Calibration Tools and Methods

Abstract

The present invention relates to a calibration tool and method for calibrating a laser triangulation system, wherein the calibration tool comprises a tool body defining a reference plane, which can rotate relative to a measurement system around a rotation axis perpendicular to the reference plane, wherein the tool body is provided with one or more calibration surfaces, the calibration surfaces defining a pattern of calibration positions, wherein the pattern comprises at least three columns extending in a radial direction away from the rotation axis and at least three rows extending circumferentially around the rotation axis, wherein, for each column, the height of the calibration position in the corresponding column varies relative to the reference plane in a height direction perpendicular to the reference plane, and wherein, for each row, the height of the calibration position in the corresponding row varies relative to the reference plane in a height direction.

Description

Technical Field

[0001] The present invention relates to a calibration tool and method for calibrating a measurement system, in particular a laser triangulation system. Background Art

[0002] In the field of tire building, measurement systems are used during various stages of production to measure the quality and / or characteristics of one or more tire components. One such stage is the production of the bead-apex. The bead-apex is formed by subsequently applying a bead and an apex around the perimeter of a bead-apex drum. The bead-apex drum can receive beads and apexes of various shapes and sizes. In addition, the bead-apex drum also has various shapes and sizes and can be replaced by another bead-apex drum where appropriate. Finally, the part of the bead-apex drum that supports the apex is typically tapered to support the apex at an inclination angle relative to the radial direction. Summary of the Invention

[0003] A disadvantage of known laser triangulation systems is that they can become inaccurate over time. It is known to calibrate a laser triangulation system by measuring a stationary object having a predetermined size and comparing the measured value with the predetermined size. However, this calibration process provides only a limited amount of feedback based on the size of the stationary object. Although the measurement system can be properly calibrated for the size of the stationary object, measurements in other size ranges remain uncalibrated and may be inaccurate.

[0004] It is an object of the present invention to provide a calibration tool and a method for calibrating a measurement system, in particular a laser triangulation system, wherein the calibration can be improved.

[0005] According to a first aspect, the present invention provides a calibration tool for calibrating a laser triangulation system, wherein the calibration tool includes a tool body rotatable about a rotation axis perpendicular to a reference plane relative to the measurement system, wherein the tool body is provided with one or more calibration surfaces that define a pattern of calibration positions, in particular a radial grid, wherein the pattern includes at least three columns extending radially away from the rotation axis and at least three rows extending circumferentially around the rotation axis, wherein for each column, the height of the calibration positions within the respective column varies in a height direction perpendicular to the reference plane, and wherein for each row, the height of the calibration positions within the respective row varies in the height direction relative to the reference plane.

[0006] The tool body can be conveniently rotated relative to the measuring system in the same manner as the bead - apex roller. By rotating the tool body, the columns can be positioned one after another in the measuring position to measure the calibration positions within each column by means of the measuring system. In particular, the measuring system can project a laser line onto the tool body radially or parallel to the radial direction so that all the calibration positions in each column can be measured simultaneously along the same projected laser line. Each column of calibration positions represents or forms a specific height profile that can be used for calibrating the measuring system. Since the heights of the calibration positions vary both in the columns and rows, the measured values can be calibrated for a large number of calibration positions, thus providing a relatively large amount of feedback for the measuring system for various height positions.

[0007] Preferably, for each column, at least half of the calibration positions and preferably all the calibration positions within the corresponding column have different heights in the height direction relative to the reference plane. Thus, at least half of the calibration positions within the corresponding column generate unique calibration information for calibrating the measuring system.

[0008] In one embodiment, for each column, the heights of the calibration positions within the corresponding column relative to the reference plane decrease successively in the radial direction away from the axis of rotation. The successive decrease in height can be similar to or represent the decreasing height of the bead - apex supported on the bead - apex roller and thus can provide useful calibration information for calibrating the measuring system.

[0009] Preferably, the successive decrease in height has a constant decrement relative to the reference plane. Thus, the calibration information generated by the calibration positions within the corresponding column can be used to determine the scale of the measuring system, particularly the scale for converting pixels to actual units (i.e., millimeters). Alternatively, the successive decrease in height follows a certain curvature. Since a camera is used in the measuring system, the curvature can be selected, for example, to match or correct a specific lens distortion effect.

[0010] Additionally or alternatively, for each row, at least half of the calibration positions and preferably all the calibration positions within the corresponding row have different heights in the height direction relative to the reference plane. Thus, at least half of the calibration positions within the corresponding row generate unique calibration information for calibrating the measuring system.

[0011] In one embodiment, for each row, the heights of the calibration positions within the corresponding row relative to the reference plane increase successively in the circumferential direction. Thus, the calibration positions within the corresponding row can represent the various heights of different bead - apexes supported on the bead - apex roller at the radial position of the corresponding row. When combined with the successive decrease in height in the radial direction within the columns, a pattern of several columns with radially decreasing calibration positions can be formed, where the height of each column increases jointly with each row in the circumferential direction.

[0012] Preferably, the successive increases in height have a constant increment with respect to the reference plane. Thus, the calibration information generated by the calibration positions within the respective rows can be used to determine the scale of the measurement system, in particular the scale for converting pixels into physical units (i.e., millimeters).

[0013] In one embodiment, the height of each calibration position within the pattern with respect to the reference plane in the height direction is different from the height of the other calibration positions within the same column and the same row with respect to the reference plane. Thus, each calibration position within the pattern generates unique calibration information for the calibration of the measurement system.

[0014] Those skilled in the art will understand that the calibration tool according to the present invention may include only a single calibration surface in each column, each row, or the entire pattern. Such a single calibration surface may, for example, have a height that decreases gradually in the radial direction and a height that slopes gradually in the circumferential direction. Then, the measurement system will be configured to make measurements at certain positions on the single calibration surface, the positions corresponding to the calibration positions. The single calibration surface may hold an infinite number of calibration positions.

[0015] Conversely, in the embodiment shown in the drawings, for each column, one or more calibration surfaces include separate calibration surfaces for each calibration position within the respective column. By having different, separate calibration surfaces, the calibration positions are not easily confused and can be easily identified by the measurement system, i.e., by detecting the transition from one calibration surface to another.

[0016] Preferably, for each column, the tool body is provided with recesses extending between the respective calibration surfaces within the respective column to radially separate the respective calibration surfaces. By separating the columns, the calibration positions are even less likely to be confused. In addition, the presence of the recesses between the calibration surfaces allows for the measurement of distinct edges and / or base level or zero level measurements in the recesses.

[0017] More preferably, each calibration surface within the respective column defines a calibration edge at each transition from the respective calibration surface to an adjacent one in the recess, wherein at least one calibration position is located at one of the calibration edges. The calibration edges can be easily detected and / or measured and can thus serve as excellent calibration positions.

[0018] In a further embodiment, for each column, the calibration surfaces within the respective column extend in a common plane, wherein the common plane extends at an inclined angle with respect to the reference plane. The inclined common plane is similar to or represents the inclined, descending surface or conical surface of the bead - apex strip supported on the bead - apex strip drum. An additional advantage of the common plane is that all calibration positions are also located in the same common plane.

[0019] Additionally or alternatively, for each row, the one or more calibration surfaces comprise a separate calibration surface for each calibration position within the respective row. By having different, separate calibration surfaces, the calibration positions are not easily confused and can be easily identified by the measurement system, i.e. by detecting the transition from one calibration surface to another.

[0020] Preferably, for each row, the calibration surfaces within the respective row are stepped in height direction from one calibration surface to the next in the circumferential direction. The stepped height from one calibration surface to the next means that for each subsequent column its calibration surface can be easily distinguished from the calibration surface of the preceding column in the circumferential direction of the respective row. Furthermore, the height of each calibration surface may be constant in the circumferential direction between the steps so that a representative measurement of the respective calibration position may be made at any position in the circumferential direction between the steps. The accuracy of the rotational positioning of the calibration tool relative to the measuring system is therefore less important.

[0021] In another embodiment, the pattern comprises at least five columns, preferably at least eight columns. Additionally or alternatively, the pattern comprises at least four rows, preferably at least five rows. The number of columns determines the number of height profiles that can be calibrated. The number of rows determines the number of calibration positions within each column, ie within each height profile.

[0022] In a further embodiment, the tool body extends only over a portion of the entire circumference around the axis of rotation. Preferably, the tool body is formed as a circular segment. When the tool body is not a complete circle or ring, the tool body may be relatively compact, ie relatively compact compared to a bead-apex roller.

[0023] According to a second aspect, the present invention provides a method for calibrating a laser triangulation system using a calibration tool according to any of the preceding embodiments, wherein the laser triangulation system comprises a laser and a camera with a certain field of view, wherein the method comprises the following steps:

[0024] a) providing the calibration tool at least partially within the field of view of the camera;

[0025] b) projecting a laser line onto the calibration tool using the laser triangulation system;

[0026] c) rotating the calibration tool about a rotation axis so that the laser line is projected onto all calibration positions in a respective one of the columns; and

[0027] d) capturing with the camera an image of the laser line projected on all calibration positions in the corresponding column.

[0028] This method relates to the actual implementation of the calibration tool according to the first aspect of the present invention and thus has the same technical advantages, which will not be repeated hereinafter.

[0029] In a preferred embodiment of this method, step d) includes the following steps: repeating steps c) and d) for another column or all other columns. Thus, more or all of the calibration positions can be measured to have the maximum number of calibration data.

[0030] In a further embodiment of this method, the height of the calibration position of each column relative to the reference plane is predetermined, and wherein the method further includes the following steps: calibrating the laser triangulation system by associating the pixels in each captured image corresponding to the calibration position of the corresponding column with the calibration position within the corresponding column. This association can produce a scale for each calibration position that converts the pixels into actual units, i.e., micrometers, millimeters, or centimeters.

[0031] In a further embodiment, the method further includes the following steps:

[0032] f) Before or after steps a) to e), providing an empty bead - apex strip drum relative to the laser triangulation system, wherein the bead - apex strip drum has a reference plane and a base profile for supporting the bead - apex strip relative to the reference plane, and wherein the empty bead - apex strip drum is arranged such that its reference plane is in the same position as the reference plane of the calibration tool;

[0033] g) Projecting a laser line onto the empty bead - apex strip drum with the laser triangulation system;

[0034] h) Capturing an image of the laser line projected onto the empty bead - apex strip drum; and

[0035] i) Determining the base profile of the empty bead - apex strip drum relative to the reference plane of the empty bead - apex strip drum.

[0036] During the production of the bead - apex strip, the base profile of the bead - apex strip drum is covered by the bead - apex strip currently supported on the bead - apex strip drum. Although the height of the bead - apex strip relative to the reference plane can be measured, this measured value does not indicate the actual height of the bead - apex strip relative to the bead - apex strip drum. Therefore, when determining the base profile before production, i.e., when the bead - apex strip drum is still empty, the measuring system has more information from which the actual height of the bead - apex strip relative to the bead - apex strip drum can be determined.

[0037] Preferably, the method further includes the following steps:

[0038] j) Provide a bead - apex strip on the bead - apex strip roller;

[0039] k) Measure the bead - apex strip using the measurement system; and

[0040] l) Subtract the base profile of the empty bead - apex strip roller determined in step i) from the measured value.

[0041] The result after subtraction can represent the actual height of the bead - apex strip relative to the bead - apex strip roller.

[0042] According to a third aspect, the present invention provides a laser triangulation measurement system, comprising a laser, a camera, and a support for supporting the laser and the camera, wherein the measurement system further comprises a roller rotatable about a rotation axis for guiding a strip through the measurement system and a calibration tool for calibrating the measurement system, wherein the support is pivotable about a pivot axis between an operating position and a calibration position, in the operating position, the camera and the laser are directed towards the roller to measure the strip on the roller, and in the calibration position, the laser and the camera are directed towards the calibration tool.

[0043] Since the laser and the camera are supported on the same or a common support, they can be pivoted together easily and quickly, i.e., during a short interruption in the production process of the strip or even during the production process, between the corresponding positions. Since the calibration position is different from the operating position, calibration can be performed offline.

[0044] Preferably, the pivot axis is parallel to the rotation axis.

[0045] In a further embodiment, the support is arranged to pivot about the pivot axis between the operating position and the calibration position by at least forty - five degrees, and preferably by at least sixty degrees. Thus, the two positions can be sufficiently separated to prevent interference of the calibration tool with the production process at the operating position.

[0046] In another embodiment, the camera has an optical axis, wherein when the support is in the calibration position, the calibration tool defines a reference plane perpendicular to the optical axis of the camera. Thus, the camera can be positioned directly above the calibration tool to capture the best image of the laser line projected on the calibration tool.

[0047] In another embodiment, the drum includes a circumferential surface that supports the strip at a zero level relative to the camera, wherein the calibration tool includes one or more first calibration surfaces at a predetermined height relative to the reference plane in a height direction perpendicular to the reference plane for calibrating the zero level. The calibrated zero level can be used to determine the height of the strip under test above the calibrated zero level.

[0048] In another embodiment, the laser is arranged to project a laser line onto the calibration tool in a lateral direction parallel to the rotational axis of the drum, wherein the calibration tool includes one or more second calibration surfaces, the height of the one or more second calibration surfaces varying in the lateral direction relative to the reference plane in a height direction perpendicular to the reference plane. Thus, along a single laser line, several heights corresponding to different second calibration surfaces can be detected. Measurement data regarding the height of the second calibration surface can be used to determine the scale of the measurement system, in particular the scale for converting and / or correlating pixels in an image with actual units, i.e., microns, millimeters, or centimeters.

[0049] Preferably, the height of the one or more second calibration surfaces varies in the lateral direction according to a pattern that repeats at least twice, preferably at least three times, in the lateral direction. By repeating the pattern, the camera can be calibrated relative to more positions in the lateral direction, i.e., across most of the camera's field of view in the lateral direction.

[0050] According to a fourth aspect, the present invention provides a strip for clamping a tire component to a drum, wherein the strip is provided with a verification element for verifying a measurement system.

[0051] The strip can be mounted at a predetermined position on an empty drum (i.e., with no tire component clamped to the drum). At the predetermined position, the measurement system associated with the drum can measure the strip including the verification element to verify whether the previously calibrated measurement system still meets the requirements. In particular, the verification element can have a known or predetermined pattern, shape, or size to check whether the measured values still correspond to the known or predetermined pattern, shape, or size. Since during the clamping of the tire component, the strip can be mounted on the drum at a position substantially corresponding to its operating position on the drum. Thus, the verification can be performed online (i.e., at the same position where the strip is normally mounted).

[0052] In a preferred embodiment, the strip has a clamping side and a non-clamping side, the clamping side facing the tire component during clamping, and the non-clamping side being opposite to the clamping side, wherein the verification element is provided on the non-clamping side. Thus, the verification element can be easily observed from the outside when the strip is clamped to the drum.

[0053] In a further embodiment, the clamping strip has a longitudinal direction, and the verification element is arranged at or near one end of the clamping strip along the longitudinal direction. By arranging the verification element at or near one end of the clamping strip, the verification element is easily visible even if the clamping strip is covered in the central region for some reason.

[0054] In a further embodiment, the verification element is a slot. The characteristics of such a slot can be easily captured using a camera and laser triangulation.

[0055] According to a fifth aspect, the present invention provides a first cover plate that covers an intermediate space between two drum sections of a tire building drum, wherein the first cover plate includes one or more verification elements for verifying measurement values of a measurement system.

[0056] After initial calibration, i.e., when the measurement system has been calibrated using one or more calibration elements and / or tools, the verification elements on the first cover plate can be used to verify the measurement system. The verification elements are arranged on the drum and can be detected when the verification elements are not covered by a tire component. Since the verification elements are provided on a part of the drum that is also visible during the operation of the drum, the first cover plate can be verified online, i.e., at the same position where the cover plate is located during production.

[0057] According to a sixth aspect, the present invention provides a tire building drum including one or more first cover plates according to the fifth aspect of the present invention, wherein the tire building drum is rotatable about a rotational axis extending axially, wherein the tire building drum further includes one or more second cover plates, wherein each second cover plate includes a plurality of calibration elements arranged in a calibration pattern, and wherein the verification elements of the one or more first cover plates are axially in different positions relative to the plurality of calibration elements in the one or more second cover plates. By having the verification elements and the calibration elements in different positions, different values can be used to verify the measurement system to determine whether the ratio determined during calibration is correctly interpolated to the value expected by the verification elements.

[0058] The tire building drum has the same advantages as the first cover plate according to the fifth aspect of the present invention. In particular, since the verification elements and the calibration elements are in different positions, they can be used to verify the calibration.

[0059] Preferably, the first cover plate has a longitudinal direction, wherein the measuring system includes one or more cameras arranged side by side for respectively observing a first end portion, a second end portion, and a central portion of the first cover plate arranged side by side in the longitudinal direction, wherein the one or more verification elements include one or more verification elements at the first end portion, one or more verification elements at the second end portion, and one or more verification elements at the central portion. Thus, one or more cameras can be calibrated by capturing images of the verification elements in the corresponding portions. Preferably, each portion of the one or more verification elements includes a set of two or more verification elements, and more preferably, each portion includes three or more verification elements. Most preferably, three or more verification elements in each group form the same pattern for each group. Thus, each camera can be calibrated with substantially the same pattern.

[0060] According to a seventh aspect, the present invention provides a verification tool for verifying measured values of a measuring system for measuring one or more tire components applied around a tire building drum, wherein the verification tool includes an annular body circumferentially extending around a central axis and one or more reference elements provided on the annular body and representing characteristics of the one or more tire components, wherein the verification tool is provided with a central reference for determining the center of the verification tool in an axial direction parallel to the central axis.

[0061] The verification tool may generally correspond to the verification tool disclosed in WO 2016 / 122311 A1, which is incorporated herein by reference. There may be a slight error in the position of the verification tool on or along the tire building drum. This can be compensated as long as the center of the verification tool is known. Once the center is determined, the tire building drum with the verification tool around or beside it can be moved axially until the verification tool is in the position where the tire building drum usually is during operation relative to the measuring system. Alternatively, the measuring system can shift the measured values slightly to compensate for any deviation of the center of the verification tool relative to the measuring system.

[0062] Preferably, the verification tool is provided with one or more side references for determining one or more sides of the verification tool in the axial direction. The side can represent the side of the tire building drum.

[0063] More preferably, the central reference and the one or more side references are arranged collinearly in the axial direction. Thus, the central reference and the one or more side references can be measured simultaneously, i.e., by projecting a laser line on all the references.

[0064] According to an eighth aspect, the present invention provides a calibration tool for calibrating a measurement system, wherein the calibration tool includes a calibration section with one or more calibration elements and a verification section with one or more verification elements, wherein the calibration tool is invertible between a calibration position and a verification position about an inversion axis, and wherein when inverted about the inversion axis, the calibration section and the verification section exchange positions.

[0065] Thus, the calibration tool can also serve as a verification tool by simply changing its orientation, i.e., by flipping, inverting, or causing it to rotate about the inversion axis. Thereby, after the initial calibration, no separate tool is required to verify the measurement system.

[0066] Preferably, the calibration tool has a longitudinal direction, wherein the calibration section and the verification section are arranged adjacent to each other in a transverse direction perpendicular to the longitudinal direction, and wherein the inversion axis extends between the calibration section and the verification section perpendicular to the longitudinal direction and the transverse direction.

[0067] In a further embodiment, the calibration tool includes one or more mounting elements for mounting the calibration tool relative to the measurement system to a support, wherein after inverting the calibration tool about the inversion axis, at least one of the one or more mounting elements is in the same position. Thus, the same one or more mounting elements can be used to mount the calibration tool in either position.

[0068] In another embodiment, the one or more calibration elements include a plurality of calibration elements arranged in a pattern extending in the longitudinal direction of the calibration tool, and wherein the one or more verification elements include a plurality of verification elements in different positions relative to the plurality of calibration elements in the longitudinal direction. By having the verification elements and the calibration elements in different positions, different values can be used to verify the measurement system to determine whether the ratio determined during calibration is correctly interpolated to the values expected by the verification elements.

[0069] In another embodiment, the measurement system includes a first camera and a second camera for respectively observing a first end and a second end of the calibration tool, and wherein the one or more verification elements include at least one verification element at the first end and at least one verification element at the second end. Thus, each camera can be calibrated by capturing images of the verification elements in the corresponding sections. Preferably, the one or more verification elements include a first set of two or more verification elements at the first end and a second set of two or more verification elements at the second end. More preferably, each set includes three or more verification elements.

[0070] In another embodiment, the one or more calibration elements and / or the one or more verification elements are through-holes. Thus, the calibration tool can be used in a backlight system, where a light bar is provided on one side of the calibration tool and a camera is provided on the opposite side of the calibration tool to capture the light passing through the through-holes.

[0071] In another embodiment, the one or more calibration elements include stepped features that enable the measurement system to also be calibrated in the height direction.

[0072] According to a ninth aspect, the present invention provides a method for verifying measurement values of a measurement system for measuring one or more tire components, wherein the measurement system includes at least one camera with a certain field of view, and wherein the method includes the following steps:

[0073] m) Providing a verification element with a predetermined size in the field of view of the at least one camera;

[0074] n) Measuring the one or more tire components and measuring the verification element simultaneously with or at a predetermined interval while measuring the one or more tire components;

[0075] o) Verifying the measured value of the verification element against the predetermined size of the verification element; and

[0076] p) Repeating steps n) and o) over time.

[0077] When verification is performed online, it can be repeated at any time during production, at specific intervals, or even continuously. Thus, when the measurement system is no longer properly calibrated due to wear or tolerances, immediate measures can be taken.

[0078] Where possible, the various aspects and features described and shown in this specification can be applied individually. These individual aspects, particularly those described in the appended independent claims, can be the subject of a divisional application. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The present invention will be elucidated based on exemplary embodiments shown in schematic drawings, in which:

[0080] Figure 1 A top view of a bead - apex drum with a bead - apex strip applied thereto and a measurement system for measuring the bead - apex strip is shown;

[0081] Figure 2 Shows along Figure 1 A cross - sectional view of the bead - apex drum and the bead - apex strip taken along line II - II in

[0082] Figure 3Shows a cross-sectional view of a bead - apex drum and a bead - apex taken along line III - III in Figure 1 ;

[0083] Figure 4 Shows a view of a calibration tool according to a first embodiment of the present invention, which is used to replace the bead - apex drum during a calibration method.

[0084] Figure 5 Shows a top view of the calibration tool according to Figure 4 ;

[0085] Figure 6 Shows a cross-sectional view of the calibration tool taken along line VI - VI in Figure 5 ;

[0086] Figure 7 Shows a cross-sectional view of the calibration tool taken along line VII - VII in Figure 5 ;

[0087] Figure 8 Shows a side view of a laser triangulation system according to a second embodiment of the present invention in an operating position;

[0088] Figure 9 Shows a side view of the measurement system according to Figure 8 in a calibration position;

[0089] Figure 10 Shows a top view of the measurement system in the calibration position of Figure 8 ;

[0090] Figure 11 Shows a view of a tire building drum with a clamping strip according to a third embodiment of the present invention;

[0091] Figure 12 Shows the clamping strip of Figure 11 alone;

[0092] Figure 13 Shows the details of the clamping strip according to the circle XIII in Figure 12 ;

[0093] Figure 14 Shows a view of a tire building drum with a first cover plate and a second cover plate according to a fourth embodiment of the present invention;

[0094] Figure 15 Shows the first cover plate of Figure 14 alone;

[0095] Figure 16 Shows the details of the first cover plate according to the circle XVI in Figure 15 ;

[0096] Figure 17 View showing a tyre forming drum and a verification tool according to a fifth embodiment of the present invention;

[0097] Figure 18 Shown separately is a front view of a calibration tool according to Figure 17 ;

[0098] Figure 19 Axonometric view showing a production line, a measuring system and a calibration tool for a strip or sheet according to a sixth embodiment of the present invention;

[0099] Figure 20 Shown separately is a top view of a calibration tool according to Figure 19 in a calibration position;

[0100] Figure 21 Shown is a top view of a calibration tool according to Figure 20 in a verification position;

[0101] Figure 22 Top view showing a calibration tool according to a seventh embodiment of the present invention; and

[0102] Figure 23 Shown is an axonometric view of a calibration tool according to Figure 22 ; DETAILED DESCRIPTION

[0103] Figure 1 、 2 and 3 show a bead - apex drum 7 for producing a bead - apex strip 8. In this exemplary embodiment, the bead - apex drum 7 is formed as a disc 70 having a central hub 71 and a bead - apex support surface 72 extending circumferentially around the central hub 71. The bead - apex drum 7 has a reference plane P, i.e., its mounting plane or its bottom surface, and a base profile B for supporting the bead - apex strip 8 relative to the reference plane P. The bead - apex drum 7 is typically mounted on a drum seat or a drum drive (not shown) and is driven to rotate about a rotation axis S1 which extends concentrically in a direction perpendicular to the reference plane P through the central hub 71.

[0104] The bead - apex strip 8 is formed by first applying a bead 80 on the bead - apex support surface 72 around the central hub 71 of the bead - apex drum 7 and then applying an apex strip 81 around the bead 80. The bead - apex support surface 72 may be slightly inclined to present a tapered orientation, i.e., at an angle inclined to the reference plane P. Different bead - apex drums may be provided for different bead - apex strips, depending on their respective dimensions, i.e., diameter, thickness and taper.

[0105] Figure 1 、 2 And 3 also shows a measuring system 9 for measuring the bead - apex 8 on the bead - apex drum 7. The measuring system 9 is preferably a laser triangulation system having a laser 90 for projecting a laser line L onto the bead - apex 8 and a camera 91 for capturing an image of the projected laser line L. The camera 91 has a field of view FOV as shown in Figure 2 shown.

[0106] Figure 4 -7 shows a calibration tool 1 for calibrating the measuring system 9 as shown in Figure 1 、 2 and 3. The calibration tool 1 is arranged to be placed in the same position as the bead - apex drum 7. In other words, when calibrating the measuring system 9, the calibration tool 1 temporarily replaces the bead - apex drum 7.

[0107] As shown in Figure 4 , the calibration tool 1 includes a tool body 10 which is rotatable about a rotation axis S1 perpendicular to a reference plane P relative to the measuring system 9. Preferably, the calibration tool 1 replaces the bead - apex drum such that the rotation axis S1 of the calibration tool 1 corresponds to the rotation axis S1 of the bead - apex drum 7 before its removal. Moreover, the tool body 10 may have similar mounting features, i.e., a mounting plane extending in the same plane as the mounting plane of the bead - apex drum before its removal. More particularly, the reference plane P for measuring the height on the bead - apex drum 7 and the calibration tool 1 may be the same. Thus, the calibration tool 1 can exhibit at least some of the characteristics of the bead - apex drum 7.

[0108] The rotation axis S1 extends axially and defines a radial direction R perpendicular to the rotation axis S1 and a circumferential direction C around the rotation axis S1.

[0109] In this exemplary embodiment, the tool body 10 extends only over a part of the entire perimeter around the rotation axis S1. In particular, the tool body 10 is formed as a circular segment. The tool body 10 can extend, for example, in a range of less than one hundred and eighty degrees of the perimeter around the rotation axis S1, preferably in a range of less than one hundred and twenty degrees. Alternatively, the tool body can extend over the entire perimeter, i.e., form a disc-shaped tool body similar to a disc-shaped bead - apex strip drum. The tool body can also be configured in an annular or ring shape as long as it can still be rotatably mounted around the rotation axis S1. The tool body 10 can have an integral or one-piece shape. Alternatively, the tool body 10 can include several interconnected parts, elements, segments or sections that form different features of the tool body 10, as described below.

[0110] As best seen in Figure 4 and 5 The tool body 10 is provided with a plurality of calibration surfaces 11 of a pattern G that defines a calibration position K. In this exemplary embodiment, each calibration surface 11 is different from the other calibration surfaces 11, i.e., is demarcated from the other calibration surfaces 11 by a distinct boundary. The calibration surfaces 11 can be formed, for example, by different interconnected parts of the tool body 10. Thus, each calibration surface 11 can be measured as a separate surface. Alternatively, the pattern G can be formed by a single continuous calibration surface (not shown), in which case the calibration position K is merely virtual or imaginary, i.e., the calibration position K is selected by the measurement system 9 according to a predetermined pattern. The continuous surface can hold an infinite number of calibration positions K, the number of which is limited only by the accuracy of the camera 91.

[0111] In Figure 5 the pattern G includes ten columns A1 - A10 extending radially R away from the rotation axis S1 and five rows B1 - B5 extending circumferentially C around the rotation axis S1. In this way, a radial grid of calibration positions K can be formed. When a greater or lesser number of calibration positions K is required, the number of columns A1 - A10 and rows B1 - B5 can be selected differently. To provide at least some useful amount of feedback to the measurement system 9, it seems that at least three columns and three rows are required.

[0112] As best visible in Figure 6 the radial cross-section of, for each column A1 - A10, the tool body is provided with recesses 12 extending between the respective calibration surfaces 11 within the corresponding column A1 - A10. Each recess 12 separates two calibration surfaces 11 in the radial direction R. At each transition from a respective calibration surface 11 to an adjacent recess in the recess 12, each calibration surface 11 within the corresponding column A1 - A10 defines a calibration edge 13. Conveniently, at least one calibration position K can be selected at one of the calibration edges 13.

[0113] As inFigure 6 best visible in a radial cross-section, for each of the columns A1 - A10, the height of the calibration position K within the respective column A1 - A10 relative to the reference plane P varies in a height direction H perpendicular to the reference plane P and / or parallel to the rotation axis S1. Similarly, as in Figure 7 best visible in a circumferential cross-section, for each of the rows B1 - B5, the height of the calibration position K within the respective row also varies in the height direction H relative to the reference plane P.

[0114] In this exemplary embodiment, for each of the columns A1 - A10, the calibration surfaces 11 within the respective column A1 - A10 extend in a common plane D, as Figure 6 shown. The common plane D extends at an inclined angle relative to the reference plane P. Alternatively, the respective calibration surfaces 11 may be in different planes, i.e., stepped and / or parallel planes (not shown). When stepped calibration surfaces 11 are used in the columns A1 - A10, the recesses 12 do not necessarily protrude between the respective calibration surfaces 11. For each of the columns A1 - A10, the inclination angle may be different or the same to reflect different shapes of the tread strips.

[0115] As Figure 7 shown, for each row, the respective calibration surfaces 11 within the respective row are stepped in the circumferential direction C in the height direction H from one calibration surface 11 to the next. Due to the steps between the respective calibration surfaces 11, recesses are not required. However, if the respective calibration surfaces 11 in the respective rows B1 - B5 are arranged similarly in a common plane (not shown) as the calibration surfaces 11 in the columns A1 - A10, recesses may also be provided between the respective calibration surfaces 11 in the respective rows B1 - B5.

[0116] From the above paragraphs, those skilled in the art will realize that the shape and relative orientation of the calibration surfaces 11 are allowed to vary, and the scope of the present invention need not be limited to any specific shape as long as the technical effect of providing a plurality of calibration positions K in the pattern G can be obtained. The transition from one calibration surface 11 to another may be, for example, stepped, abrupt, gradual, or smooth.

[0117] As Figure 6 best visible, for each of the columns A1 - A10, all of the calibration positions K within the respective column A1 - A10 have different heights in the height direction H relative to the reference plane P. More specifically, the height of the calibration position K within the respective column A1 - A10 relative to the reference plane P decreases successively or gradually in a radial direction R away from the rotation axis S1. Preferably, the successive decrease in height has a constant decrement or amount of decrease relative to the reference plane P.

[0118] As Figure 7Best visible in [reference document], for each row B1 - B5, all calibration positions K within the respective row B1 - B5 have different heights relative to the reference plane P in the height direction H. More specifically, the heights of the calibration positions K within the respective row B1 - B5 relative to the reference plane P increase successively or gradually in the circumferential direction C. Preferably, the successive increase in height has a constant increment relative to the reference plane P.

[0119] Thus, as Figure 4 shown in [reference document], the height of each calibration position K within the pattern G relative to the reference plane P in the height direction H is different from the height of the other calibration positions K within the same column A1 - A10 and the same row B1 - B5 relative to the reference plane P. In other words, each column A1 - A10 of calibration positions K forms a height profile with different heights at each calibration position K, while the height of each calibration position K within the respective column A1 - A10 is also different compared to the other calibration positions within the same row B1 - B5. Preferably, for each column A1 - A10, the decrement within each column A1 - A10 is the same, and / or, for each row B1 - B5, the increment within each row B1 - B5 is the same. In this case, the height profiles are shifted equally from one column A1 - A10 to the next.

[0120] Before calibration, the varying height of the calibration surface 11 relative to the reference plane P is predetermined, i.e., measured and verified, such that the measurement results of the measurement system 9 can be compared with the predetermined height of the calibration surface 11 to calibrate the measurement system 9.

[0121] The following will refer to Figure 1 -7 to illustrate a method for calibrating a measurement system 9, in particular a laser triangulation system, by using the aforementioned calibration tool 1.

[0122] The method comprises the following steps:

[0123] a) At least partially arrange the calibration tool 1 within the field of view FOV of the camera 91, as Figure 6 shown in [reference document];

[0124] b) Project a laser line L onto the calibration tool 1 with the laser triangulation system 9, as Figure 5 shown in [reference document];

[0125] c) Rotate the calibration tool 1 about the rotation axis S1 such that the laser line L is projected onto all calibration positions K within a respective one of the columns A1 - A10;

[0126] d) Capture an image of the laser line L projected onto all calibration positions K within the respective column A1 - A10 with the camera 91; and

[0127] e) Repeat steps c) and d) for another column within the columns A1 - A10.

[0128] In step a), the calibration tool 1 can be set such that its reference plane P is in the same position as the reference plane P of the bead - apex roller 7 during bead - apex production. Thus, there is no need to adjust the measurement system 9 to capture an image of the calibration tool 1.

[0129] By capturing an image of the laser line L in step d), calibration data regarding the height profiles of the respective columns A1 - A10 can be collected. In particular, any transitions, edges, or height variations can be captured and processed by a suitable processor in the measurement system 9. Preferably, step e) involves repeating steps c) and d) for all other columns A1 - A10. Thus, a maximum amount of calibration data can be collected.

[0130] For each of the columns A1 - A10, the calibration position K can be located on the calibration edge 13, as Figure 6 shown, such that the measurement system 9 can identify the transition at the calibration edge 13 as the calibration position K.

[0131] After capturing the images in step e), the measurement system 9 can be calibrated by associating the pixels in each captured image corresponding to the calibration position K of the respective columns A1 - A10 with a predetermined height of the calibration position K within the respective columns A1 - A10. In particular, the height of the calibration position K captured within the respective columns A1 - A10 can be used to determine the ratio of pixel - to - real - unit conversion, i.e., the ratio from pixels to micrometers, millimeters, or centimeters.

[0132] Optionally, the method may further include the following steps:

[0133] f) Before or after steps a) to e), provide an empty bead - apex roller 7 relative to the laser triangulation system 9, as Figure 1 shown in - 3, without the bead - apex 8;

[0134] g) Project the laser line L onto the empty bead - apex roller 7 with the laser triangulation system 9;

[0135] h) Capture an image of the laser line L projected onto the empty bead - apex roller 7; and

[0136] i) Determine the base profile B of the empty bead - apex roller 7 relative to the reference plane P of the empty bead - apex roller 7.

[0137] In step f), the bead - apex roller 7 is set such that its reference plane P is in the same position as the reference plane P of the calibration tool. Thus, there is no need to adjust the measuring system 9. Additionally, the height of the determined base profile B can be easily compared with the height of the calibration position K since they are measured relative to the same reference plane P.

[0138] Finally, the method may further include the following steps:

[0139] j) setting a bead - apex 8 on the bead - apex roller 7 as Figure 1 shown in - 3;

[0140] k) measuring the bead - apex 8 using the measuring system 9 as Figure 1 shown in - 3; and

[0141] l) subtracting the base profile B of the empty bead - apex roller 7 determined in step i) from the measured values.

[0142] The result after subtraction can represent the actual height of the bead - apex 8 relative to the bead - apex roller 7 in the height direction H.

[0143] Figure 8 and 9 FIG. shows an alternative laser triangulation system 109 according to a second embodiment of the present invention. The measuring system 109 includes a laser 190, a camera 191, and a guide roller, pulley, or drum 106 rotatable about a rotation axis S2 for guiding a strip 108 through the measuring system 109. The camera 191 has an optical axis M and a field of view FOV. The laser 190 is placed at an inclined angle relative to the optical axis M. The laser 190 is arranged to project a laser line L onto a calibration tool 101 in a lateral X1 parallel to the rotation axis S2 of the drum 106. The drum 106 has a circumferential surface 160 that supports the strip 108 at a zero level relative to the camera 191 of the measuring system 109. The laser 190 is arranged to project the laser line L onto the circumferential surface 160 of the drum 106 and through the strip 108 to measure the height profile of the strip 108 relative to the zero level. The measuring system 109 further includes a support member 192 for supporting the laser 190 and the camera 191 relative to the drum 106. The measuring system 109 is also provided with a calibration tool 101 for calibrating the measuring system 109.

[0144] As shown by comparing Figure 8 and Figure 9 shown, the support member 192 is pivotable about a pivot axis U between an operating position ( Figure 8 ) and a calibration position ( Figure 9) pivot between them. In the operating position, the camera 191 and the laser 190 are directed towards the drum 106 to measure the strip 108 on the drum. In the calibration position, the laser 190 and the camera 191 are directed towards the calibration tool 101. Preferably, the pivot axis U is parallel to the rotation axis S2. Preferably, the support 192 is arranged to pivot about the pivot axis U by at least forty-five degrees, and preferably at least sixty degrees, between the operating position and the calibration position.

[0145] Since the laser 190 and the camera 191 share the same support 192, they can pivot while maintaining the same relative orientation. In addition, the laser 190 and the camera 191 can pivot between the respective positions easily and quickly, i.e., during a short interruption in the production process of the strip 108 or even during the production process. Since the calibration position is different from the operating position, calibration can be performed offline.

[0146] As best visible in Figure 8 and 9 , the calibration tool 101 includes a tool body 110 that defines a reference plane Q. When the support 192 is in the Figure 9 calibration position, the reference plane Q is preferably perpendicular to the optical axis M of the camera 191.

[0147] As Figure 9 shown, the calibration tool 101 includes one or more first calibration surfaces 111 at a predetermined height relative to the reference plane Q in the height direction H2 perpendicular to the reference plane Q for calibrating the zero level. Preferably, the distance of the one or more first calibration surfaces 111 from the camera 191 in the calibration position is the same as the distance between the circumferential surface 160 and the camera 191 in the Figure 8 operating position.

[0148] As Figure 10 shown, the calibration tool 101 includes one or more second calibration surfaces 112, the height of which varies in the transverse direction X1 with respect to the reference plane Q in the height direction H2. In particular, the height of the one or more second calibration surfaces 112 varies in the transverse direction X1 according to a pattern that repeats at least twice, preferably at least three times, in the transverse direction X1. Thus, along a single laser line L, several heights corresponding to different second calibration surfaces 112 can be detected. The measurement data regarding the height of the second calibration surfaces 112 can be used to determine the scale of the measurement system 109, especially the scale for converting and / or correlating pixels in an image with actual units, i.e., microns, millimeters, or centimeters. By repeating the pattern, the camera can be calibrated with respect to more positions in the transverse direction X1, i.e., across most of the field of view FOV of the camera 191 in the transverse direction X1.

[0149] Figure 11 shows a tire building drum 206 and a bead 201 for clamping tire components to the drum 206. Generally, a measuring system (not shown) is arranged near the drum 206 to measure the shape, dimensions, and / or height of the tire components on the drum 206. The drum 206 has a rotational axis S3. The bead has a longitudinal direction Y1 and is arranged to be placed on the drum 206 in such a way that its longitudinal direction Y1 is parallel or substantially parallel to the rotational axis S3 of the drum 206. The bead is arranged to be held on the drum 206 by magnetic, vacuum, or mechanical holding means.

[0150] Such beads are known per se. However, as Figure 12 and 13 shown, the bead according to the invention is provided with a verification element 211 for verifying the measuring system. In particular, the bead 201 has a clamping side 202 and a non-clamping side 203, the clamping side 202 facing the tire component during clamping and the non-clamping side 203 being opposite to the clamping side 202. The verification element 211 is conveniently arranged on the non-clamping side 203 such that it is easily visible from the outside. More particularly, the verification element 211 is arranged at or near one end of the bead 201 in the longitudinal direction Y1 of the bead 201 such that it is less likely to be covered by the tire component during production.

[0151] In this exemplary embodiment, as Figure 13 shown in detail, the verification element 211 is a slot. However, those skilled in the art will recognize that many variants of the verification element 211 fall within the scope of the present invention as long as it can be used to verify the measured values, accuracy, calibration, and / or repeatability of the measuring system.

[0152] Figure 14 shows a tire building drum 306 that is rotatable about a rotational axis S4 extending in the axial direction W to receive one or more tire components (not shown). Generally, a measuring system (not shown) is arranged near the drum 306 to measure the shape, dimensions, and / or height of the tire components on the drum 306. The drum 306 includes a plurality of radially expandable and radially contractible segments. When the segments expand radially, the diameter and / or circumference of the drum 306 increases and an intermediate space is formed circumferentially between the segments. The drum 306 is provided with a plurality of cover plates 301, 302 for covering the intermediate space between the respective segments.

[0153] The plurality of cover plates 301, 302 includes one or more first cover plates 301, the first cover plate being provided with one or more verification elements 311 for verifying the measured values, accuracy, calibration and / or repeatability of the measurement system. The plurality of cover plates 301, 302 further includes one or more second cover plates 302, the second cover plate being provided with a plurality of calibration elements 312 for calibrating the measurement system. The calibration elements 312 are arranged in a regular pattern in the axial direction of the drum 306 on one or more second cover plates 302. The verification elements 311 of one or more first cover plates 301 are offset axially W with respect to the plurality of calibration elements 312 in one or more second cover plates 302.

[0154] Figure 15 and Figure 16 One of the first cover plates 311 is shown in more detail. The first cover plate 301 has a longitudinal direction Y2 and a first end 321, a second end 322 and a central portion 323 on the longitudinal direction Y2. In this exemplary embodiment, the measurement system includes a first camera, a second camera and a third camera arranged side by side for observing the first end 321, the second end 322 and the central portion 323 respectively. One or more verification elements 311 include a first group of two or more verification elements 311 at the first end 321, a second group of two or more verification elements 311 at the second end 322 and a third group of two or more verification elements 311 at the central portion 323. Preferably, each group includes three or more verification elements 311. More preferably, the three or more verification elements 311 in each group form the same pattern for each group.

[0155] Figure 17 A tire building drum 406 for receiving one or more tire components is shown. Generally, a measurement system (not shown) is arranged near the drum 406 to measure one or more of the tire components applied around the tire building drum 406. Figure 17 A verification tool 401 for verifying the measured values of the measurement system is also shown. The verification tool 401 includes: an annular body 410 that extends circumferentially around a central axis Z; and one or more reference elements 420 that exhibit the characteristics of the one or more tire components provided on the annular body 410. The annular body 410 is arranged to be concentrically assembled around or along the tire building drum 406. The verification tool 401 may generally correspond to the verification tool disclosed in WO 2016 / 122311 A1, which is incorporated herein by reference.

[0156] The position of the verification tool 401 on or along the tire building drum may have a slight error, especially in the axial direction W2 along or parallel to the central axis Z. This can be compensated as long as the center of the verification tool 401 is known. For this purpose, the verification tool 401 is provided with a center reference 411 for determining the center of the verification tool 401 in the axial direction W2.

[0157] Once the center is determined, the tire building drum 406 with the verification tool 401 around or beside it can move in the axial direction W2 until the verification tool 401 is in the position where the tire building drum 401 usually is during operation relative to the measuring system. Alternatively, the measuring system can slightly offset the measured values to compensate for any deviation of the center of the verification tool 401 relative to the measuring system.

[0158] Optionally, the verification tool 401 is provided with one or more end or side references 412 for determining one or more sides of the verification tool 401 in the axial direction W2. Preferably, the center reference 411 and the one or more side references 412 are arranged collinearly in the axial direction W2.

[0159] Figure 19 A strip production line 507 for producing a strip 508 is shown, especially for tire manufacturing. The strip production line 507 includes a conveyor 570, in this example a roller conveyor, which is interrupted along a measuring line T at a measuring position to allow a measuring system 509 to measure the characteristics of the strip 508 when the strip 508 passes through the interruption, namely the tread, carcass or ply (breaker), or the fold of the strip around the edge of the ply. In particular, the width of the strip 508 is measured at the measuring line T. In this example, the measuring system 509 includes a backlight unit 590 for emitting light towards the measuring line T and a first camera 591 and a second camera 592 opposite the backlight unit 590, so as to detect the light transmission along the side edges of the strip 508 at the measuring line T in a manner known per se.

[0160] To calibrate the measured values of the measuring system 509, a calibration tool 501 is provided. The calibration tool 501 is arranged to be installed between the backlight unit 590 and the cameras 591, 592 in the measuring position. As shown in Figure 20 more details, the calibration tool 501 includes a tool body 510 extending in the longitudinal direction Y3.

[0161] The tool body 510 includes a calibration section 502 with one or more calibration elements 521 and a verification section 503 with one or more verification elements 531. In Figure 20In [description], the calibration tool 501 is positioned at a calibration position in which the longitudinal Y of the tool body 510 extends parallel or substantially parallel to the measurement line T. In the calibration position, the measurement line T extends across one or more calibration elements 521 of the calibration section 502.

[0162] The calibration tool 501 is reversible or invertible about an inversion axis V1 between the calibration position as shown in Figure 20 and the verification position as shown in Figure 21 . In the verification position, the measurement line T extends across one or more verification elements 531 of the verification section 503. Thus, the calibration section 502 and the verification section 503 are effectively inverted. In other words, when inverted about the inversion axis V1, the positions of the calibration section 502 and the verification section 503 at the measurement line T are alternated or exchanged.

[0163] Preferably, the calibration section 502 and the verification section 503 are arranged adjacent to each other on a transverse X2 perpendicular to the longitudinal Y3. In this exemplary embodiment, the inversion axis V1 extends perpendicular to the longitudinal Y3 and the transverse X2 between the calibration section 502 and the verification section 503. More specifically, in this particular embodiment, the inversion axis V1 is upright, vertical or substantially vertical. Alternatively, the inversion axis may also extend parallel to the measurement line T between the calibration section 502 and the verification section 503, or pass through the centers of the two sections 502, 503 parallel to the transverse X2.

[0164] As shown in Figure 20 , the calibration tool 501 includes one or more mounting elements 505 for mounting the calibration tool 501 to a support relative to the Figure 19 measurement system 509. As shown by comparing Figure 20 and Figure 21 , preferably, at least one of the one or more mounting elements 505 is in the same position at least after inverting the calibration tool 501 about the inversion axis V1. Thus, the calibration tool 501 can be mounted in two positions in substantially the same manner.

[0165] As shown in Figure 20 and 21 , one or more calibration elements 521 include a plurality of calibration elements 521 arranged in a pattern extending on the longitudinal Y3 of the calibration tool 501. Similarly, one or more verification elements 531 include a plurality of verification elements 531. However, the verification elements 531 are offset from the calibration elements 521 in the longitudinal Y3.

[0166] As shown in Figure 19Best visible therein, the first camera 591 and the second camera 592 are respectively arranged for observing the first end 511 and the second end 512 of the calibration tool 501. In particular, the cameras 591, 592 observe the area where the side edges of the strip 508 in the calibration tool 501 generally cross the measurement line T. One or more verification elements 531 include a first set of two or more verification elements 531 at the first end 511 and a second set of two or more verification elements 531 at the second end 512. Preferably, each set includes three or more verification elements 531.

[0167] In this exemplary embodiment, one or more calibration elements 521 and / or one or more verification elements 531 are through-holes. This makes the calibration tool 501 suitable for use in a backlight measurement system. Alternatively, for example when calibrating and verifying a laser triangulation system, the calibration elements and verification elements can be provided as slits or protrusions.

[0168] Figure 22 and 23 An alternative calibration tool 601 according to a seventh embodiment of the present invention is shown, which differs from the calibration tool 501 according to the sixth embodiment of the present invention in that its calibration section 602 has one or more calibration elements 621 that are stepped or have stepped features 622 in the height direction H3 perpendicular to the longitudinal Y3 to allow for more precise calibration of the height measurement values of the camera. The verification section 603 similarly has verification elements 631 that are offset in the longitudinal Y3 with respect to the calibration elements 621. Similar to the calibration tool 501 according to the sixth embodiment of the present invention discussed previously, the alternative calibration tool 601 is reversible or invertible between a calibration position and a verification position about an inversion axis V2. In this case, the inversion axis V2 extends in the longitudinal Y3 between the calibration section 602 and the verification section 603.

[0169] In some of the above embodiments, the verification of the measurement values of the measurement system can be performed online, which means that the tire assembly can be measured while measuring one or more verification elements. In such an embodiment, the verification elements are arranged within the field of view of at least one camera of the measurement system. Then, the verification steps can be repeated over time, at regular intervals, or even continuously.

[0170] It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not intended to limit the scope of the present invention. From the above discussion, many variations will be obvious to those skilled in the art, and these variations are still covered by the scope of the present invention.

[0171] List of reference numerals

[0172] Calibration tool

[0173] 10 Tool body

[0174] 11 Calibration surface

[0175] 12 Recess

[0176] 13 Calibration edge

[0177] 7 Bead - filler roller

[0178] 70 Disc

[0179] 71 Central hub

[0180] 72 Bead - filler support surface

[0181] 8 Bead - filler

[0182] 80 Bead

[0183] 81 Filler

[0184] 9 Measuring system

[0185] 90 Laser

[0186] 91 Camera

[0187] 101 Calibration tool

[0188] 111 First calibration surface

[0189] 112 Second calibration surface

[0190] 106 Roller

[0191] 160 Circumferential surface

[0192] 108 Strip

[0193] 109 Measuring system

[0194] 190 Laser

[0195] 191 Camera

[0196] 192 Support

[0197] 201 Clip

[0198] 211 Verification element

[0199] 202 Clamping side

[0200] 203 Non - clamping side

[0201] 206 Roller

[0202] 301 First cover plate

[0203] 302 Second cover plate

[0204] 306 Tire forming drum

[0205] 311 Verification element

[0206] 312 Calibration element

[0207] 321 First end

[0208] 322 Second end

[0209] 323 Central part

[0210] 401 Verification tool

[0211] 406 Tire forming drum

[0212] 410 Tool body

[0213] 411 Central reference

[0214] 412 Side reference

[0215] 420 Reference element

[0216] 501 Calibration tool

[0217] 502 Calibration section

[0218] 521 Calibration element

[0219] 503 Verification section

[0220] 531 Verification element

[0221] 510 Tool body

[0222] 511 First end

[0223] 512 Second end

[0224] 505 Mounting element

[0225] 507 Strip production line

[0226] 570 Conveyor

[0227] 508 Strip

[0228] 509 Measuring system

[0229] 590 Backlight unit

[0230] 591 First camera

[0231] 592 Second camera

[0232] 601 Calibration tool

[0233] 602 Calibration section

[0234] 621 Calibration element

[0235] 622 Step

[0236] 603 Verification section

[0237] 631 Verification element

[0238] Columns A1 - A10

[0239] Rows B1 - B5

[0240] Circumferential C

[0241] Common plane D

[0242] Field of view FOV

[0243] Pattern or radial grid G

[0244] Height direction H1

[0245] Height direction H2

[0246] Height direction H3

[0247] Calibration position K

[0248] Laser line L

[0249] Optical axis M

[0250] Reference plane P

[0251] Reference plane Q

[0252] Radial R

[0253] Axis of rotation S1

[0254] Axis of rotation S2

[0255] Axis of rotation S3

[0256] Axis of rotation S4

[0257] Measurement line T

[0258] Axis of pivot U

[0259] Axis of inversion V1

[0260] Axis of inversion V2

[0261] Axial W1

[0262] Axial W2

[0263] X1 horizontal

[0264] X2 horizontal

[0265] Y1 vertical

[0266] Y2 vertical

[0267] Y3 vertical

[0268] Z central axis

Claims

1. A calibration tool for calibrating a laser triangulation system, wherein: The calibration tool comprises a tool body rotatable relative to the measuring system about a rotation axis perpendicular to a reference plane, wherein the tool body is provided with one or more calibration surfaces, the calibration surfaces defining a pattern of calibration positions, wherein the pattern comprises at least three columns extending radially away from the rotation axis and at least three rows extending circumferentially around the rotation axis, wherein, for each column, the height of the calibration positions within the corresponding column varies relative to the reference plane in a height direction perpendicular to the reference plane, and wherein, for each row, the height of the calibration positions within the corresponding row varies relative to the reference plane in the height direction.

2. The calibration tool according to claim 1, characterized in that The pattern forms a radial grid of calibration positions.

3. The calibration tool according to claim 1, characterized in that For each column, at least half of the calibration positions in the corresponding column have different heights in the height direction relative to the reference plane.

4. The calibration tool according to claim 1, characterized in that For each column, the height of the calibration positions within the corresponding column relative to the reference plane decreases successively in radial direction away from the rotation axis.

5. The calibration tool according to claim 4, characterized in that The successive reductions in height have a constant decrement relative to the reference plane.

6. The calibration tool according to claim 4, characterized in that The sequential reduction in height follows a certain curvature to match or correct for a specific lens distortion effect.

7. The calibration tool according to claim 1, characterized in that For each row, at least half of the calibration positions within the corresponding row have different heights in the height direction relative to the reference plane.

8. The calibration tool according to claim 1, characterized in that For each row, the heights of the calibration positions in the corresponding row relative to the reference plane increase sequentially in the circumferential direction.

9. The calibration tool according to claim 8, characterized in that The successive increases in height have a constant increment relative to the reference plane.

10. The calibration tool according to claim 1, characterized in that Each calibration position within the pattern has a height relative to the reference plane in the height direction that is different from the height relative to the reference plane of other calibration positions in the same column and row.

11. The calibration tool according to claim 1, characterized in that For each column, the one or more calibration surfaces include a separate calibration surface for each calibration position within the corresponding column.

12. The calibration tool according to claim 11, characterized in that For each row, the tool body is provided with recesses extending between the calibration surfaces in the respective row to radially separate the calibration surfaces.

13. The calibration tool according to claim 12, characterized in that Each calibration surface within a respective column defines a calibration edge at each transition from the respective calibration surface to an adjacent one of the recesses, wherein at least one calibration position is located at one of the calibration edges.

14. The calibration tool according to claim 11, characterized in that For each column, the calibration surfaces within the respective column extend in a common plane, wherein the common plane extends at an oblique angle relative to the reference plane.

15. The calibration tool according to claim 1, characterized in that For each row, the one or more calibration surfaces include a separate calibration surface for each calibration position within the corresponding row.

16. The calibration tool according to claim 15, characterized in that For each row, the calibration surfaces within the respective row are stepped in the height direction along the circumferential direction from one calibration surface to the next calibration surface.

17. The calibration tool according to claim 1, characterized in that The pattern comprises at least five columns.

18. The calibration tool according to claim 1, characterized in that The pattern comprises at least four rows.

19. The calibration tool according to claim 1, characterized in that The tool body extends over only a portion of the entire circumference about the rotation axis.

20. The calibration tool according to claim 19, characterized in that The tool body is formed as a circular segment.

21. A method of calibrating a laser triangulation system using the calibration tool according to claim 1, wherein: The laser triangulation system comprises a laser and a camera with a field of view, wherein the method comprises the following steps: a) providing said calibration tool at least partially within said field of view of said camera; b) projecting a laser line onto the calibration tool using the laser triangulation system; c) rotating the calibration tool about a rotation axis so that the laser line is projected onto all calibration positions of a respective one of the columns; and d) capturing with said camera an image of the laser line projected on all calibration positions of the corresponding said column.

22. The method according to claim 21, characterized in that The method further comprises the following steps: e) Repeat steps c) and d) for the other column.

23. The method according to claim 22, characterized in that The step e) comprises the following steps: repeating the steps c) and d) for all other columns.

24. The method according to claim 22, characterized in that The height of the calibration position of each column relative to the reference plane is predetermined, wherein the method further comprises the step of calibrating the laser triangulation system by associating a pixel in each captured image corresponding to a calibration position in the corresponding column with the calibration position within the corresponding column.

25. The method according to claim 21, characterized in that The method further comprises the following steps: f) before or after steps a) to d), providing an empty bead-apex cylinder relative to the laser triangulation system, wherein the bead-apex cylinder has a reference plane and a base profile for supporting the bead-apex relative to the reference plane, wherein the empty bead-apex cylinder is arranged with its reference plane at the same position as the reference plane of the calibration tool; g) projecting a laser line onto the empty bead-apex roller using the laser triangulation system; h) capturing an image of a laser line projected onto said empty bead-apex drum; and i) Determining a base profile of the empty bead-apex cylinder relative to a reference plane of the empty bead-apex cylinder.

26. The method according to claim 25, characterized in that The method further comprises the following steps: j) providing a bead-apex strip on said bead-apex strip drum; k) measuring the bead-apex using the measuring system; and l) Subtracting the basic profile of the empty bead-apex cylinder determined in step i) from the measured values.

Images