JP2024069627A - Imaging system for surface inspection - Google Patents

Abstract

To provide an imaging system and a method for evaluating heterogeneity or non-uniformity in a reflective display such as assembled display modules of a type found in smartphones, tablets and the like.SOLUTION: A system includes incoherent light such as a light-emitting diode (LED) which is polarized and collimated. A surface to be evaluated is perpendicular to the collimated light, thereby the light hits directly on the surface. Polarization of the light is altered before and after reflection, and the reflected light from the surface to be evaluated is received by a sensor. Heterogeneity or non-uniformity of the surface will appear in a sensed image as contrast variation. Because reflection from the surface to be evaluated is 180 degrees reflection, the sensed image can be in sharp focus across the entire surface to be evaluated. Optionally, the system may utilize a single collimation lens without a collection lens for efficiency and compactness.SELECTED DRAWING: Figure 1

Description

This application claims the benefit under 35 U.S.C. § 199 of U.S. Provisional Patent Application No. 62/883,924, entitled "IMAGING SYSTEM FOR SURFACE INSPECTION," filed August 7, 2019, the entire disclosure of which is expressly incorporated herein by reference.

This application relates to testing and detecting surface unevenness in flat reflective optical elements and displays. More particularly, it relates to assessing the planarity or evenness of displays and assembled display modules.

The waviness, or lack of planarity, of flat panel displays is an important parameter for providing insight into lamination process control and for providing an indication of the quality of the final product. It is becoming increasingly important that display modules have a uniformly high degree of planarity (i.e., flatness). Non-uniformities in planarity (e.g., waviness) may be visible to end users of the display module, especially when viewed at certain angles. The waviness or other non-uniformities result in a poor user experience.

Improvements to the above are needed.

The present disclosure is directed to an imaging system and method for evaluating the non-uniformity or unevenness of a reflective display, such as an assembled display module of the type found on smartphones, tablets, and the like. The system includes incoherent light, such as a polarized light emitting diode (LED). The surface to be evaluated is perpendicular to the incident light, so that the light impinges directly on the surface. The polarization of the light is changed before and after reflection, and the reflected light from the surface under evaluation is received by a sensor to form an image. Non-uniformity or unevenness of the surface appears as contrast changes in the sensed image. Because the reflection from the surface under evaluation is a 180° reflection, the sensed image can be sharply focused across the entire surface to be evaluated. Optionally, the system may utilize a single collimation lens without a collection lens for efficiency and compactness.

In a first system and method, incoherent light passes through a polarizing beam splitter and shines directly (i.e. perpendicularly) on the surface to be evaluated. The surface to be evaluated may be an assembled display module. The light reflected from the display module switches polarization by 90° and is then reflected 90° by the polarizing beam splitter. The light then passes through a knife edge or aperture in its path to a camera or imaging sensor. The camera or imaging sensor images the display module via the reflected light. Any unevenness in the non-uniform surface creates contrast variations in the image of the display module, which facilitates visualization of any unevenness in the surface to be evaluated.

In a second system and method, the incoherent light passes through a first linear polarizer, then through a non-polarizing beam splitter, and shines directly (i.e., perpendicularly) on the surface to be evaluated. The surface to be evaluated may be an assembled display module. The light reflected from the display module switches polarization by 90° and is then reflected by the non-polarizing beam splitter. The light then passes through a second polarizer and a knife edge or aperture in its path to a camera or imaging sensor. The camera or imaging sensor images the display module via the reflected light. Any unevenness in the non-uniform surface creates contrast variations in the image of the display module, which facilitates visualization of any unevenness in the surface to be evaluated.

In a third method, a similar arrangement to the second method is used with the addition of a cylindrical lens after the collimation lens, thereby generating a 1D focused wavefront. If the radius of the wavefront is identical to the radius of the curved surface to be evaluated, this shape can generate the same Schlieren-type images used in the first and second methods and devices, because the reflected light of the surface to be evaluated will follow the same optical path after passing through the cylindrical lens both before and after reflection as the reflection from the flat display described above.

In one embodiment, the present disclosure provides an imaging system including an incoherent light source that emits an incoherent optical signal, a collimation lens positioned to receive one of the incoherent optical signal and the first optical signal and that emits a collimated optical signal, and a polarizer operatively disposed between the incoherent light source and a sensor. The sensor has a sensor lens that defines a sensor lens plane positioned substantially perpendicular to the incoherent optical signal emitted from the light source. The sensor is positioned to receive a reflection of the collimated optical signal.

In another embodiment, the present disclosure provides a method for evaluating imperfections in a surface to be evaluated. The method includes emitting an incoherent optical signal, passing the incoherent optical signal through a beam splitter to produce a first optical signal and a second optical signal, where the first optical signal is at an angle relative to the second optical signal, passing at least a portion of the incoherent optical signal through a collimation lens to produce a collimated optical signal, reflecting the collimated optical signal on the surface to be evaluated to produce a reflected optical signal, where the surface to be evaluated defines a plane of the evaluation surface that is substantially perpendicular to the collimated optical signal, and sensing the reflected optical signal at a sensor to produce a sensed image.

The above and other features and objects of the present invention, as well as the methods for achieving them, will become clearer and the present invention itself will become better understood by referring to the following description of the embodiments of the present invention in conjunction with the accompanying drawings.

1 is a schematic diagram of a first surface unevenness detection system made in accordance with the present invention utilizing two lenses and a polarizing beam splitter. FIG. 2 is a schematic diagram of a second surface unevenness detection system made in accordance with the present invention utilizing a single collimation lens, at least one linear polarizer, and a non-polarizing beam splitter. FIG. 3 is a schematic diagram of the system shown in FIG. 2 with an alternative arrangement in which the sensors and light sources are swapped. FIG. 4 is a schematic diagram of the system shown in FIG. 3 with an alternative arrangement in which a cylindrical lens is utilized for evaluation of a curved display module. 1 is a flow chart illustrating a method for assessing the integrity of an assessed surface according to the present disclosure. FIG. 2 is an exploded perspective view of a display module according to the present disclosure. FIG. 6B is a schematic diagram of the display module shown in FIG. 6A.

Corresponding reference symbols indicate corresponding parts throughout the drawings. The examples described herein illustrate embodiments of the invention, and the embodiments disclosed below are not intended to be exhaustive or to be construed to limit the scope of the invention to the precise form disclosed.

The present disclosure is directed to a method for inspecting and evaluating relief or other surface unevenness of a display module using Schlieren-type imaging. The test object is directly (i.e., perpendicularly) exposed to linearly polarized and collimated, incoherent light. This conditioned light signal is then reflected from a reflective surface of the test object or a reflective surface integrated into the test object. The polarization of the reflected light is rotated 90° by a double pass through a clear quarter-wave plate integrated into a polarizer stacked on the display module. The imaging camera images the reflected light signal after subjecting it to an additional polarizing filter. Because the plane of the evaluated surface of the test object is directly presented to the light signal and is parallel to the lens of the imaging camera, the evaluation image is undistorted and can therefore be sharply focused throughout the entire area to be evaluated. This in turn results in highly efficient and effective detection and quantification of relief or other unevenness.

1-4 show block diagrams of non-uniformity detection systems 10, 110, 110', 210, all of which are configured to detect surface non-uniformities, thickness variations, and/or refractive indices of transparent optical materials (e.g., cover glass or touch panels of the type used on smart phones or tablets, display cover glass, thin films, optical thin film materials, etc.). Each of systems 10, 110, 110', and 210 utilizes Schlieren imaging principles to detect surface non-uniformities caused by variations in flatness (or nominal curvature in the case of FIG. 4), thickness variations, and/or refractive index variations of transparent optical materials. The presence and extent of surface relief or non-uniformities in the surface being evaluated can thereby be detected and analyzed using non-uniformity detection systems 10, 110, 110', and 210.

Referring now to FIG. 1, the non-uniformity detection system 10 utilizes a folded Schlieren imaging system, in which a polarizing beam splitter 16 splits the light path and performs polarization switching to image the illumination profile of an object, such as a display module 50.

In particular, a non-collimated or incoherent light source 12, which may be, for example, an LED fixture, emits an incoherent light signal 30, which is then collimated by a collimation lens 14. The resulting collimated light signal 32 passes through a polarizing beam splitter to produce a P-polarized light signal 34.

The P-polarized light signal 34 is then reflected 180° by the display module 50 to produce a double-pass circular polarizer 18, which includes a quarter-wave plate and a linear polarizer. The light reflected from the linear polarizer passes in a double pass through the quarter-wave plate. In the embodiment shown, the circular polarizer 18 is integrated into the display module 50. The resulting signal reflected from the display module 50 is an S-polarized light signal 36, which re-enters the polarizing beam splitter 16 and is again reflected, this time by 90°, to become a reflected light signal 38 that remains S-polarized.

The reflected light signal 38 then passes through the collection lens 20, preserving the S-polarized signal configuration. The resulting collected light 40 is then directed to the imaging lens 22. The imaging lens has an aperture stop positioned at the focal point of the collected light signal 40. Alternatively, the aperture stop in the imaging lens can be replaced with a knife edge 22 positioned to filter the collected light signal 40 at the focal point. The resulting filtered light signal 42 is then received by the sensor 24. The sensor 24 can collect and present an image indicative of the surface evenness of the reflective surface to be evaluated. In the illustrated embodiment, the surface to be evaluated is from a display module 50, as shown and described herein.

When undulations or other unevennesses are present in the surface being evaluated, the detection system 10 causes incident light of the collected light signal 40 to be blocked by the opaque portion of the aperture stop or knife edge, while the clearly reflected light passes through the aperture stop or knife edge. In this manner, the system 10 creates a contrast change in the reflected image of the surface being evaluated as collected and output by the sensor 24 (e.g., to a monitor or other display module). This contrast change is indicative of the presence and extent of the undulations or unevennesses in the surface being evaluated, with a larger contrast change corresponding to a larger extent and/or magnitude of the undulations or other unevennesses, and vice versa.

2, a second non-uniformity detection system 110 is shown that facilitates detection and quantification of undulations or other non-uniformities in a manner similar to system 10 described above. System 110 is substantially similar to system 10 described above. The reference numerals of system 110 correspond to the reference numerals of system 10 plus 100. Elements of system 110 correspond to similar elements represented by the reference numerals of the corresponding system 10 unless otherwise noted.

However, system 110 can be reconfigured to exclude collection lens 20, thereby making system 100 physically smaller and less expensive.

In the system 110, an incoherent light source 112 emits an incoherent light signal 130, which passes through a first linear polarizer 126 to produce a P-polarized light signal 134. The light signal 134 then passes through a non-polarizing beam splitter 116 and a collimation lens 114 to produce a collimated light signal 132 that is directed perpendicular to the display module 50. That is, the collimated light signal 132 is perpendicular to the plane of the surface of the display module 50 being evaluated. The signal 132 passes in a double pass through a quarter wave plate included as part of a circular polarizer 118. The circular polarizer 118 may be configured similarly to the polarizer 18 described above.

Emanating from the display module 50, the resulting reflected light signal is an S-polarized light signal 136 oriented at 180° from the P-polarized collimated light signal 132. The signal 136 is directed back to the non-polarizing beam splitter 116, which reflects the signal 136 at 90°. The resulting reflected light signal 138 then passes through a second linear polarizer 128, and the resulting S-polarized signal strikes an imaging lens 122 with an aperture stop positioned at a focal point. As described above for system 10, this aperture stop (or knife edge) at the focal point causes any light rays reflected by non-flat portions of the reflective surface of the display module 50 to be blocked by the opaque portion of the aperture stop, thereby creating a contrast to the light rays reflected from flat surface portions. Thus, the image collected by the sensor 124 via the light signal 142 provides a contrast indication of the presence, location, and magnitude of relief or other surface unevenness in the evaluated surface of the display module 50.

Figure 3 illustrates a non-uniformity detection system 110' that is generally similar in structure and function to the non-uniformity detection system 110 described in detail above. Systems 110 and 110' are substantially similar to each other and comprise the same configuration of structures as shown.

However, detection system 110' swaps the positions of light source 112 and sensor 124 relative to beam splitter 116, along with other associated components (such as aperture stops and linear polarizers 126 and 128). As shown in FIG. 3, incoherent light source 112 emits an incoherent optical signal 130, which passes through linear polarizer 126 to produce a P-polarized optical signal 134. Signal 134 is then reflected 90° by non-polarizing beam splitter 116. The resulting reflected signal 138 passes through collimation lens 114 to produce a collimated optical signal 132, which is reflected off display module 50 via circular polarizer 118 in the same manner as described above for system 110.

The reflected S-polarized light signal emitted by the surface being evaluated of the display module 50 then passes through a non-polarizing beam splitter 116 and a second linear polarizer 128. An imaging lens (or knife edge) 122 filters the S-polarized light signal 136, and the resulting light signal 142 is received by a sensor 124. The resulting image sensed by the sensor 124 has a contrast indication of the presence and extent of surface unevenness as described above.

Referring now to FIG. 4, the non-uniformity detection system 210 has a configuration generally similar to the system 110' described above. Moreover, the system 210 is substantially similar to the systems 110 and 110' described above, and the reference numerals of the system 210 correspond to the reference numerals of the systems 110 and 110' plus 100. Elements of the system 210 correspond to similar elements represented by the reference numerals of the corresponding system 110, unless otherwise noted.

However, the non-uniformity detection system 210 further includes a cylindrical lens 215 that receives the collimated optical signal 232 from the collimation lens 214. The cylindrical lens 215 passes the P-polarized focused optical signal 240 toward the curved display module 250 that contains the circularly polarized light 218. After reflection and a double pass through the polarizer 218, the optical signal 236 reflects off the curved surface being evaluated and passes back through the cylindrical lens 215 and the collimation lens 214 to generate a reflected optical signal 238.

The convergent light signal 240 is a one-dimensional curved (i.e., focal) wavefront that is incident on a corresponding convexly curved reflective surface of the display 250. The radius of curvature of this focal wavefront is equal to the intended radius of the curved convex display surface of the display module 250. Thus, the S-polarized light signal 236 reflected by the evaluated surface of the module 250 passes back through the cylindrical lens 215 and is recollimated. It then passes back through the collimation lens 214 and is refocused towards the sensor 224 as a reflected light signal 238. The cylindrical lens thereby operates to produce a reflected light signal 238 from the curved surface of the curved display module 250. The curved display module 250 is in the same Schlieren imaging configuration as the systems 10, 110, and 110' designed for the evaluation of flat surfaces detailed above. In this way, the presence and extent of non-uniformities of the curved evaluated surface can be investigated in the same way as a flat (i.e., planar) surface.

In the embodiment shown in FIG. 4, cylindrical lens 215 is a positive (i.e., focusing) cylindrical lens designed for use with a convexly curved display as described above. However, similarly formed negative cylindrical lenses can also be designed for accurate measurement of the non-uniformity of curved convex display panels and used to generate wavefronts that extend in one dimension as well.

Figure 4 shows the light source 212 emitting a P-polarized light signal 234 via a linear polarizer 226 towards the reflective surface of the non-polarizing beam splitter 216, while the reflected light signal 238 passes through the beam splitter 216 towards the sensor 224. This configuration is similar to the system 110' shown in Figure 3 and described in detail above, except for the addition of the cylindrical lens 215 and the system 210. However, the configuration of the system 110 shown in Figure 2 can be modified in a similar manner with the addition of the cylindrical lens 215 for evaluation of the curved display module 250. That is, the light source 212 and the sensor 224 can be replaced with their associated components for the beam splitter 216.

For systems 10 and 110 shown in Figures 1 and 2, respectively, the light source 12, 112 shines directly on the display module 50. That is, the collimated beam derived from the light source 12, 112 is perpendicular to the plane defined by the surface of the display module 50 to be evaluated. For purposes of this disclosure, "substantially perpendicular" refers to approximately 90°, at least 89.5°, 89.7°, or 89.9°, or at most 90.1°, 90.3°, or 90.5°, including exactly 90°, or any range of angles defined by any pair of the aforementioned values.

In contrast, in the systems 110' and 210 shown in Figures 3 and 4, the incoherent light source 112, 212 emits incoherent light signals 130, 230 that are nominally parallel to the surface being evaluated of the display module 50 and 250, respectively, but after reflection from the non-polarizing beam splitter 116, 216 and collimation, the collimated light beam shines directly (i.e., perpendicular) on the plane defined by the surface being evaluated.

Thus, all of the systems 10, 110, 110', and 210 are positioned such that the plane defined by the lenses of the respective sensors 24, 124, and 224 is perpendicular to the incoming filtered signal 42, 142, 242, respectively. This incoming signal is a direct reflection of the reflective surface of the display module 50 or 250. The sensors 24, 124, and 224 are therefore positioned to receive a reflected collimated optical signal. The reflected collimated optical signal is a direct 180° reflection at the plane of the evaluated surface of the display module 50, 250. The resulting images generated by the sensors 24, 124, and 224 are therefore perfectly or nearly perfectly in focus. Conversely, in systems where the reflected image received by the sensor comes from a display module that is angled with respect to the sensor lens, perfect focusing is only possible by going beyond a thin strip of the reflected image.

For systems 10, 110, and 110', the surface being evaluated is substantially planar, and display module 50 presents a nominally planar display to the user. For purposes of this disclosure, "substantially planar" in the context of mobile phones and handheld tablet devices may mean a surface with a nominal variation of 100 μm or less from flatness. For these systems, contrast in the image received by sensor 24 or 124 represents non-flatness or other unevenness in the surface being evaluated.

4, on the other hand, shows a system 210 designed for the evaluation of a curved surface of a display module 250 as described above. This curved surface may be taken to define a plane of inspection similar to the flat surface of the display module 50. For the purposes of this disclosure, the plane of the evaluated surface of the curved module 250 is the plane defined by the curved surface and perpendicular to the radius of curvature that bisects the area of the surface to be evaluated. Thereby, half of the curved surface is on one side of the plane and the other half of the curved surface is on the other side of the plane. In the system 210 of FIG. 4, the image sensed by the sensor 224 represents imperfections in the curvature of the surface to be evaluated. A "perfect" surface represents a surface that perfectly conforms to the desired rounded (e.g. cylindrical or spherical) surface, and imperfections represent deviations from that perfect surface.

FIG. 5 shows an exemplary method for evaluating imperfections on a surface being evaluated, either flat (in the case of systems 10, 110, or 110') or curved (in the case of system 210). This method 300 may be performed by a user of a system made in accordance with the present disclosure, or may be automated through the use of a computer or controller.

In an embodiment, the images detected by the sensor 24, 124, or 224 are evaluated by a controller. In an embodiment, the controller is microprocessor-based and includes a non-transitory computer-readable medium. The non-transitory computer-readable medium includes processing instructions stored therein that are executable by the microprocessor of the controller to evaluate the detected images to determine the level of imperfections in the display surface under test. The non-transitory computer-readable medium, or memory, may include random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (such as EPROM, EEPROM, or flash memory), or any other tangible medium capable of storing information.

The images will be processed by software designed to detect and evaluate contrast changes, determine defect size and generate a score for the overall quality of the display. This software can be implemented using both traditional image processing and machine learning techniques.

In step 310, an incoherent optical signal is emitted, for example, by applying power to a light source. In an exemplary embodiment, the optical signal is an LED signal coming from one of the light sources 12, 112, or 212. In step 320, the incoherent optical signal passes through a beam splitter, such as polarizing beam splitter 16, or non-polarizing beam splitter 116 or 216, to create a first optical signal and a second optical signal that are angled with respect to each other. In one exemplary embodiment, the first and second optical signals may be angled 90° with respect to each other and split approximately 50:50, such that each of the first and second optical signals are equal or substantially equal in intensity. Light that passes straight through the polarizing beam splitter is linearly polarized in a first direction, referred to herein as P-polarized. In the case of a non-polarizing beam splitter, the light is not polarized by the beam splitter.

In step 330, at least a portion of the incoherent optical signal passes through a collimation lens to produce a collimated optical signal. In some systems made in accordance with the present disclosure, such as system 10, this collimation step may occur before the incoherent optical signal enters the beam splitter. In other systems made in accordance with the present disclosure, such as systems 110, 110', and 210, this step may occur after the optical signal passes through or is reflected by the beam splitter. Thus, in some cases, only a portion of the incoherent optical signal may pass through the collimation lens.

In step 340, at least a portion of the incoherent optical signal is polarized. Such polarization may be influenced by one or more structures, including polarizing beam splitter 16 in system 10, linear polarizers 126, 128 in systems 110, 110', or linear polarizers 226 and 228 in system 210. In addition, each of systems 10, 110, 110', and 210 may influence the polarization of at least a portion of the coherent optical signal, either before or after collimation, via circular polarizers 18, 118, or 218, respectively.

In step 350, the collimated light signal is reflected off a surface being evaluated, such as a reflective surface of display module 50 or 250, to produce a reflected light signal. The reflected light signal is sensed, such as by a sensor, such as sensor 24, 124, or 224, to produce a sensed image. In step 370, the sensed image is used to assess contrast to determine the presence and magnitude of non-uniformities in the surface being evaluated.

In one embodiment, the display module 50, 250 may be a mobile phone, tablet, or other handheld display device, and the system 10, 110, 110', or 210 is used to evaluate the operator interface of the mobile phone or tablet. For example, Figures 6A and 6B show a mobile phone 400 that may replace the display module 50 or 250 (depending on whether the phone 400 has a nominally flat or nominally curved user interface).

6A, the mobile phone 400 includes a back cover 410. The bottom shell 420 is connected to the face shell 430 and protects a circuit board 425 configured to provide functionality to the mobile phone 400. The bottom shell 420 is configured to support a battery 415 and is further configured to connect to the back cover 410. The face shell 430 is configured to connect to and support a display module 440. When fully assembled, the display module 440 includes a display layer 470 and a cover glass/touch panel 450a. The cover glass/touch panel 450a is configured as a transparent material or transparent optical material 450. When all of the various components are connected, the mobile phone 400 is configured in a user-friendly container suitable for handling by human hands. A tablet can be configured similarly to the phone 400, except that it has larger overall dimensions.

The display module 440 includes a display layer 470, such as a liquid crystal display (LCD), a circular polarizer 460, and an optically transparent cover glass/touch panel 450a. In some configurations, the circular polarizer 460 may be integrated into the display layer 470, as shown by the dotted outline surrounding both the display layer 470 and the circular polarizer 460. The display layer 470 is configured to provide a visual interface to a corresponding user by displaying an image viewable by the user. The display layer 470 may include one or more additional layers as needed or desired for a particular application. Various technologies are used to construct the display layer 470. Typically, the display layer 470 is configured as pixels that provide colored light viewable by the user. These technologies include liquid crystal display (LCD), light emitting diode (LED), organic light emitting diode (OLED), and the like. The cover glass/touch panel 450a is positioned adjacent to the display layer 470 or the circular polarizer 460 associated with the display layer 470. The cover glass/touch panel 450a is configured as a user interface. A user may interact with the mobile phone 400 and/or provide input control by touching the glass or panel 450a using a stylus or one or more fingers.

Other uses for the display module 440 and/or transparent optical material 450 are contemplated, such as display screens, television screens, computer monitors, tablet devices, integrated display screens (e.g., integrated into a vehicle dash, desk surface, panel, etc.), portable communication devices, etc.

In particular, uniformity of the top surface 451 of the cover glass/touch panel 450a and the top surface 471 of the display layer 470 is desirable for an optimal visual experience for a user. Embodiments of the present disclosure, including systems 10, 110, 110', and 210 described in detail above, are configured to detect and/or measure the flatness of the top surface 451 of the cover glass 450a or other transparent material, and the flatness of the top surface 471 of the display layer 470 or other reflective material.

While this invention has been described as having an exemplary design, the invention may be further modified within the spirit and scope of the disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the disclosure as come within known or customary practice in the art to which this invention pertains, and which fall within the limits of the appended claims.

Claims (19)

1. An imaging system, comprising:
an incoherent light source that emits an incoherent optical signal;
a collimation lens positioned to receive the incoherent optical signal and to emit a collimated optical signal;
a sensor having a sensor lens defining a sensor lens surface oriented substantially perpendicular to a direction of propagation of the incoherent optical signal emitted from the incoherent light source and positioned to receive a reflection of the collimated optical signal;
a polarizer disposed between the incoherent light source and the sensor;
a display module having a surface to be evaluated defining a plane of an evaluation surface, the display module positioned such that the plane of the evaluation surface is substantially perpendicular to a direction of travel of the collimated optical signal. The imaging system of claim 1, wherein the sensor lens surface is substantially parallel to the plane of the evaluation surface, and the direction of travel of the incoherent light signal is substantially parallel to the plane of the evaluation surface. The imaging system of claim 1, wherein the sensor lens surface is substantially perpendicular to the plane of the evaluation surface, and the direction of travel of the incoherent light signal is substantially perpendicular to the plane of the evaluation surface. The imaging system of claim 1, wherein the surface being evaluated is a substantially planar surface, whereby the image sensed by the sensor includes a contrast indication of non-planarity of the surface being evaluated. The imaging system of claim 1, wherein the surface being evaluated is a curved surface, and further comprising a cylindrical lens having a curvature corresponding to the curved surface, whereby the image sensed by the sensor includes a contrast indication of imperfections in the curvature of the surface being evaluated. The imaging system of claim 1, wherein the sensor lens has an aperture. The imaging system of claim 1, further comprising a beam splitter positioned to split the incoherent optical signal into a first optical signal and a second optical signal, the first optical signal being angled relative to the second optical signal. The polarizer comprises:
a first linear polarizer disposed between the incoherent light source and the beam splitter, the beam splitter comprising a non-polarizing beam splitter;
The imaging system of claim 7 further comprising a second linear polarizer disposed between the sensor and the beam splitter. The imaging system of claim 7, wherein the beam splitter and the polarizer are combined as a polarizing beam splitter. The imaging system of claim 9, further comprising a collection lens disposed between the polarizing beam splitter and the sensor. The imaging system of claim 10, wherein the sensor lens comprises one of an aperture and a knife edge. The imaging system of claim 1, wherein the incoherent optical signal is emitted by a light emitting diode. 1. A method for evaluating imperfections in an evaluated surface of a display module, comprising:
emitting an incoherent optical signal;
passing the incoherent optical signal through a beam splitter to produce a first optical signal and a second optical signal, the first optical signal being angled relative to the second optical signal;
passing at least a portion of the incoherent optical signal through a collimation lens to produce a collimated optical signal;
reflecting the collimated optical signal off the evaluated surface of the display module to produce a reflected optical signal, the evaluated surface defining an evaluation surface plane that is substantially perpendicular to a direction of propagation of the collimated optical signal;
and sensing the reflected light signal at a sensor to produce a sensed image. The method of claim 13, further comprising evaluating contrast in the sensed image to determine the presence and magnitude of surface unevenness of the evaluated surface. The surface to be evaluated is a curved surface, and the method comprises:
passing the collimated optical signal through a cylindrical lens to produce a modified collimated optical signal;
The reflecting step includes reflecting the modified collimated optical signal onto the surface being evaluated, the surface being curved;
The method of claim 14 , wherein assessing contrast comprises determining the presence and extent of imperfections in the curvature of the curved evaluated surface. the surface being evaluated is a substantially flat surface;
The method of claim 14 , wherein assessing contrast comprises determining the presence and extent of non-planarity in the substantially planar surface. The method of claim 13, further comprising polarizing at least one of the incoherent optical signal, a portion of the incoherent optical signal, and the collimated optical signal. The step of sensing the reflected light signal comprises:
passing the reflected optical signal through one of the apertures;
and passing the reflected optical signal over a knife edge. positioning the collimation lens substantially perpendicular to at least a portion of the incoherent optical signal;
The method of claim 13 , further comprising: positioning the surface to be evaluated substantially parallel to the collimation lens.