Systems and methods for visually aligning terahertz radiation beams

Abstract

A system for measuring the coating thickness on a target surface includes a terahertz spectroscopy device and a reference image projector. The terahertz spectroscopy device includes a radiation head operable to project a terahertz radiation beam onto the target surface and receive the reflected beam. The reference image projector includes a visible light device and is operable to project a reference image onto the target surface using the visible light device. Visual characteristics of the reference image indicate at least one of a distance, a rotational alignment, and an angular alignment of the radiation head relative to the target surface.

Description

Technical Field

[0001] The present invention relates to systems and methods for aligning a terahertz radiation beam to measure the thickness of multiple layers on a surface. Background Art

[0002] The descriptions in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] The exterior of a vehicle generally includes multiple paint layers and / or other coatings, such as an electrocoat, a primer, a basecoat, and a clearcoat. Each layer has a minimum film formation, which is designed to inhibit deterioration and potential delamination of the exterior caused by, for example, UV and visible light, and provides an appropriate appearance / color for the vehicle and protects the substrate from environmental damage.

[0004] Although various paint thickness measurement techniques can be used to measure a single paint layer, there are a limited number of non-destructive measurement techniques for measuring multiple layers. One such measurement technique utilizes ultrasonic technology, where an ultrasonic transducer is placed on the outer surface and an ultrasonic signal is sent through the outer surface. A liquid couplant (usually water) is used to transmit the signal into the coating material. The ultrasonic signal generates echoes at the layer interfaces, and the thickness is determined based on the time difference between consecutive echoes. The sound velocity values vary between different coatings, so calibration is performed on all layers in addition to the various basecoat colors.

[0005] Although ultrasonic technology is effective, there are some problems with this technology. For example, the transducer size and the tool for the transducer may not allow measurement of certain vehicle surfaces, such as windshield flanges, and thus, a separate process is typically employed to obtain data for those areas. Another problem is that the transducer requires a large (e.g., 10 mm diameter) flat area in order to generate a sufficient waveform. This requires selection of these points based on the flatness of the points on the vehicle, rather than being able to select positions of interest on the vehicle that may not be flat. In addition, the transducer physically contacts the vehicle. Although the transducer may not be damaged, the water left on the vehicle affects other quality control measures, such as dirt detection quality inspections.

[0006] Another technique for measuring multi-layer surfaces involves using a radiation beam with a terahertz (THz) frequency. In the case of generating a THz radiation beam using a THz light source, the THz head is positioned at a specified offset and perpendicular to the target surface of the vehicle before performing the measurement. For example, the radiation head can be attached to a robot or some other automated piece to allow it to track contoured surfaces and complex geometries. The THz radiation beam is emitted from the THz radiation head and reflected from the vehicle due to a change in the refractive index. The time difference between the emission and the reflection is used to calculate the thickness. Due to the change in the refractive index, the THz signal is reflected from the coating interface, and the time difference of the reflection is used to calculate the thickness.

[0007] Since the THz head is relatively compact and does not contact the vehicle surface, it can be used to measure locations that cannot be measured by ultrasonic transducers, such as the windshield flange. The diameter of the THz radiation beam is typically 1 mm, which enables the measurement of multiple areas of flat sections of that size.

[0008] However, for optimal measurement, the THz radiation head should be aligned perpendicular to the target surface of the vehicle so that the emitter of the radiation head is aligned with the detector of the radiation head. When the emitter and the detector are aligned, the amplitude of the reflected radiation signal is typically at its maximum. If the radiation head is not perpendicular to the surface, the reflected radiation signal may not be aligned with the detector, which results in a lower peak amplitude. This loss of signal can affect the result of the thickness measurement. Misalignment during the calibration process can also produce an incorrect calibration file and bad data. These and other problems are solved by the teachings of the present disclosure. Summary of the Invention

[0009] This section provides a general overview of the present disclosure and is not a full disclosure of the entire scope of the present disclosure or all of its features.

[0010] In one form, the present disclosure relates to a system for measuring the thickness of a coating on a target surface. The system includes a terahertz spectroscopy device and a reference image projector. The terahertz spectroscopy device includes a radiation head that is operable to project a terahertz radiation beam onto the target surface and receive the reflected beam. The reference image projector includes a visible light device and is operable to project a reference image onto the target surface using a visible light source. The visual characteristics of the reference image indicate at least one of the distance, rotational alignment, and angular alignment of the radiation head relative to the target surface.

[0011] In another form, the terahertz spectroscopy device includes: a terahertz light source that is operable to generate the terahertz radiation beam; and a radiation head that includes an emitter that emits the terahertz radiation beam and a detector for receiving the reflected beam.

[0012] In yet another form, the visible light device is positioned together with the radiation head.

[0013] In one form, the system further includes a controller configured to control the position and orientation of the radiation head relative to the target surface based on the visual characteristics of the reference image.

[0014] In another form, the reference image includes at least two patterns superimposed on each other. Each pattern has visual characteristics according to the position of the radiation head relative to the target surface and is independent of other patterns.

[0015] In yet another form, one of the at least two patterns is a plurality of points arranged in a matrix form, and the other of the at least two patterns is a plurality of rings having different diameters and positioned concentrically with each other.

[0016] In one form, the at least two patterns are different geometric shapes superimposed on each other.

[0017] In another form, the visual characteristics of the reference image include at least one of size, distortion, and rotational position.

[0018] In one form, the present disclosure relates to a method for aligning a terahertz radiation head of a spectroscopic device with a target surface. The method includes: projecting a reference image onto the target surface by a visible light source; analyzing the visual characteristics of the reference image to determine the alignment of the terahertz radiation head relative to the target surface; and aligning the terahertz radiation head with the target surface such that the visual characteristics of the reference image are within the calibrated visual characteristics. The terahertz radiation beam emitted from the terahertz radiation head is surrounded by the reference image, and the visual characteristics of the reference image indicate at least one of the distance, angle, and rotational orientation of the terahertz radiation head.

[0019] In another form, the calibrated visual characteristics represent the reference image when the alignment of the terahertz radiation head relative to the target surface is optimal for receiving a reflected terahertz radiation beam from the target surface.

[0020] In yet another form, projecting the reference image further includes projecting at least two patterns superimposed on each other onto the target surface to form the reference image.

[0021] In one form, the present disclosure relates to a method for aligning a terahertz radiation head of a spectroscopic device with a target surface of a vehicle. The method includes: projecting an image onto the target surface using a visible light source; and aligning the terahertz radiation head with the target surface until visual characteristics of the image satisfy calibrated characteristics. The calibrated characteristics represent the image when the terahertz radiation head is in a calibrated position.

[0022] In another form, projecting the image further includes projecting two patterns superimposed on each other onto the target surface to form a reference image. Each pattern has visual characteristics according to the position of the terahertz radiation head relative to the target surface and is independent of the other pattern.

[0023] In yet another form, the visual characteristics of the image indicate at least one of a distance, an angle, and a rotational orientation of the terahertz radiation head.

[0024] Additional application areas will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for illustrative purposes only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] For a better understanding of the present disclosure, various forms thereof will now be described by way of example with reference to the accompanying drawings, in which:

[0026] Figure 1 is a schematic diagram of a terahertz (THz) sensing system with a reference image projector according to the teachings of the present disclosure;

[0027] Figure 2 is Figure 1 a schematic diagram of the radiation head of the system of

[0028] Figure 3A shows an optical device of a reference image projector arranged together with the radiation head according to the teachings of the present disclosure;

[0029] Figure 3B and Figure 3C shows a pattern formed by the Figure 3A optical device of

[0030] Figure 3D shows a reference image formed by the Figure 3B and Figure 3C patterns of

[0031] Figure 4A and Figure 4B show the rotational relationship between the radiation head and the light pattern according to the teachings of the present disclosure;

[0032] Figure 5A 、 Figure 5Band Figure 5C shows different visual characteristics of a reference image based on the position of a radiation head in accordance with the teachings of the present disclosure; and

[0033] Figure 6 is a flowchart of a radiation head alignment routine in accordance with the teachings of the present disclosure.

[0034] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Detailed Description

[0035] The following description is merely exemplary in nature and is in no way intended to limit the present disclosure, its application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0036] Terahertz radiation beams are invisible to the human eye and thus it may be difficult to align a radiation head such that it is perpendicular to a target surface. While some systems include a single visible laser beam aligned with the radiation head to assist in the alignment of the radiation head, the laser beam does not provide an indication to the operator of the distance from the radiation head nor an indication of the rotation of the radiation head.

[0037] The present disclosure relates to a terahertz sensing system that includes a reference image projector for projecting a reference image onto a target surface of a vehicle, the reference image projector providing a visual tool for aligning a radiation head of the system with the target surface. As also described herein, visual characteristics of the reference image are used to indicate, for example, the distance and rotational alignment of the radiation head relative to the target surface.

[0038] Reference Figure 1 , a terahertz (THz) sensing system 100 is used to measure the thickness of one or more paint layers on a vehicle body 102. The system 100 includes a light source 106, a radiation head 108 coupled to the light source 106, and a controller 110. The light source 106 is operable to generate a radiation beam 112 in the THz frequency range. Thus, the radiation beam 112 is in the electromagnetic spectrum region that includes microwave and infrared light waves. The radiation beam 112 can penetrate a variety of materials and travel in a line of sight.

[0039] In one form, the radiation head 108 is coupled to the light source 106 by an optical fiber cable and is arranged and attached to a movable member 114, such as a robotic arm. The movable member 114 is operable to adjust the orientation and position of the radiation head 108. Reference Figure 2, the radiation head 108 includes a transmitter 202 and a detector 204. The transmitter 202 emits or radiates a radiation beam 112 generated by the light source 106 along the vehicle body 102 towards the target surface 208. The detector 204 receives one or more reflected radiation beams 210 reflected from the vehicle body 102. The radiation head 108 is communicatively coupled to the controller 110, such as by wiring, and transmits data indicative of the reflected radiation beam 210 to the controller 110.

[0040] The controller 110 is a computer including, for example, a processor, a computer-readable medium, and other electronic components. The controller 110 is also connected to one or more user interfaces 115, such as a keyboard and a monitor (e.g., a liquid crystal display), to allow an operator to view one or more graphical user interfaces configured for operating the system 100. The controller 110 is configured to control the light source 106 and the radiation head 108 to emit a THz radiation beam 112. The controller 110 also analyzes the signal received from the radiation head 108 to determine the thickness of one or more paint layers of the target surface 208. An example of such an analysis is provided in the co-pending U.S. application Ser. No. 14 / 829,888, filed on Aug. 19, 2015, and titled "ROBOTIC VEHICLE PAINTING INSTRUMENT INCLUDING A TERAHERTZ RADIATION DEVICE", which is commonly owned with this application and the content of which is incorporated herein by reference in its entirety.

[0041] To align the radiation head 108 with the target surface 208, the system 100 also includes a reference image projector 116 ( Figure 1 ), and the reference image projector 116 projects a reference image onto the target surface 208 using one or more visible light devices. The reference Figures 3A to 3D , in one form, the reference image projector 116 includes two visible light devices 302A and 302B (i.e., collectively the light devices 302) for generating the reference image. The light devices 302 are provided together with the radiation head 108 and can be any suitable visible light device, such as a visible laser device.

[0042] The light device 302 is configured to project different images to form a reference image. In one form, the light device 302A forms a linear pattern 304 that includes a plurality of points arranged along two orthogonal axes, and the light device 302B forms a circular pattern 306 that has a plurality of rings with different diameters and is concentrically arranged with each other. In another form, the circular pattern 306 can be offset to a shallow angle such that a slight change in the angle causes a large deformation of the projected pattern for visual evaluation as further described below. The light device 302 is configured to project the corresponding images such that the images are superimposed to form a reference image 308. The light device 302 can be configured to form other suitable geometries and / or patterns, and thus the patterns and the reference image are not limited to the points and rings shown herein.

[0043] When the reference image projector 116 is arranged together with the radiation head 108, the position and rotation of the radiation head 108 affect one or more visual characteristics of the pattern projected by the light device 302. For example, Figure 4A shows the rotational relationship of the radiation head 108 and the linear pattern 304 about the z-axis, and Figure 4B shows the rotational relationship of the radiation head 108 and the circular pattern 306 about the X-Y axis. As shown, the visual characteristics of the patterns 304 and 306 are based on the position of the radiation head 108, and thus can be related to one or more position characteristics of the radiation head 108 relative to the target surface 208.

[0044] The reference image projector 116 is arranged together with the radiation head 108 such that the radiation beam 112 is surrounded by the reference image 308, and when the radiation head 108 is in a measurement position relative to the target surface 208 (e.g., the radiation head 108 is perpendicular to the target surface 208 and at a specified offset from the target surface 208), the visual characteristics of the reference image 308 are within one or more calibrated visual characteristics. The visual characteristics include but are not limited to at least one of the size, deformation, and rotational position of the reference image 308. For example, Figure 3D shows the reference image 308 having calibrated visual characteristics when the radiation head 108 is in the measurement position. At the measurement position, the circular pattern 306 is positioned within the boundary formed by the linear pattern 304, the linear pattern 304 forms a square grid composed of a plurality of points, and the circles of the circular pattern 306 are concentrically arranged with each other.

[0045] The visual characteristics of the reference image 308 indicate the positional relationship of the radiation head 108 relative to the target surface 208. Such positional relationship includes but is not limited to the distance, rotational alignment, and angular alignment of the radiation head 108 relative to the target surface 208. For example, Figures 5A to 5C shows the reference image when the radiation head 108 is in a position other than the measurement position relative to the target surface 208. In Figure 5Ain which the circular pattern 306 is larger than Figure 3D the circular pattern, and is related to a position too far from the target surface 208 relative to the distance of the radiation head 108. Conversely, in Figure 5B the circular pattern 306 is smaller than Figure 3D the circular pattern, and is related to a position too close to the target surface 208 relative to the distance of the radiation head 108. In Figure 5C the linear pattern 304 rotates and the circular pattern 306 is deformed, which is related to a position where the radiation head 108 is too close to the target surface 208 and not perpendicular to the target surface 208. Other correlations between the visual characteristics of the reference image and various positions of the radiation head 108 are possible and are within the scope of the present disclosure.

[0046] In the case of using the calibrated visual characteristics and the predetermined correlation between the visual characteristics of the reference image and the position of the radiation head 108, a visual evaluation of the reference image projected on the target surface 208 is performed to align the radiation head 108 with the target surface 208. In one form, the visual evaluation is performed by an operator who adjusts the position of the radiation head 108 by operating the movable member 114 until the reference image projected on the target surface 208 is within the calibrated visual characteristics.

[0047] In another form, the system 100 is configured to include a visual recognition instrument that compares the visual characteristics of the reference image with the calibrated visual characteristics and uses the pre-stored correlation between the visual characteristics and the position of the radiation head 108 to align the radiation head 108. For example, the visual recognition instrument has a camera that captures an image of the reference image and transmits the captured image to the controller 110. The controller 110 is configured to determine the position of the radiation head 108 based on the captured image of the reference image and align the radiation head 108 by controlling the movable member 114 until the visual characteristics of the reference image substantially match the visual characteristics of the calibrated visual characteristics. In yet another form, the visual evaluation is performed by a combination of the operator and the controller 110. For example, when the visual characteristics of the reference image are significantly different from the calibrated visual characteristics, the operator can make an initial adjustment to the radiation head 108 and then operate the controller 110 to perform further analysis to further adjust the position of the radiation head.

[0048] In one form, the controller 110 can display an animated representation of the movable member 114, the radiation head 108, and the target surface 208 on a monitor. In the animated representation, the controller 110 displays one or more markers for indicating the position of the radiation head 108 relative to the target surface 208 based on a visual evaluation of a reference image. For example, the controller 110 can show circular bubbles displayed in different colors and / or sizes for indicating the distance between the radiation head 108 and the target surface. Other markers can be used to indicate angular measurements. Such visual indicators assist the operator in aligning the radiation head 108 with the target surface.

[0049] Reference Figure 6 , a radiation head alignment routine 600 executed by the system 100 is provided. At 602, the system 100 projects a reference image onto the target surface and analyzes one or more visual characteristics of the reference image. For example, the controller 110 operates the reference image projector 116 to project the reference image onto the target surface. The visual characteristics of the reference image can be analyzed by the controller 110, an operator of the system 100, or a combination thereof.

[0050] At 604, a visual evaluation is performed to determine whether one or more visual characteristics of the reference image are within corresponding calibrated visual characteristics. For example, the size, rotation, and / or distortion of the projected reference image are compared with the calibrated size, calibrated rotation, and / or calibrated distortion.

[0051] If one or more visual characteristics are not within the corresponding calibrated visual characteristics, then at 606, the position of the radiation head 108 is adjusted based on the analysis of the visual characteristics and predetermined correlation information. For example, in one form, the size of the reference image is related to the distance of the radiation head 108 relative to the target surface 208. Thus, if the size of the reference image is smaller than the calibrated size, then the radiation head 108 is too close to the target surface. From 606, the visual characteristics of the reference are compared with the calibrated visual characteristics again at 604. If the visual characteristics are within the calibrated visual characteristics, then at 608, it is determined that the radiation head 108 is correctly aligned with the target surface 208 to perform paint thickness evaluation, and the alignment routine 600 ends.

[0052] By using the reference image projector, an invisible terahertz radiation beam can be visualized to accurately align the radiation head relative to the target surface by the operator and / or the controller. In the example provided herein, the reference image includes two patterns superimposed on each other. By superimposing the two patterns on each other, the rotation and distance about three axes of the terahertz radiation head can be determined.

[0053] The description of the present disclosure is merely exemplary in nature, and thus, variations that do not depart from the essence of the present disclosure are intended to fall within the scope of the present disclosure. These variations should not be regarded as departing from the spirit and scope of the present disclosure.

[0054] According to the present invention, a method for aligning a terahertz radiation head of a spectroscopic device with a target surface of a vehicle, the method being provided as having: projecting an image onto the target surface using a visible light source; and aligning the terahertz radiation head with the target surface until visual characteristics of the image satisfy calibrated characteristics, wherein the calibrated characteristics represent the image when the terahertz radiation head is in a calibrated position.

[0055] According to an embodiment, projecting the image further includes projecting two patterns superposed on each other onto the target surface to form a reference image, wherein each pattern has visual characteristics according to a position of the terahertz radiation head relative to the target surface and is independent of the other pattern.

[0056] According to an embodiment, one of the two patterns is a plurality of points arranged in a matrix form, and the other of the two patterns is a plurality of rings having different diameters and positioned concentrically with each other.

[0057] According to an embodiment, the two patterns are different geometric shapes superposed on each other.

[0058] According to an embodiment, the visual characteristics of the image include at least one of a size, a deformation, and a rotational position of the image.

[0059] According to an embodiment, the visual characteristics of the image indicate at least one of a distance, an angle, and a rotational orientation of the terahertz radiation head.

Claims

1. A system for measuring the thickness of a coating on a target surface, the system comprising: A terahertz spectroscopy device, the terahertz spectroscopy device including a radiation head operable to project a terahertz radiation beam onto the target surface and receive the reflected beam; And A reference image projector, the reference image projector including a visible light device and operable to project a reference image onto the target surface using the visible light device, wherein the visual characteristics of the reference image indicate at least one of the distance, rotational alignment, and angular alignment of the radiation head relative to the target surface; Wherein projecting the reference image further comprises projecting at least two patterns superimposed on each other onto the target surface to form the reference image.

2. The system according to claim 1, wherein: The terahertz spectroscopy device includes a terahertz light source operable to generate the terahertz radiation beam, and The radiation head includes a transmitter for emitting the terahertz radiation beam and a detector for receiving the reflected beam.

3. The system according to claim 1, wherein the visible light device is positioned together with the radiation head.

4. The system according to claim 1, the system further comprising a controller configured to control the position and orientation of the radiation head relative to the target surface based on the visual characteristics of the reference image.

5. The system according to claim 4, wherein the reference image includes at least two patterns superimposed on each other, each pattern having visual characteristics according to the position of the radiation head relative to the target surface and independent of other patterns.

6. The system according to claim 5, wherein one of the at least two patterns is a plurality of points arranged in a matrix form, and the other of the at least two patterns is a plurality of rings having different diameters and positioned concentrically with each other.

7. The system according to claim 5, wherein the at least two patterns are different geometric shapes superimposed on each other.

8. The system according to any one of claims 1 to 4, wherein the visual characteristics of the reference image include at least one of size, distortion, and rotational position.

9. A method for aligning a terahertz radiation head of a spectroscopy device with a target surface, the method comprising: Projecting a reference image onto the target surface through a visible light source, wherein the terahertz radiation beam emitted from the terahertz radiation head is surrounded by the reference image; Analyzing the visual characteristics of the reference image to determine the alignment of the terahertz radiation head relative to the target surface, wherein the visual characteristics of the reference image indicate at least one of the distance, angle, and rotational orientation of the terahertz radiation head; And Aligning the terahertz radiation head with the target surface such that the visual characteristics of the reference image are within calibrated visual characteristics; Wherein projecting the reference image further comprises projecting at least two patterns superimposed on each other onto the target surface to form the reference image.

10. The method according to claim 9, wherein the calibrated visual characteristic represents the reference image when the alignment of the terahertz radiation head relative to the target surface is optimal for receiving the reflected terahertz radiation beam from the target surface.

11. The method according to claim 9, wherein one of the at least two patterns is a plurality of points arranged in a matrix form, and the other of the at least two patterns is a plurality of rings having different diameters and positioned concentrically with each other.

12. The method according to claim 9, wherein the at least two patterns are different geometric shapes superimposed on each other.

13. The method according to claim 9 or 10, wherein the visual characteristic of the reference image includes at least one of size, distortion, and rotational position.

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