Illumination of optical monitoring device

Abstract

An apparatus for generating image data comprises an imaging device (11) for imaging a material (4) moving through an imaging region (12) and an illumination unit (10) for illuminating the imaging region. The illumination unit includes a light source (15) and a free-form lens (14) configured to refract light emitted by the light source, thereby providing uniform illumination for the imaging device in an imaging region. A free-form lens and a method for illuminating an imaging region of an imaging apparatus are also disclosed.

Description

Technical Field

[0001] The present invention relates to devices and methods for producing illumination, and more particularly to producing illumination for optical monitoring in industrial processes. Background Art

[0002] Industrial processes may involve large amounts of material moving during processing. Monitoring of the material may be required at various stages of the process. Monitoring can be carried out for various reasons and can be applied to various materials. These materials can include any material from small particulate matter to large particulate matter. Non-limiting examples of materials include food substances such as grains, legumes, nuts, fruits, vegetables, processed foods, etc., polymeric materials, metallic materials and wooden materials, composite materials, waste materials, and any other physical substances flowing in the process.

[0003] Monitoring can be used to classify and / or analyze the material. In this specification, the term sorting encompasses various material handling tasks that can be performed based on monitoring. For example, sorting can encompass any type of inspection, grading or classification, quality control, defect detection, various analyses or evaluations of the material, measuring volume, quantity, moisture, and separation between organic and inorganic materials, such as when processing waste. Other property-related parameters can also be monitored, such as color, polymer type, damaged items, etc. There are many uses for sorting, and the above examples are not an exhaustive list of sorting applications. Material analysis applications provide information on the monitored material, such as quality analysis and reporting.

[0004] Monitoring of the material can be carried out by specific optical devices configured for the classification and analysis tasks of bulk materials. Monitoring can provide surveillance based on signals from imaging devices such as digital cameras or scanners, optical readers, etc. Optical sorters typically use line scan cameras, the field of view or imaging field / area of which is usually less than a few millimeters wide and can be hundreds of millimeters long. Signals from the imaging device can be input into a data processing device for further processing and analysis. Appropriate process control actions can be taken based on this processing.

[0005] Optical devices may need to use high-power broadband visible and infrared illumination. Currently, the main types of light sources include incandescent halogen bulbs and light-emitting diodes (LEDs). Similar to most light sources, incandescent halogen bulbs have isotropic emission. The illumination and detection systems are typically arranged such that the illumination unit is close to the object to be monitored behind a glass window (transparent or frosted). Relatively low-cost LED light sources are used for visible light, and halogen lamps are used for the infrared region.

[0006] Energy-intensive halogen light sources are being phased out in favor of LEDs. To illuminate a single imaging area, hundreds of LEDs may be required. Although multiple LEDs increase the light level on the line, there are camera systems with higher resolutions that may require higher light power. Multiple LED lights may also require complex light control units and filtering devices to provide uniform illumination.

[0007] Light sources typically have almost isotropic emission, while the observation area of a line scan camera is usually less than a few millimeters wide and less than a few hundred millimeters long. To generate a high enough irradiance in such a small area, the front illumination on an optical sorter should be as close to the object as possible. Being close to the object may obstruct entry into the observation area. Dust and other dirt on the object may cause problems. In addition, moving objects may damage the equipment.

[0008] Two-dimensional concentrating optics, such as reflectors, have been used in optical sorters. The concentrating reflector enables the illumination to be located further away from the product. These reduce the required light power, but the efficiency is still very low. The illuminated area is more than three orders of magnitude larger than the camera observation area or the actual imaging area. Generating uniform illumination within the camera's observation area is also technically challenging, especially on multi-module machines.

[0009] A large amount of light power and electrical power may be wasted in this process. Some of the wasted light affects the noise level in the detection system through stray light, reflection, and scattering. The additional light power and stray light are potential health and safety hazards. The low optical efficiency of the current systems described above is particularly problematic in applications where the cost per milliwatt of light power is high, such as in the ultraviolet or infrared parts of the spectrum. High temperatures may cause problems for the materials and environment being monitored, and / or pose health and safety issues. Summary of the Invention

[0010] Aspects described herein are aimed at solving at least some of these problems.

[0011] According to one aspect, there is provided an apparatus for generating image data, the apparatus including an imaging device for imaging a material moving through an imaging area and a lighting unit for illuminating the imaging area, the lighting unit including a light source and a freeform lens configured to refract light rays emitted by the light source so as to provide uniform illumination for the imaging device in the imaging area.

[0012] According to another aspect, there is provided a freeform lens for illuminating an imaging area of an imaging device configured to generate image data of a material moving through the imaging area, wherein the freeform lens is configured to refract light rays emitted by a light source so as to provide uniform illumination for the imaging device in the imaging area.

[0013] According to another aspect, there is provided a method for optical monitoring, the method comprising imaging a material moving through an imaging region by means of a digital imaging device, emitting light from at least one light source, and refracting light rays from at least one light source onto the imaging region by means of at least one freeform lens, thereby providing uniform illumination for the imaging device in the imaging region.

[0014] According to a more specific aspect, there is provided a freeform lens that is shaped to refract illumination onto the imaging region such that uniform irradiance is provided in the imaging region.

[0015] The freeform lens can be shaped to refract illumination onto the imaging region such that the imaging device provides a uniform response with optimized efficiency in the imaging region.

[0016] The freeform lens can be shaped to compensate for detection losses in the edge region of the field of view of the imaging device by providing stronger illumination in the edge region of the imaging region.

[0017] The imaging device and the illumination unit can be mounted in a single optical monitoring unit.

[0018] The housing of the optical monitoring unit can be enclosed. The housing can be provided with an observation opening. The housing can be pressurized to prevent debris from entering the housing.

[0019] The device can include at least two illumination units. The imaging device can be located between the freeform lenses of the at least two illumination units.

[0020] The imaging device can include a line scan camera.

[0021] When the distance from the freeform lens is in the range of 150 mm to 1200 mm, the illumination unit provided with the freeform lens can be configured to irradiate a region with a width of up to 50 mm and a length in the range of 150 mm to 600 mm.

[0022] The device can include at least one freeform lens that is shaped to provide a sharp illumination cutoff at the end of the imaging region.

[0023] The device can include at least one freeform lens that is shaped to control illumination crosstalk with adjacent imaging regions and / or illumination units.

[0024] The device can include at least two illumination units for irradiating the imaging region, wherein the freeform lenses of the at least two illumination units are customized such that the sum of the illuminations from the freeform lenses of the at least two illumination units produces uniform irradiance of the imaging device or a uniform response of the imaging device on the imaging region.

[0025] The device may include a sorting device and / or an analysis device, configured to sort and / or analyze bulk materials moving through an imaging area based on image data generated by an imaging device. The device may be configured to perform at least one of inspection, grading, separation, rejection, and measurement and / or quality analysis and / or product stability analysis of the material.

[0026] The device may be configured to direct illumination onto the material exiting from a chute or conveyed by a conveyor. The material may include at least one of organic materials, food ingredients, food, granular polymer materials, wood materials, bulk dry goods, waste materials, and / or metallic materials.

[0027] According to one aspect, light from an illumination unit is directed towards the imaging area by at least one freeform lens configured to refract light rays such that the illumination is refracted in the imaging area to provide uniform irradiation in the imaging area. The illumination may also be refracted in the imaging area such that the imaging device provides a uniform response in the imaging area with optimized efficiency. A clear illumination cut-off may be provided at the end of the imaging area. The illumination crosstalk with adjacent imaging areas may be controlled. At least two illumination units may be used to provide a single uniform illumination area.

[0028] The freeform lens may include silicone.

[0029] The freeform lens may be composed of at least two optical elements. One or more refractive surfaces may be constructed within the lens. The lens may be formed from separate components. These elements may be of different materials. These elements may have different optical properties. Each element may provide at least one freeform surface. At least one optical element having at least one free surface may include materials such as glass, plastic, and / or silicone.

[0030] A computer software product may be used to design and produce the lens assemblies described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Some aspects will now be described in more detail by way of example only, with reference to the following examples and drawings, in which:

[0032] Figure 1 A side view of a schematic example of a material handling system including an optical monitoring device is shown;

[0033] Figure 2 A plan view of a schematic example of a material handling system including an optical monitoring device is shown;

[0034] Figure 3 An example of providing uniform illumination in the imaging area is shown;

[0035] Figure 4Shows an example of an optical monitoring device assembly;

[0036] Figure 5 Shows a schematic diagram of a three-dimensional freeform lens refracting light rays formed according to the principles disclosed herein;

[0037] Figure 6A and 6B Shows a perspective view of a freeform lens formed according to the principles disclosed herein;

[0038] Figure 7A and 7B Shows a plan view and a cross-sectional view of another freeform lens formed according to the principles disclosed herein;

[0039] Figure 8 Shows another example of a freeform lens;

[0040] Figure 9 Shows an operation flowchart according to an example; and

[0041] Figure 10 Shows the results of testing and simulation. Detailed Description

[0042] The following description gives an exemplary description of some possibilities for practicing the present invention. Although the specification may refer to "one", "a", or "some" examples or embodiments at several places in the text, this does not necessarily mean that each mention refers to the same example or embodiment, nor does it necessarily mean that a particular feature applies only to a single example or embodiment. Individual features of different examples and embodiments can also be combined to provide other embodiments.

[0043] Figure 1 Shows a side view of a schematic example of a material handling system 1 provided with an optical monitoring device 10, the optical monitoring device 10 being configured to generate image data of the material in the imaging area 12. An imaging device 11 is provided for imaging the material moving through the imaging area 12. The line of sight from the imaging device 11 to the imaging area 12 is represented by a dashed line 13. Figure 2 Shows a plan view of a processing system having similar functional components.

[0044] The processing system includes a chute 2 that guides the material 4 through the system as shown by the arrow 3. The chute 2 guides the downwardly moving material 4 towards the material processing device 8. Instead of or in addition to the chute, the processing system may also include a conveyor or other device for moving the material in the system. The conveyor may include, for example, a belt conveyor or another conveyor that can move the material and can be provided with an imaging area to expose the material to the imaging device.

[0045] The material handling device 8 is controlled by a controller system including a data processing device 6. The material handling device can process materials in various ways. For example, the materials may be subject to quality analysis and / or control measures, and through appropriate sorting devices, the materials can be accepted / rejected based on detected impurities, deformed objects, defects, dimensions, colors, variations, etc. Monitoring can be used to evaluate product stability. Other non-limiting examples include the grading or classification of materials, where different grades or varieties of materials are divided into different grades or categories according to control instructions from the control system. For example, food materials, other biological materials, and / or waste materials can be separated into different material streams by the material handling device 8 configured to sort materials.

[0046] The imaging device may include a digital camera 11. A specific example of the digital camera is a line scan camera. In this example, the imaging area 12 extends across the width of the material 4 that lies between the end of the chute 2 and the processing device 8. For example, the processing device 8 can provide sorting facilities.

[0047] In this specification, the term imaging area refers to the field of view of the camera on the imaging plane. In a line scan application, the imaging area includes a substantially narrow strip. Figure 3 An example of the strip-shaped imaging area 12 is shown. In a line scan application, the narrow strip is used to directly perform two-dimensional imaging on the imaging area, which can extend across the width of the material stream or only on a part of the material stream.

[0048] In Figure 1 the example, the imaging area 12 includes a narrow strip that extends across the width of the material 4 emerging from the end of the chute 2. The camera is configured to image the entire length of the narrow imaging area, thereby imaging all of the material 4 passing through the monitoring device 10. The image captured by the optical elements of the camera is converted into a digital data signal for input into the data processing device 6.

[0049] The camera 11 is connected to the data processing device 6 via a data connection 19. This connection can be any suitable wired or at least partially wireless data connection. Data can be transmitted from the camera based on any appropriate data communication protocol. The data processing device 6 can include any suitable computer device configured to perform the monitoring, analysis, and control functions required for process control. The data processing device can include any appropriate computing device that includes at least one processor, memory, software, and internal circuits, as well as components required to perform tasks configured to implement at least some of the features described herein. Figure 1Shows an example of the internal components of a data processing device arranged on a board, the device including a processor and a memory, as well as connections between the device elements and an interface for connecting the data processing device to a camera. At least one processor can be configured to execute appropriate software code to implement one or more of the following aspects. The software code can be stored in at least one memory. The data processing device 6 can be connected to a wider data communication system (such as an intranet or the Internet) / as part of it. The data processing device can be configured for monitoring and controlling large-scale production facilities, such as factories or food processing plants. For example, the data processing device can be configured for food factories, various types of food processing applications, recycling plants, different raw material processing facilities, etc. The functions of the data processor device can be provided at least partially in the cloud or in a virtualized environment. An appropriate gateway can be provided between different environments.

[0050] The optical monitoring device 10 also includes two collinear illumination units, each unit including a light source 15 and a freeform lens 14. The freeform / deformed lens can provide tailored uniform illumination. Thus, the illumination unit can adjust the illumination to irradiate an area with a limited spatial range. Figure 1 Lines 17 and 18 in it represent the extreme values of the effective light rays that emerge from the freeform lens 14 and are shaped by it to be guided to the imaging area 12 in a predetermined manner. The light energy can be utilized uniformly on the imaging area 12. The light energy can be refracted precisely towards the distal end of the imaging area while preventing the light rays from escaping from the sides of the conveyor belt 2.

[0051] To ensure uniformity along the length of the imaging area 12, the freeform lens is shaped and the light distribution can be optimized so that the light energy is uniformly distributed over the pixels in the direction of the camera's line of sight. The provided illumination area can be configured to substantially match the imaging area 12. The freeform lens can be customized to compensate for detection losses at the edges of the field of view.

[0052] The optical monitoring device can be equipped with at least one customized freeform lens such that the illumination unit can be further away from the material flow 4 while maintaining good optical power. This can provide better access for cleaning the machine. This can also simplify the design of the monitoring device.

[0053] The freeform optical principle for lens design and the possibility of designing freeform lenses will be described in more detail later in this specification.

[0054] Freeform lenses can be made of plastic. Plastic includes a variety of synthetic or semi-synthetic materials that use polymers as the main component. Plastic can be molded, extruded, and / or pressed into solid objects of various shapes. Plastic lenses can be used because low-wattage light sources, such as low-wattage LEDs, generate very little heat, allowing the use of plastic. Other materials can also be used for freeform lenses. One possibility is to make freeform lenses from silicone, or more precisely, from polymeric siloxanes or polysiloxanes. Glass can also be molded into a suitable freeform. Silicone and glass lenses are particularly good for ultraviolet (UV) and infrared (IR) applications. Silicone does not absorb UV light in the same way as plastic, so lenses made of silicone can be particularly advantageously used for fluorescence detection because their properties allow more UV light to pass through the lens.

[0055] A lighting unit equipped with a freeform lens can be designed to produce uniform illumination within the line of sight of a camera, with a clear cut-off at each end to avoid crosstalk with adjacent modules. Figure 3 Examples are shown illustrating how the illumination area 60 drawn by dotted lines can be shaped to closely follow the extreme values of the imaging area 12 drawn by solid lines. According to an example of providing a single light source to transmit light power to a section of light, the aspect ratio of the illumination area covering the imaging area 12 can be in the range of about 10:1 to 60:1. For example, the dimensions of a bar-shaped illumination area are approximately 600 mm × 10 mm or multiples thereof. According to another example, when the distance from the freeform lens can be in the range of 150 mm to 1200 mm, one or more lighting units can illuminate an area up to 50 mm wide and in the range of 150 mm to 600 mm in length. In some applications, the imaging area can be narrower than the illumination area.

[0056] The light source 15 can include, for example, one LED or multiple LEDs. Halogen or incandescent bulbs can also be used. In another embodiment, multiple bulbs can be provided.

[0057] Figure 4A schematic view of the optical monitoring device 10 is shown, in which two light sources 15, two corresponding freeform lenses 14 and a camera 11 therebetween are mounted to the frame 20 of the assembly by means of a fitting 21. The mounting of the components relative to each other can be fixed during the assembly of the unit such that the unit is ready for installation relative to the processing device. The components of the optical monitoring device can be pre-calibrated so that no or only minimal calibration is required on site. The fitting 21 can allow for fine-tuning of the unit. Thus, the foreground illumination unit can be connected to the camera via the frame, thereby jointly constituting an integrated compact monitoring or optical monitoring device. This makes the assembly easy. The light sources, lenses and camera of the device can be pre-adjusted before assembly, which can eliminate or minimize the need for on-site adjustment. Within a single module, the optical monitoring devices can be placed in sequence without interfering with each other.

[0058] It is also advantageous to mount the camera on the same axis between two illumination units, since the line of sight of the camera is well aligned with the light rays of the lenses. Collinear illumination with the camera can be used to reduce shadow artifacts.

[0059] It should be noted that the optical monitoring device does not necessarily have to include two illumination units. The optical monitoring device can include only one illumination unit or more than two illumination units. The illumination unit can include at least one freeform lens and at least one light source. Multiple light sources can be arranged linearly above the lens. Other forms are also possible. The light from multiple illumination units can overlap or add up to form uniform illumination in a single imaging area.

[0060] Figure 5 An illustrative example is shown of how light rays 50 emitted from the light source 15 are refracted by the freeform lens 14 into a carefully designed light pattern 51. The freeform or deformable lens 14 can be configured to provide customized illumination to achieve better focusing and control of light. The lens geometry can be shaped to produce different light distributions on the imaging area. Whatever design is chosen, the goal is to evenly map the light energy in the light rays onto the plane of the imaging area, i.e., in each case, the lens is designed so that the pixels on the imaging area receive a uniform amount of light. The light rays can emerge from the lens in various patterns, such as non-crossing divergent, crossing convergent, crossing divergent and / or non-crossing convergent patterns. Any of these can be used to achieve the lens design described herein.

[0061] Through careful mapping, a freeform lens design can be provided such that there is no substantial change in the amount of light received by each pixel on the imaging area, thereby enabling a good dynamic range of the optical system. Thus, uniform illumination can be achieved on the imaging area using a single light source (such as a single LED).

[0062] According to another possibility, the loss of camera lens detection at the edge of the camera lens is compensated by guiding more light energy at the edge of the imaging area, thereby providing uniformity. The lens shapes the isotropic emission of the extended-size light source and focuses the light onto a concentrated, uniform segmented-shaped illumination area. This can be used to increase the amount of light available in the camera imaging area while reducing the total energy used.

[0063] Figure 6A , 6B , 7A and 7B show examples of freeform lens designs. Figure 6A and 6B show a perspective view of a freeform lens, the shape of which can provide uniform illumination. Figure 7A and 7B show a cross-section of a freeform lens, the shape of which can provide uniform illumination. The shown freeform lens is configured to adjust the shape of one or more of its surfaces to redirect the light rays emitted from the light source in three dimensions, thereby providing the desired illumination on the image captured by the camera.

[0064] Software-assisted optimization can be used to design a freeform lens with at least one three-dimensional surface, which is customized to optimally direct the light rays to a favorable position. A semi-ellipsoid with appropriate length, width, and height can be used as the starting point of an iterative process. Information about the imaging area, the position and orientation of the ellipsoid, and the light source can be used as inputs. The software-assisted optimization algorithm can be run on a computer to iteratively form the shape of the lens surface until a shape that achieves the desired illumination in the imaging area is found. Both the input and output surfaces can be shaped. A CAD / CAM model can be created for the designed shape, and a freeform lens can be manufactured based on this model.

[0065] The lens can consist of at least two optical elements. Each element can have at least one freeform surface. For example, a multi-element freeform lens can be constructed such that two or more lens elements are glued or assembled into a lens unit. The freeform lens can be constructed to provide one or more refractive freeform surfaces within the lens, for example, by forming the lens as separate parts. These elements can be of different materials and / or can have different optical properties. For example, such a configuration can be used to compensate for chromatic aberration of a broadband light source.

[0066] Figure 8 shows an example of a freeform lens 80 including multiple optical elements. In this example, the light emitted from the light source 15 enters the first lens element 81 and then is transmitted to the second lens element 83 via the interface 82 between the elements 81 and 83.

[0067] Freeform optics is a technology that utilizes freeform surfaces (optical surfaces without linear or rotational symmetry). The properties of freeform surfaces provide a high degree of design freedom, which can be used to avoid the limitations on the lens surface geometry and create efficient designs. The design of lenses can be freed from the constraints of traditional optical surface geometries. The design methods for freeform illumination optics include zero-étendue algorithms (based on the assumption of an ideal light source) and design algorithms for extended light sources. Zero-étendue algorithms include ray mapping methods, Monge-Ampère equation methods, and the support quadratic form method (SQM). Algorithms for extended light sources include illumination optimization, feedback design, and simultaneous multi-surface methods. Using freeform surfaces can generate new designs that cannot be achieved using spherical or aspherical surfaces.

[0068] The design of freeform illumination optics can be described as follows: Given the input of a light source and the output of a lens as a specified illumination, design one or more freeform surfaces to redirect the light rays emitted by the light source to produce the specified illumination on the target surface (this is an inverse problem). To give a more detailed example, the SQM method can be used to design freeform lenses in an intuitive way. It can be assumed that the predefined illuminance distribution is a continuous function defined on a domain. The domain is pixelated, and sampling points are defined for each pixel. The energy assigned at each sampling point can be considered equal to the total energy contained in its corresponding pixel. After the domain is pixelated, the specified illumination problem is converted into a discrete illumination problem. Then the discrete illumination problem can be solved. The light rays emitted from the light source S are considered to be refracted by the i-th surface patch and converge to the point Ti on the target plane in the imaging region. The i-th surface patch is an ellipsoidal interface, and the points S and Ti are the two foci of the ellipsoid. The total energy transmitted by the i-th surface patch is determined by the parameters of this ellipsoid. With a fixed focal length, the parameters of the ellipsoid (such as the length of the major axis) can be iteratively adjusted so that the total energy transmitted by the i-th surface patch to the point Ti is equal to the specified value. For the discrete illumination problem, a set of ellipsoidal surface patches is calculated, and the number of surface patches is equal to the number of sampling points. The final freeform lens is formed by these surface patches. The SQM method can also be used to find the ray mapping of the ray mapping method.

[0069] The above are illustrative examples, and there are several possible design methods that can be used to achieve the desired freeform lens design. A more detailed description of these can be found in Wu, Rengmao, Zexin Feng, Zhenrong Zheng, Rongguang Liang, Pablo Benítez, Juan C. in Laser & Photonics Reviews 12, no. 7 (July 2018): 1700310. and in the article "Design of Freeform Illumination Optics" by Fabian Duerr.

[0070] The generation and optimization of the freeform lens shape can be accomplished with the help of software products configured specifically for this purpose. Commercially available ray tracing software can be used to evaluate the design performance between iterations. Examples of such are commercially available software products such as Speos, Lightools, Tracepro, and Zemax.

[0071] Figure 8 An example method of optically monitoring a material using a three-dimensional (3D) freeform lens is shown. The method shown includes: at step 100, emitting light from at least one light source; at step 102, refracting the light rays emitted by at least one light source in three-dimensional space through at least one freeform lens such that they are directed towards an imaging region, thereby providing uniform illumination for an imaging device in the imaging region; at step 104, imaging the material moving through the imaging region using a digital imaging device; at step 106, generating digital image data by a camera.

[0072] The image data can be used for various purposes. For example, a sorting device can be operated based on control instructions generated in response to the image data.

[0073] Figure 1 and Figure 2 A system equipped with a single optical monitoring device including a single camera is shown. The monitoring system can include multiple monitoring devices, lighting units, and cameras as well as corresponding imaging regions. These can all be connected to a control system / data processing device 6. Placing multiple high-power lighting units close to each other or at least within sight of each other may cause interference. This can be solved by shaping the freeform lens shape of the lighting unit such that the illumination is directed only within a limited spatial range to the relevant imaging region. The illumination can produce uniform light within the sight range of the camera, with a clear cut-off at each end to avoid crosstalk with adjacent monitoring modules. Crosstalk may lead to limitations in the device design and size, for example because additional lighting is required. Adjusting the shape of the freeform lens can mitigate the effects of crosstalk and / or control crosstalk such that the illumination distribution is uniform and the imaging device can see a flat illumination. The use of interactive lighting units can also be used to reduce the overall size and complexity of the system architecture.

[0074] Performance tests and simulations have been conducted on an optical monitoring system that includes two freeform lenses configured according to the principles disclosed herein. The simulation results are as Figure 9As shown, where curve 90 represents the blue band, curve 91 represents the green band, and curve 92 represents the red band. The results show that the curves are relatively stable within the imaging area, that is, the illumination is uniform between the edge areas 94 of the imaging area represented by the dashed line. In addition, a relatively obvious cut-off of each color band is detected at the edge. Below, in combination with examples, the achievable benefits will be described in more detail in the case of providing foreground illumination for a similar optical sorting device (using the illumination device described herein).

[0075] A lens with a three-dimensional (3D) freeform surface shape can improve illumination efficiency. The 3D shape of the lens can be optimized so that the irradiance at any point along the length of the camera viewing area is the same. The illumination on the imaging area can be provided in smaller segments. Using a 3D freeform lens causes the light emitted from the light source to be concentrated into segments defined within the imaging area. Generally, the illumination uniformity of the viewing area can be improved, thereby improving the accuracy of imaging and analysis results.

[0076] According to a feasible solution, a plurality of lighting units including at least one light source and a lens can be arranged to cover the length of the imaging area. By using a plurality of lighting units working together, the total power can be increased while maintaining a stable response in the area.

[0077] The lighting unit including a freeform lens and a light source can be designed according to the specific requirements of various monitoring applications. The lighting unit can be customized to convert a point light source or an extended light source into an illumination area, which can have any specific shape and / or condition that affects imaging. In applications where all the light is provided by a single light source, simple spectral and spatial illumination customization can be provided. Controlled spatial brightness can be achieved. A smaller number of LEDs means that less filtering is required, and smaller or fewer filters can be used. A system with a dispersion compensation scheme can be arranged to provide a flat spectrum in the illumination area.

[0078] A customized freeform lens can also be used to comprehensively manage the heat generated by high-power illumination. Compared with a row of light sources, a freeform lens can reduce the number of light sources required to achieve the same final image plane irradiance. Reducing the heat can also avoid failures caused by overheating. For safety and product quality reasons, reducing the generated heat is important. Reducing the heat generated within the lighting component and / or the lighting unit housing is an important advantage.

[0079] The lighting unit that generates foreground illumination can be placed at a point farther from the material being monitored. This can allow the use of a smaller window or even eliminate the need for a window in front of the monitoring unit.

[0080] According to one possible solution, the optical monitoring unit may be provided with an observation opening instead of using a glass window or the like, and at the same time, a positive air pressure is set inside the housing of the optical monitoring unit, so that the air flowing out of the observation opening prevents dust from entering the housing. The advantage of this is that during operation, there is no problem that the glass or similar window may break and / or get dirty.

[0081] Adding a freeform lens in front of the light source can reduce the need for cleaning and the impact on the classification of dust and debris in the material flow. The spraying system may be located very close to the imaging area, resulting in more dust and flying objects near the optical system. These can clutter the optical window. It may be necessary to wipe it several times per hour, reducing the overall production capacity. Dust also changes the camera's recognition of the material appearance. The freeform lens allows the lighting unit to be positioned farther away from the imaging area, thus reducing the amount of dust and substances that may fall on the glass or other optical devices. This can reduce the need for cleaning. In addition, the freeform lens provides easier access to the optical device, so cleaning can be done more quickly if needed.

[0082] The modularity of the detection unit allows for a more compact design and / or a more flexible arrangement of the view of the material. It can relieve the limitations caused by separate lighting devices including multiple light sources. The modular design can be customized to be compatible with different sizes and types of machinery and processes without additional space filling, thus reducing the footprint of the device. When multiple areas need to be viewed, the modular system can eliminate or reduce problems because the differences between the end and intermediate units can be minimized, avoiding crosstalk between modules. The monitoring system can consist of compact modular units that allow viewing at different points and angles along the material flow path.

[0083] The amount of stray light that may interfere with other vision systems can be reduced or even eliminated. Better control of light radiation can be used to alleviate optical safety problems. The effective dynamic range of detection is increased. Flat illumination can be provided and the reduced sensitivity of the camera at high angles can be compensated. Reduced cost, complexity, and energy consumption can be provided.

[0084] Placing the camera near or between the lenses can reduce the shadow of the image. This may result in better results, especially when imaging large objects, because the shadow effect can be alleviated. For example, when imaging broccoli, holes inside can be seen.

[0085] It should be noted that although the above detailed examples are described with reference to certain processes, applications, and devices, several variations and modifications can be made to the disclosed solutions without departing from the scope of the present invention. In particular, different embodiments have been described as examples. Different features from different embodiments can be combined.

[0086] The foregoing description has provided a complete and informative description of exemplary embodiments of the present invention by way of example and not limitation. However, various improvements or modifications may be apparent to those skilled in the relevant art in view of the foregoing description when taken in conjunction with the accompanying drawings and the appended claims. All such and similar modifications taught by the present invention will fall within the scope of the present invention.

Claims

1. An apparatus (10) for generating image data, comprising: an imaging device (11) for imaging a material (4) moving through an imaging area (12), and a lighting unit for irradiating the imaging area, the lighting unit comprising a light source (15) and a freeform lens (14), the freeform lens being configured to refract light emitted by the light source so as to provide uniform illumination for the imaging device over the imaging area.

2. The apparatus according to claim 1, wherein the freeform lens (14) is shaped to refract illumination over the imaging area (12) to provide uniform irradiance over the imaging area, and / or the freeform lens (14) is shaped to refract illumination over the imaging area (12) such that the imaging device (11) provides a uniform response with optimized efficiency over the imaging area.

3. The apparatus according to claim 1 or 2, wherein the freeform lens (14) is shaped to compensate for detection losses in an observation edge region of the imaging device (11) by stronger illumination at an edge region of the imaging area (12).

4. The apparatus according to any one of the preceding claims, wherein the imaging device and the lighting unit are mounted in a single optical monitoring unit.

5. The apparatus according to any one of the preceding claims, comprising at least two lighting units, wherein the imaging device is located between the freeform lenses of the at least two lighting units.

6. The apparatus according to any one of the preceding claims, wherein the imaging device comprises a line scan camera.

7. The apparatus according to any one of the preceding claims, wherein the lighting unit provided with the freeform lens is configured to irradiate an area having a width of up to 50 mm and a length in the range of 150 mm to 600 mm when the distance from the freeform lens is in the range of 150 mm to 1200 mm.

8. The apparatus according to any one of the preceding claims, comprising: at least one freeform lens (14) shaped to provide a clear illumination cut-off at an end of the imaging area, and / or at least one freeform lens (14) shaped to control illumination crosstalk with an adjacent imaging area and / or lighting unit.

9. The device according to any one of the preceding claims, comprising at least two illumination units for illuminating an imaging area (12), wherein, The freeform lenses of the at least two lighting units are customized such that the sum of the illuminations from the freeform lenses of the at least two lighting units produces uniform irradiance over the imaging area or a uniform response of the imaging device.

10. The apparatus according to any one of the preceding claims, comprising a sorting device and / or an analysis device (1) configured to sort and / or analyze bulk material (4) moving through the imaging area (12) based on image data generated by the imaging device (11).

11. The apparatus according to claim 10, configured to: perform at least one of inspection, grading, separation, rejection, measurement, quality analysis, and / or product stability analysis on the material based on the image data generated by the imaging device, and / or Direct the illumination to the material (4) emerging from the chute (2) or carried by the conveyor, the material (4) comprising at least one of organic materials, foodstuffs, food, granular polymeric materials, wood materials, bulk dry goods, waste and / or metallic materials.

12. A freeform lens (14) for illuminating an imaging area (12) of an imaging device (11), the imaging device (11) being configured to generate image data of a material (4) moving through the imaging area (12), wherein, The freeform lens (14) is configured to refract the light emitted by the light source (15) so as to provide uniform illumination for the imaging device over the imaging area.

13. The freeform lens according to claim 12, comprising: At least two optical elements providing at least one freeform surface; and / or At least one optical element having at least one freeform surface comprising glass, plastic and / or silicone.

14. A method for optical monitoring, comprising: Imaging the material (4) moving through the imaging area (12) by means of a digital imaging device (11); Emitting light (16) from at least one light source (15); and Refracting the light from the at least one light source into the imaging area by means of at least one freeform lens (14) so as to provide uniform illumination for the imaging device over the imaging area.

15. The method according to claim 14, comprising directing the light to the imaging area (12) by means of the at least one freeform lens, the at least one freeform lens being configured to refract the light such that at least one of the following is achieved: The illumination is refracted over the imaging area (12) such that uniform irradiance is provided over the imaging area; The illumination is refracted over the imaging area (12) such that the imaging device (11) provides a uniform response with optimized efficiency over the imaging area (11); A sharp illumination cut-off is provided at the end of the imaging area; The illumination crosstalk with adjacent imaging areas is controlled; and / or At least two lighting units provide a single uniform illumination area.

Images