident at the point respectively comes from two half-spaces that are opposite with respect to an optical plane passing through the perpendicular to the surface at the point; and comparing the first and second image to obtain information on an altimetric profile of the surface portion.

Claims

1.-20. (canceled)

21. A method for checking tyres in a tyre production line, the method comprising: providing a tyre to be checked; illuminating, with a first grazing light radiation, a surface portion of said tyre and acquiring a first image of said surface portion illuminated by said first light radiation, said first image being two-dimensional; illuminating substantially said surface portion, at a time different from that when the surface portion is illuminated with the first radiation, with a second grazing light radiation and acquiring a second image of substantially said surface portion illuminated by said second light radiation, said second image being two-dimensional; wherein for each point of said surface portion, at least 75% of a respective overall light power of said first and second light radiation incident at the point respectively comes from two half-spaces that are opposite with respect to an optical plane passing through the perpendicular to the surface of the tyre at said each point; and processing said first and second image, wherein said first and second image are compared with each other in order to obtain information on an altimetric profile of said surface portion.

22. The method according to claim 21, wherein said comparison between the first and second image comprises calculating the difference between said first and second image.

23. The method according to claim 21, wherein said comparison between the first and second image comprises calculating a difference image in which each pixel is associated with a value representative of the difference between the values associated with the corresponding pixels in said first and second image.

24. The method according to claim 21, wherein said processing of said first and second image comprises detecting the possible presence of defects on the surface portion.

25. The method according to claim 21, wherein for each point of said surface portion, at least 90% of the respective overall light power of said first and second light radiation incident at the point respectively comes from said two opposite half-spaces.

26. The method according to claim 21, wherein at least 75% of the respective overall light power of said first and second light radiation incident on each point of said surface portion forms, with a plane tangent to the surface of said tyre at said each point, a first incidence angle with amplitude smaller than or equal to 55°.

27. The method according to claim 21, wherein at least 75% of the respective overall light power of said first and second light radiation incident on each point of said surface portion forms, with a plane tangent to the surface of said tyre at said each point, a first incidence angle having amplitude greater than or equal to 10°.

28. The method according to claim 21, wherein at least 75% of the respective overall light power of said first and second light radiation incident on each point of said surface portion forms, with a reference plane orthogonal to said optical plane at said each point and passing through the perpendicular to the surface at said each point, a second incidence angle smaller than or equal to 45°, in absolute value.

29. The method according to claim 21, comprising illuminating said surface portion, at a time different from those when the surface portion is illuminated with the first and second radiation, with a third light radiation different from the first and second radiation, and acquiring a third image of said surface portion illuminated by said third light radiation, said third image being two-dimensional and said third light radiation being diffuse.

30. The method according to claim 29, further comprising processing said third image in order to detect the possible presence of defects on the surface portion, said processing using the information obtained from the aforesaid comparison between the first and second image.

31. The method according to claim 21, wherein said first and second images are digital images that are composed of a respective plurality of first and second linear images of a succession of linear surface portions, contiguous or partially superimposed on each other, said first and second linear images being acquired on each linear portion of said succession of linear portions respectively illuminated by said first and second light radiation in an alternated sequence.

32. The method according to claim 31, wherein said third image is a digital image composed of a plurality of third linear images of said succession of linear surface portions, said third linear images being acquired on each linear portion of said succession of linear portions illuminated by said third light radiation, in a sequence alternating with said acquisition of said respective first and second linear images.

33. The method according to claim 31, wherein said succession of linear portions is obtained by rotation of the tyre around its axis.

34. The method according to claim 21, wherein before comparing the first and the second image with each other, provision is made for equalising said first and second image with respect to each other.

35. The method according to claim 21, wherein a time lag in the acquisition of two pixels belonging to each pair of corresponding pixels of the first and second image is less than 0.5 milliseconds.

36. An apparatus for checking tyres in a tyre production line comprising: a support for a tyre; a first light source and a second light source adapted to respectively emit a first and a second light radiation for illuminating substantially a same surface portion of said tyre and a detection system adapted to acquire a first and second image of substantially said surface portion illuminated respectively by said first and second light radiation, said first and second image being two-dimensional images; a command and control unit configured for: alternately activating said first light source and second light source, and activating said detection system in order to acquire said first and second image synchronously with the activation of the first and second source, respectively; a processing unit configured for the following functions: receiving, from the detection system, said first and second digital image; and processing said first and second image, wherein said first and second image are compared with each other in order to obtain information on an altimetric profile of said surface portion; wherein: said first light radiation and said second light radiation are grazing; and for each point of said surface portion, at least 75% of the respective overall light power of said first and second light radiation incident at the point respectively comes from two half-spaces that are opposite with respect to an optical plane passing through the perpendicular to the surface of the tyre at said each point.

37. The apparatus according to claim 36, comprising a third light source adapted to emit a third light radiation for illuminating said surface portion, wherein said detection system is adapted to acquire said third image and wherein said command and control unit is configured for activating said third light source at a time different from those when the surface portion is illuminated with the first and second radiation, and driving said detection system in order to acquire said third image synchronously with the activation of the third source.

38. The apparatus according claim 36, wherein the detection system comprises a linear camera having an objective line.

39. The apparatus according claim 36, wherein the apparatus comprises a system for detecting the angular position of said support, the command and control unit being configured for activating said first light source, second light source, and third light source and driving said detection system as a function of a signal of angular position of the support sent by said angular position detection system.

40. The apparatus according claim 36, comprising a movement member adapted to rotate said support, and hence the tyre, around a rotation axis thereof, the command and control unit being configured for driving said movement member.

Description

[0078] Further characteristics and advantages will be clearer from the detailed description of several exemplary but non-exclusive embodiments of a method and an apparatus for checking tyres in a tyre production line, in accordance with the present invention. Such description will be set forth hereinbelow with reference to the set of figures, provided only as a non-limiting example, in which:

[0079] FIG. 1 shows a partial and schematic perspective view, partially in cross section and partially in terms of functional blocks, of an apparatus for checking tyres in accordance with a first embodiment of the present invention;

[0080] FIG. 2 shows a partial and schematic perspective view of a detail of FIG. 1;

[0081] FIG. 2a shows an enlarged detail of FIG. 2;

[0082] FIG. 3 shows a partial and schematic perspective view of an apparatus for checking tyres in accordance with a second embodiment of the present invention;

[0083] FIGS. 4a and 4b schematically show an image of a tyre surface portion illuminated respectively with right and left grazing light;

[0084] FIG. 4c schematically shows an image obtained via comparison of the images 4a and 4b.

[0085] With reference to the figures, reference number 1 generally indicates an apparatus for checking tyres in a tyre production line according to the present invention. Generally, the same reference number will be used for possible variants of similar elements.

[0086] The apparatus 1 comprises a support 102 adapted to support the tyre 200 on one sidewall and to rotate the same around its rotation axis 201, typically arranged according to the vertical. The support 102 is typically actuated by a movement member that is not further described and illustrated, since it can as an example be of known type. The support for the tyre may possibly be configured for blocking the same, for example the respective abutted bead.

[0087] Preferably a detection system 104 is comprised, comprising a linear camera 105 having an objective line 106 lying on an optical plane 107 passing through the linear camera. The present invention also contemplates the alternative case in which the camera is a matrix camera (‘area camera’). In such case, also the illuminated and acquired surface portion is matrix.

[0088] The apparatus comprises a first light source 108, a second light source 109 and a third light source 110 adapted to respectively emit a first, a second and a third light radiation for illuminating a linear surface portion 202 of said tyre coinciding with the objective line (e.g. when the surface portion is planar) or in proximity to the objective line (due to the curvilinear progression of the surface of the tyre), as shown in FIGS. 1 and 2, 2a.

[0089] The detection system is adapted to acquire a respective two-dimensional digital image of the linear surface portion illuminated by at least one from among the first, second and third light radiation.

[0090] Typically the apparatus comprises a robotic arm (not shown) on which said first light source, second light source and third light source and the detection system are mounted. Preferably the first light source 108 and the second light source 109 are each constituted by a single respective sub-source 111 and 112.

[0091] Preferably the third light source 110 is constituted by four respective sub-sources 113 distributed on both sides of the optical plane 107 and symmetrically with respect to such plane.

[0092] Each sub-source 111-113 has a respective main extension direction (indicated as an example with the dashed lines 114 in FIG. 2a) which is extended parallel to the optical plane 107 and hence to the objective line 106.

[0093] Each sub-source typically comprises a plurality of LED sources arranged aligned along the main extension direction.

[0094] In the enclosed figures, the sub-light sources are schematically shown with reference to their respective emitting surface (in the figures, as an example with rectangular shape), which for example can coincide with a transparent protection glass and/or diffuser.

[0095] As an example, the sub-sources have a size along the main extension direction 114 equal to 10 cm for the embodiment shown in FIGS. 2 and 6 cm for the embodiment shown in FIG. 3, and a size along the direction orthogonal to the main extension direction equal to about 1 cm.

[0096] Preferably the sub-sources 111 and 112 respectively lie on opposite sides with respect to the optical plane and are equidistant therefrom.

[0097] Preferably the distance of the sub-sources 113 of the third light source from the optical plane 107 is less than the distance between each sub-source of said first light source and second light source and the optical plane.

[0098] Preferably the sub-sources of the first light source, second light source and third light source are arranged in a manner such that for their entire extension they are superimposed in a view orthogonal to the objective line. As an example all the first and second ends, with respect to the main extension direction, lie on a respective plane orthogonal to the objective line.

[0099] In one embodiment, as shown as an example in FIGS. 1 and 2, 2a, the sub-sources of the first light source, second light source and third light source are arranged along a line (indicated with the number 115 in FIG. 2) on a reference plane 116 orthogonal to the objective line, line 115 being shaped as an arc of a circle with centre on the objective line (i.e. the sub-sources are equidistant from the objective line).

[0100] In an alternative embodiment, as shown in FIG. 3, the sub-sources are arranged along an angle line (indicated with the number 116 in FIG. 3) on the reference plane 116, with vertex on the optical plane 107.

[0101] As an example, for each point P (as an example indicated at one end in FIGS. 2 and 2a) of the objective line, a respective angle 120 (in FIG. 2a, shown with reference to a sub-source 113) having vertex at the point P and lying in a plane orthogonal to the objective line, and subtended by each of the sub-sources is equal to 6°.

[0102] As an example, taking a focal plane 121 orthogonal to the optical plane and passing through the objective line 106, the respective maximum angle 122 and 123 among all the angles formed between the focal plane and the planes passing through the objective line and all the points respectively of the first light source 108 and the second light source 109 (respectively of the sub-sources 111 and 112) is equal to 48°.

[0103] As an example, the respective minimum angle 124 and 125 among all the angles formed between the focal plane and the planes passing through the objective line and all the points respectively of the first light source and the second light source is equal to 42°.

[0104] Preferably the third light source 110 is adapted for illuminating the objective line with diffuse light.

[0105] As an example, a respective angle 126 having vertex at each point P of the objective line and lying in a plane orthogonal to the objective line, and subtended by the third light source, is equal to about 80°. In such a manner, a wide solid angle of the diffuse light is obtained.

[0106] As an example, a respective angle having vertex at each point P of the objective line and lying in the aforesaid orthogonal plane, and subtended by the set of the first light source, the second light source and the third light source, is equal to 96°.

[0107] In one embodiment of the apparatus particularly suitable for inspecting the internal surface of the tyre, as an example shown in FIG. 3, the detection system comprises a mirror 150 (also typically mounted on the robotic arm) having flat reflective surface arranged at the third light source perpendicular to the optical plane and intersecting the latter (typically on the median line of the mirror) in a manner so as to reflect the objective line in the optical plane by an angle as an example equal to 90°.

[0108] Preferably a command and control unit 140 is comprised that is configured for: [0109] selectively activating one or more of said first light source, second light source and third light source; [0110] activating the linear camera in order to acquire a respective two-dimensional digital image (colour or monochromatic) of the linear surface portion synchronously with the activation of one or more of said first light source, second light source and third light source.

[0111] The command and control unit is typically configured for also driving the movement member of the support 102. In such a manner, there is the succession of linear surface portions at the objective line of the linear camera, which can remain fixed.

[0112] Preferably the apparatus comprises an encoder (not shown) for detecting the angular position of the support, the command and control unit being configured for activating said first light source, second light source, and preferably third light source and driving the detection system as a function of a signal of angular position of the support sent by the encoder.

[0113] Preferably the command and control unit 140 is configured for: [0114] activating in alternated sequence said first light source, second light source and third light source; [0115] driving the linear camera in order to acquire respectively a first, second and third image synchronously with the activation of the first light source, the second light source and the third light source, respectively. In such a manner it is possible to acquire both an image in diffuse light and two images in grazing light.

[0116] Preferably a processing unit (e.g. integrated in the command and control unit 140) is comprised, configured for the following functions: [0117] receiving the acquired images from the linear camera; [0118] processing the images in order to check the surface portion.

[0119] Preferably the processing unit is configured for calculating the difference between the first and second image in order to obtain information on an altimetric profile (e.g. possible presence or lack of reliefs and/or depressions) of the linear surface portion.

[0120] Preferably, calculating the difference between the first and second image comprises calculating a difference image in which each pixel is associated with a value representative of the difference between the values associated with the corresponding pixels in the first and second image. In such a manner, it is possible to use the image obtained from the difference between the first and second image in order to indicate the three-dimensional elements (such as the pitting in relief on the internal surface of the tyre or the writing in relief) and keep such information under consideration in processing the image in diffuse light in order to search for defects.

[0121] A method for checking the surface of tyres in a tyre production line, as an example implemented by means of the aforesaid apparatus, is described hereinbelow.

[0122] First of all, a tyre 200 to be checked, for example abutted against a sidewall above the support 102, is arranged.

[0123] The command and control unit 140 drives the robotic arm in order to move the light sources close to the (external or internal) surface of the tyre, in a manner such that a linear surface portion at least partially coincides with, or is in proximity to, the objective line.

[0124] Then, the command and control unit drives the movement member of the support 102 in order to rotate the tyre.

[0125] As a function of the signal of angular position received by the encoder, with the rotation of the tyre underway, the command and control unit cyclically activates, in rapid alternated sequence, said first light source, second light source and third light source and activates the linear camera in order to acquire a respective two-dimensional digital image (colour or monochromatic) of the respective linear surface portion synchronously with the activation of the first light source, the second light source and the third light source, respectively. As an example, each single digital image of a linear portion comprises 1×2048 pixels in case of monochromatic camera, or 2×2048 pixels in the case of bilinear or RGB colour camera. As an example, the time lag between the acquisition of the first and second linear image, as well as between the second and third linear image and then cyclically between the first and third linear image, is less than 0.2 milliseconds.

[0126] After having executed the desired rotation of the tyre for sounding the desired surface portion, preferably at least one complete rotation in order to acquire the entire circular extension, a single digital image is obtained that is achieved with all the digital images of the sequence of linear portions, each illuminated with a respective light source. The processing unit receives such image from the detection system and separates the corresponding first, second and third image of the entire desired surface portion.

[0127] Such images are substantially superimposable pixel-by-pixel, even if the actual linear surface portion associated with a single linear image does not exactly coincide for the three images, due to the rotation of the tyre that in the meantime took place. Nevertheless, the selection of the acquisition frequency of the images and of the rotation speed is such that the three images are interlaced with each other and hence can be compared pixel-by-pixel. Advantageously, each pixel of the first (or second or third) image shows a micro-surface portion which is separated from the micro-surface portion shown by the pixel of the second (or respectively third or first) image corresponding to said each pixel, except for the linear surface size associated with a pixel, as an example the spatial gap being equal to about a third of a pixel. In such a manner, the three images are interlaced with each other and the acquisition of the three linear images occurs in a time interval during which the tyre has rotated a section equal to one pixel (as an example equal to 0.1 mm).

[0128] As stated, for each point of each linear surface portion, and hence for each point of the sounded surface portion, at least 75% of, as an example all of, the respective overall light power of the first and second light radiation incident at the point respectively comes from two half-spaces that are opposite with respect to the optical plane 107.

[0129] In addition, for each point of each linear surface portion at least 75% of the, as an example all the, respective overall light power of the first and second light radiation incident on the point forms, with the plane tangent to the surface at the point (i.e. the focal plane 121), an incidence maximum angle 122 and 123 equal to about 48° (grazing light).

[0130] Preferably all the respective overall light power of the first, second and third light radiation incident on each point of the surface portion (or objective line) forms, with a reference plane 116 orthogonal to the optical plane and passing through the perpendicular to the surface at the point, an incidence angle smaller than or equal to 45°, in absolute value. For example, the angle 127 having vertex at any point (indicated as an example with P′ in FIG. 2a) of the objective line, lying in any one plane passing through the objective line and through the first light source and the second light source or the third light source, and subtended by the first light source, by the second light source or by the third light source, respectively, is equal to 60°. In such a manner, advantageously, each sub-source emits a directional light radiation incident on the objective line.

[0131] Preferably the processing unit processes the first and second image, comparing them with each other in order to obtain information on an altimetric profile of the surface portion.

[0132] Preferably the comparison between the first and second image comprises calculating a difference image in which each pixel is associated with a value representative of the difference between the values associated with the corresponding pixels in the first and second image.

[0133] Preferably, before comparing the first and second image with each other, provision is made for equalising the first and second image with respect to each other, for example by equalising the average brightness thereof overall or locally.

[0134] Preferably the processing unit processes the third image in diffuse light in order to detect the possible presence of defects on the surface portion, using the information obtained from the aforesaid comparison between the first and second image.

[0135] FIGS. 4a and 4b schematically show an embodiment respectively of a first and second image of a surface portion of tyre 200 comprising an element in relief 203 and an element without reliefs, or two-dimensional element, 204 (such as a release agent stain).

[0136] In FIG. 4a, where the image is obtained with grazing light from the right of the figure, the image comprises a shade zone 205 projected towards the left by the element 203; in FIG. 4b, where the image is obtained with grazing light from the left of the figure, the image comprises a shade zone 206 projected towards the right by the same 203. It is observed that the element 204 is instead acquired substantially in an identical manner in the two images, since it equally meets the right and left grazing illuminations.

[0137] FIG. 4c schematically shows a difference image obtained by associating each pixel with the difference, in absolute value, between the values of the two images of FIGS. 4a and 4b. As can be seen, at the two-dimensional stain 204, the difference image does not have any brightness variation, while at the element in relief 203 (marked with shading in FIG. 4c) there is a considerable brightness variation, marking the presence of the element itself 203.