阅读说明：本技术 杂散光测试站 (Stray light test station ) 是由 C.D.卢 M.T.D.里内哈特 J.C.F.王 M.沙加姆 于 2020-03-26 设计创作，主要内容包括：用于杂散光测试站的方法、系统及装置。在一个方面,所述杂散光测试站包含：照明组合件,包含：空间延伸光源；及一个或多个光学元件,被布置为将来自所述空间延伸光源的光束沿光学路径引导至光学接收器组合件,所述光学接收器组合件包含透镜容器,所述透镜容器被配置为接纳透镜模块并将所述透镜模块定位于抛物面镜下游的所述光学路径中,使得所述透镜模块将来自所述空间延伸光源的光束聚焦至图像平面；及可移动框架,其支撑所述光学接收器组合件,所述可移动框架包含一个或多个可调整对准载台以相对于所述照明组合件定位所述光学接收器组合件,使得所述照明组合件的光学路径在所述光学接收器组合件的视场内。(Methods, systems, and apparatus for a stray light test station. In one aspect, the stray light test station includes: an illumination assembly, comprising: a spatially extended light source; and one or more optical elements arranged to direct the light beam from the spatially extended light source along an optical path to an optical receiver assembly comprising a lens receptacle configured to receive a lens module and position the lens module in the optical path downstream of a parabolic mirror such that the lens module focuses the light beam from the spatially extended light source to an image plane; and a movable frame supporting the optical receiver assembly, the movable frame including one or more adjustable alignment stages to position the optical receiver assembly relative to the illumination assembly such that an optical path of the illumination assembly is within a field of view of the optical receiver assembly.)

1. A stray light testing apparatus comprising:

an illumination assembly comprising a spatially extended light source and one or more optical elements arranged to direct a light beam from the spatially extended light source along an optical path, the illumination assembly comprising a parabolic mirror arranged in the optical path, wherein a diameter of the light beam at the parabolic mirror is larger than a lateral dimension of the parabolic mirror;

an optical receiver assembly comprising a lens receptacle configured to receive and position a lens module in the optical path downstream of the parabolic mirror such that the lens module focuses a light beam from the spatially extended light source to an image plane; and

a movable frame supporting the optical receiver assembly, the movable frame comprising one or more adjustable alignment stages, wherein the adjustable alignment stages position the optical receiver assembly relative to the illumination assembly such that the optical path of the illumination assembly is within a field of view of the optical receiver assembly.

2. The apparatus of claim 1, wherein the parabolic mirror is an off-axis parabolic mirror.

3. The apparatus of claim 2, wherein the off-axis parabolic mirror is off-axis by 30 °, 60 °, or 90 °.

4. The apparatus of claim 1, wherein the light beam from the spatially extended light source is apodized to form a uniform beam across a diameter.

5. The apparatus of claim 1, wherein the spatially extended light source is adjustable over a range of angles.

6. The apparatus of claim 5, wherein the spatially extended light source has an angular extent of 0.5 ° degrees.

7. The apparatus of claim 1, wherein the one or more optical elements further comprise one or more neutral density filters.

8. The device of claim 1, wherein the light beam from the illumination assembly is allowed to reach the optical receiver assembly.

9. The device as recited in claim 1, further comprising a control unit in data communication with the illumination assembly and optical receiver assembly and operable to perform operations to perform a stray light test.

10. The apparatus of claim 1, wherein the sensor is a CMOS camera.

11. The apparatus of claim 1, wherein the lens container comprises a pressurized clamp.

12. The apparatus of claim 1, wherein the optical receiver comprises an adjustable receptacle configured to receive and position a camera module in the optical path downstream of the parabolic mirror such that the light beam from the illumination assembly is focused to an image plane at the camera module.

13. The apparatus of claim 1, wherein the adjustable alignment stage is adjustable in one or more dimensions to position the optical receiver assembly over a range of angles.

14. A method for determining stray light performance of an optical receiver assembly, comprising:

aligning the optical receiver assembly in an optical path downstream of an illumination assembly including a parabolic mirror using one or more adjustable alignment stages, wherein aligning the optical receiver assembly comprises focusing a light beam from a spatially-extended light source of the illumination assembly to an image plane of a sensor of the optical receiver assembly;

selecting a first light intensity of the spatially extended light source from a plurality of different light intensities;

exposing the optical receiver assembly to light from the spatially-extended light source at the first light intensity;

capturing image data by the sensor of the optical receiver assembly when the optical receiver assembly is exposed to light at the first light intensity; and

determining a performance metric of the optical receiver assembly based on the captured image data.

15. The method of claim 14, wherein selecting the first one of the plurality of light intensities from the spatially extended light source comprises attenuating the light beam from the spatially extended light source using a neutral density filter.

16. The method of claim 14, wherein determining stray light performance of the optical receiver assembly further comprises determining stray light performance of the optical receiver assembly at a plurality of angles of incidence of the spatially extended light source within a field of view of the optical receiver assembly.

17. The method of claim 14, wherein the parabolic mirror is an off-axis parabolic mirror.

18. The method of claim 14, wherein the beam from the spatially extended light source is apodized to form a uniform beam across a diameter.

19. The method of claim 14, wherein the spatially extended light source is adjustable over a range of angles.

20. The method of claim 14, wherein aligning the optical receiver assembly comprises adjusting the adjustable alignment stage in one or more degrees of freedom to position the optical receiver assembly over a range of angles.

Background

This description relates to stray light performance of cameras. Stray light generally refers to unwanted light in the optical system and generally negatively impacts system performance. For example, in a camera system, stray light may reduce the signal-to-noise ratio in the sensors of the system and/or may reduce the contrast ratio. In many applications involving the use of optical systems to monitor outdoor environments, the sun is a significant source of stray light.

Disclosure of Invention

This specification describes technologies relating to a stray light test station to characterize performance of a camera under stray light conditions.

In general, one innovative aspect of the subject matter described in this specification can be embodied in a stray light testing device that includes: an illumination assembly including a spatially extended light source and one or more optical elements arranged to direct a light beam from the spatially extended light source along an optical path, wherein the illumination assembly includes a parabolic mirror arranged in the optical path, and wherein a diameter of the light beam at the parabolic mirror is greater than a lateral dimension of the parabolic mirror. The stray light testing device also includes an optical receiver assembly including a lens receptacle configured to receive and position a lens module in the optical path downstream of the parabolic mirror such that the lens module focuses the light beam from the spatially extended light source to an image plane. A movable frame supports the optical receiver assembly, wherein the movable frame includes one or more adjustable alignment stages, and wherein the adjustable alignment stages position the optical receiver assembly relative to the illumination assembly such that an optical path of the illumination assembly is within a field of view of the optical receiver assembly.

Other embodiments of this aspect include corresponding methods and computer programs, encoded on computer storage devices, configured to perform the actions of the methods.

These and other embodiments may each optionally include one or more of the following features. The parabolic mirror may be an off-axis parabolic mirror, wherein the off-axis parabolic mirror is off-axis by at least 30 °, at least 60 °, or at least 90 °. The sensor of the optical receiver assembly may be, for example, a Complementary Metal Oxide Semiconductor (CMOS) camera. In some implementations, the adjustable alignment stage can be adjusted in one or more dimensions to position the optical receiver assembly over a range of angles. The lens container may be a compression fixture (compression fixture) to hold the lens module in place. In some embodiments, the one or more optical elements further comprise one or more neutral density filters.

In some implementations, the optical receiver assembly includes an adjustable receptacle configured to receive and position a camera module in the optical path downstream of the parabolic mirror such that the light beam from the illumination assembly is focused to an image plane at the camera module.

In some embodiments, the light beam from the spatially extended light source is apodized to form a uniform beam across a diameter. The spatially extended light source may be adjustable over an angular range, and may have an angular range of 0.5 ° degrees. The light beam from the illumination assembly is allowed to reach the optical receiver assembly, such as during a stray light test of the optical receiver assembly.

In some implementations, the stray light test station further includes a control unit in data communication with the illumination assembly and the optical receiver assembly and operable to perform operations to perform stray light testing.

In general, another innovative aspect of the subject matter described in this specification can be embodied in methods for determining stray light performance of an optical receiver assembly, the method including: aligning the optical receiver assembly in an optical path downstream of an illumination assembly including a parabolic mirror using one or more adjustable alignment stages, wherein aligning the optical receiver assembly includes focusing a beam from a spatially-extended light source of the illumination assembly to an image plane of a sensor of the optical receiver assembly; selecting a first light intensity of the spatially extended light source from a plurality of different light intensities; exposing the optical receiver assembly to light from the spatially-extended light source at the first light intensity; capturing image data by the sensor of the optical receiver assembly when the optical receiver assembly is exposed to light at the first light intensity; and determining a performance metric of the optical receiver assembly based on the captured image data.

These and other embodiments may each optionally include one or more of the following features. In some implementations, determining stray light performance of the optical receiver assembly further includes determining stray light performance of the optical receiver assembly at a plurality of angles of incidence of the spatially-extended light source within a field of view of the optical receiver assembly.

In some embodiments, selecting the first light intensity of the plurality of light intensities from the spatially extended light source comprises attenuating the light beam from the spatially extended light source using a neutral density filter.

Particular embodiments of the subject matter described in this specification can be implemented to realize one or more of the following advantages. An advantage of the present techniques is that they can be used to calibrate stray light performance of a camera assembly including a lens and sensor(s), such as a CMOS sensor. In particular, the performance of the camera assembly can be measured under stray light conditions by illuminating the camera assembly using a spatially extended source at infinity, for example, to simulate the illumination conditions of the sun, high beams, etc. The apparatus may be used to simulate conditions under which a camera is illuminated by a variety of different light sources, e.g., high intensity light sources (such as the sun), infrared sources, hyperspectral sources, etc. Simulating various stray light illumination conditions can help to develop, for example, the rejection ratio of the camera assembly to improve camera performance under exposure conditions that include stray light sources. The stray light test station may be adjustable to accommodate various lens types to accommodate rapid evaluation of different shaped lenses, for example, from different manufacturers.

The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

Drawings

Fig. 1 is a block diagram of an example of an illumination assembly of a stray light test station.

FIG. 2 is a block diagram of an example of a receive assembly of the stray light test station.

FIG. 3 is a block diagram of an example of a stray light test station.

FIG. 4 is a schematic diagram of an example of an optical receiver assembly of the stray light test station.

FIG. 5 is a schematic diagram of an example of a lens fixture of an optical receiver assembly.

Fig. 6 is a schematic diagram of an example of an optical receiver assembly.

FIG. 7 is a flow chart of an example process for performing a flare test using a flare test station.

Detailed Description

SUMMARY

The technology of the present patent application is a stray light test station for characterizing the performance of a camera under stray light conditions. Techniques utilize a spatially extended light source imaged at infinity to measure the effect of stray light on the camera and generate a rejection ratio (rejection ratio) for the camera.

More specifically, the techniques incorporate a spatially extended light source to characterize the stray light performance of the camera, for example, to simulate the operation of the camera when the sun or another high intensity light source falls within the field of view of the camera. The angular range of the spatially extended light source may be selected within a range (e.g., 0.1 ° degrees to 5 ° degrees). For example, the angular range of the spatially extended light source may be selected to simulate when the sun is within the field of view of the camera, e.g., an angular range of 0.5 ° degrees may be selected to simulate the angular range of the sun when viewed from the earth.

The test station includes: light sources, including high intensity lamps (e.g., 6500k sources, infrared 850nm sources, hyperspectral sources, etc.); an off-axis parabolic mirror; and two rotating stages for adjusting the incident angle of the spatially extended light source at the camera. The light source is configured such that a light beam emitted from the light source overilluminates (overfill) a lens of the camera to ensure uniformity of the light beam and reduce edge effects. Additionally, an off-axis parabolic mirror may be arranged to accommodate a light beam from the light source whose directional height is not parallel to the optical axis of the camera, wherein the parabolic mirror may be more than 15 ° degrees off-axis (e.g., 30 ° or more, 60 ° or more, or such as 90 ° off-axis).

The rejection ratio may be determined using a stray light testing station by measuring the effect of extended light sources on the performance of a camera sensor (e.g., on a CMOS sensor) with various Neutral Density (ND) filters used to attenuate the extended light sources. The impact of an extended light source on the performance of a camera sensor can be classified by a measurement metric as, for example, the spread of light from the center point of the light source. In some embodiments, the spread of light from the center point of the light source may be characterized as a radial spread of light from the center point of the light source.

Stray light test station

Fig. 1 is a block diagram 100 of an example of an illumination assembly 102 of a stray light test station. The illumination assembly 102 includes an optical element 104 that shapes and/or filters the light from the light source to present a spatially extended light source at infinity to the optical system under test. The optical element 104 includes a liquid light pipe 122 to receive light from the light source 120 and direct the light beam 106 from the light source along an optical path 108 to a receiver assembly including the optical system under test.

The optical element 104 additionally includes focusing optics 103 (e.g., a lens) that focuses light emitted from the light pipe 122 to an aperture provided by the aperture 116. The light beam 106 diverges from the aperture 116 before being collimated by the parabolic mirror 110 (which also reflects the light beam toward the receiver assembly). Parabolic mirror 110 is positioned in a diverging beam at a point where the diameter 112 of beam 106 at parabolic mirror 110 is greater than the lateral dimension (lateral dimension)114 of parabolic mirror 110. As such, the light beam 106 overilluminates the parabolic mirror 110, which the parabolic mirror 110 serves to apodize the light beam by directing only a central portion of the light beam toward the receiver assembly. As a result, the illumination assembly 102 delivers a collimated beam of substantially uniform intensity across its entire diameter to the receiver assembly, presenting a spatially extended light source at infinity to the receiver assembly from the perspective of the imaging system of the receiver assembly. For example, the diameter of the light beam exiting the illumination assembly can range from about 1mm to about 100mm (e.g., from about 1mm to about 50mm, from about 1mm to about 20mm, from about 1mm to about 10mm, from about 1mm to about 5mm), among others. In some examples, the beam diameter is 38.1mm (1.5 inches). The intensity of the light beam exiting illumination assembly 102 may vary by less than 50% (e.g., 30% or less, 20% or less, 10% or less, 5% or less) across its diameter.

The parabolic mirror may have a focal length range, wherein the focal length may depend in part on the angle of the incident light from the light source and the optical element 104 and the distance between the optical element 104 and the parabolic mirror 110. The focal length of the parabolic mirror 110 is chosen such that a fan of light from the light source and optics 104 overilluminates the aperture of the parabolic mirror. The focal length of the parabolic mirror 110 may range from 3 inches to 15 inches, for example. In one example, the beam diameter is 1.5 inches and the focal length of the parabolic mirror is 6 inches. In another example, the beam diameter is 3 inches and the focal length of the parabolic mirror is 12 inches.

Parabolic mirror 110 may be an off-axis parabolic (OAP) mirror. For example, the axis of symmetry of a parabola corresponding to the surface shape of the mirror is not coaxial with a central ray through the focal point of the mirror on the axis of symmetry. The degree to which the OAP mirror is displaced from the axis of symmetry can be characterized by the angle subtended by the central ray before and after reflection from the mirror. The OAP mirror 110 may be 15 ° or more off-axis (e.g., 30 ° or more, 60 ° or more, such as 90 ° off-axis). Additionally, an aperture 116 may be positioned at the focus of the OAP mirror 110.

In general, the material of the respective optical element 104 is selected based in part on the wavelength range of light tested using the stray light test station. For example, the optical element 104 may be selected for optimal performance for a broad band of 450nm to 20 μm, 650nm to 1050nm for visible wavelengths of 350nm to 750nm and/or near infrared wavelengths.

The optical element 104 additionally includes a filter(s) 118 between the aperture 116 and the mirror 110. In some implementations, the aperture 116 is a fixed aperture to set the spot size of the light beam 106 exiting the light source 120 via a light guide (e.g., liquid light pipe 122). In one example, the aperture 116 has a diameter determined by

d＝2f tan 0.25°d＝2f tan 0.25° (1)

Where d is the diameter of the aperture and f is the focal length of the parabolic mirror 110. The diameter d of the aperture may range, for example, from 1mm to 10 mm. In some embodiments, the diameter of the aperture is adjustable such that the diameter d of the aperture can be adjusted during the flare testing process.

The filter 118 is an optical filter to modify the transmitted light. Filter 118 may be, for example, a Neutral Density (ND) filter, a bandpass filter, an interference filter, a dichroic filter, an absorption filter, and so forth. In some embodiments, the plurality of filters 118 is included in an adjustable filter wheel, wherein a particular filter 118 of the plurality of filters 118 may be positioned within the path of the light beam 106. In one example, a plurality of ND filters 118 (e.g., ND filters having respective Optical Densities (OD)0, 1, 2, 3,4, 5, and 6) may be selected such that the light beam 106 may be adjusted to have a variable intensity within a range of light output intensities.

Generally, the light source 120 is selected to provide light having a spectral composition and intensity suitable for simulating a stray light source of the optical system under test. Broadband, narrowband, or monochromatic sources are possible. In some embodiments, the light source 120 can be, for example, a Light Emitting Diode (LED) broad spectrum source (e.g., having a color temperature of 6500K or warmer, e.g., 2700K to 3000K, 3500K to 4100K, or 5000K to 6500K), a xenon lamp, an infrared 850nm source, a hyperspectral source, or the like.

Other variations are also possible. For example, although the liquid light pipe 122 directs the light beam 106 from the light source 120 to the optical element 104, other light guides may be used. For example, in some embodiments, the light beam 106 may be directed from the light source 120 via a fiber optic bundle. The liquid light pipe 122 may be positioned relative to the optical element 104 such that the cone of light from the light beam 106 overilluminates the parabolic mirror 110. In a particular embodiment, free-space optics are used to direct light from the light source to the optical element 104. In a particular embodiment, the light source 120 is positioned adjacent to the optical element 104 such that the light beam 106 from the light source 120 is directed to the optical element 104.

In some implementations, a plurality of light sources 120 can be included in the illumination assembly 102, wherein one or more liquid light pipes 122 can be positioned to direct light from respective ones 120 of the plurality of light sources 120 to the optical element 104. For example, the illumination assembly 102 may include 6500k LED light sources and infrared 850nm light sources, with each light source having a respective liquid light pipe 122 that is interchangeable to direct a selected light source 120 into the optical element along the optical path 108. The light source 120 may be a hyperspectral light source, for example, a multi-LED light source that includes a range of wavelengths (e.g., for characterizing the performance of a camera module and/or lens module within a range of wavelengths (e.g., near infrared to ultraviolet wavelengths)).

Illumination assembly 102 can provide a spatially extended light source at infinity for a beam width in the range from 25mm to 100mm in diameter along optical path 108. The optical element 104 may be used to direct a spatially extended light source at infinity to direct the light beam 106 along an optical path 108 to an optical receiver assembly of a stray light test station, as described below with reference to fig. 2.

Fig. 2 is a block diagram 200 of an example of an optical receiver assembly 202 of a stray light test station. The optical receiver assembly 202 includes a lens receptacle 204 that may be adapted to receive a lens module 205 and position the lens module 205 such that the lens module focuses a light beam 206 along an optical path 208 to an image plane 210. The image plane 210 may correspond to the sensor 212, where the sensor 212 captures a two-dimensional (2D) image of the light beam 206 focused on the image plane 210. The sensor 212 may be, for example, a Complementary Metal Oxide Semiconductor (CMOS) sensor, a Charge Coupled Device (CCD) sensor, a photomultiplier tube, or a photodiode.

The optical receiver assembly 202 may utilize the natural divergence of the light beam 206 from the illumination assembly rather than using optical components to shape the light beam 206 upstream of the parabolic mirror of the illumination assembly. The amount of angular beam divergence of the light beam 206 at the optical receiver assembly 202 depends in part on the angular extent of the extended source (e.g., ± 0.25 ° degrees), where the extent of angular beam divergence depends on the focal length f and the aperture diameter d as determined by equation (1).

The optical receiver assembly 202 includes a lens clamp 214 that holds the lens module 205 when the lens module 205 is received by the lens container 204. Lens container 204 includes a plurality of dimensions (e.g., length and inner diameter) selected based in part on the dimensions of lens module 205 tested using the flare test station. Further details of lens container 204 are discussed below with reference to fig. 6.

The lens clip 214 may be a compression clip to hold the lens module 205 in place and allow for easy insertion and removal of the lens module 205 in the optical receiver assembly 202. Lens clamp 214 includes a plurality of dimensions (e.g., inner diameter of window, length of compression screw) selected based in part on the dimensions of lens module 205 tested using the stray light test station. Further details of lens holder 214 are described with reference to fig. 5.

Although depicted as separate components for receiving the lens receptacle 204 and the sensor 212 of the lens module 205 with reference to fig. 2, the optical receiver assembly 202 may alternatively include an adjustable receptacle that receives and positions a camera module in the beam 206 along the optical path 208 such that the beam 206 is focused to an image plane at the camera module. The camera module may include an assembled lens and sensor device, where the lens of the camera module is attached to the sensor to focus the light beam 206 on an imaging plane of the sensor in the camera module.

The materials of the elements (e.g., lens receptacle 204 and lens holder 214) included in the optical receiver assembly may be selected based in part on ease of manufacturing, compatibility with the material of lens module 205, and/or reducing stray light effects. The material may include metal (e.g., aluminum or steel) and plastic (e.g., acetal) material). The elements included in the optical receiver assembly may be coated with a paint or similar substance (e.g., a matte black paint layer) or have a black anodized surface (e.g., black anodized aluminum) to reduce stray light effects.

The optical receiver assembly 202 includes a movable frame 215 that supports the optical receiver assembly 202 in the stray light testing station. The movable frame 215 includes one or more adjustable alignment stages 216a, 216 b. The adjustable alignment stages 216a, 216b may be attached to each other by supports 218 (e.g., L-shaped brackets, corner brackets, etc.).

The adjustable alignment stages 216a, 216b position the optical receiver assembly 202 relative to the light beam 206 along the optical path 208 from the illumination assembly (e.g., from the illumination assembly 102 of fig. 1). The optical receiver assembly 202 is positioned using the adjustable alignment stages 216a, 216b such that the optical path 208 is within the field of view of the optical receiver assembly 202. Adjustable alignment stages 216a, 216b can be, for example, a rotational alignment stage, a pitch/tilt (tip/tilt) alignment stage, a translation XYZ stage, or another similar stage that provides multiple degrees of freedom of movement to position optical receiver assembly 202 relative to optical path 208. The adjustable alignment stages 216a and 216b may be adjusted independently of each other and may provide a yaw and roll to change the angle of incidence of the optical path 208 to the lens module 205.

In some implementations, the movable frame 215 supporting the optical receiver assembly 202 can be adjusted over a range of incident angles, for example, by adjusting the position of the optical receiver assembly relative to the optical path 208 within the field of view 207 of the lens module 205. The range of incident angles may be, for example, ± 90 ° degrees with respect to the vertical and/or horizontal axes of the lens module 205. The range of incident angles may be defined by the field of view of the lens module 205. The particular range of incident angles may depend in part on the field of view of the lens module 205. For example, lens module 205 may be a wide angle lens module such that the performance of lens module 205 and sensor 212 under stray light conditions needs to be tested over a range of incident angles (e.g., where the field of view of the wide angle lens module is 180 degrees). In some embodiments, the movable frame 215 including the adjustable alignment stages 216a, 216b is a motorized alignment stage that can be positioned by a control unit that operates the motorized alignment stage. The motorized alignment stage may include various motors, such as piezoelectric motors, servo motors, linear motors, stepper motors, and the like.

Fig. 3 is a block diagram 300 of an example of a stray light test station 302. The housing 304 encompasses an illumination assembly 306 (e.g., the illumination assembly 102 described in fig. 1) and an optical receiver assembly 308 (e.g., the optical receiver assembly 202 described in fig. 2). The housing 304 may be made of a metal (e.g., aluminum, steel, etc.) or plastic material and may be coated with a non-reflective or low-reflectivity layer (e.g., matte black paint). The enclosure 304 may completely enclose the stray light test station 302 to reduce exposure from ambient light below a threshold (e.g., reduce ambient light below 90%).

As depicted in fig. 3, the illumination assembly 306 and the optical receiver assembly 308 are arranged at a 90 ° angle relative to each other, with the OAP mirror 310 of the illumination assembly 306 being 90 ° off-axis. Illumination assembly 306 and optical receiver assembly 308 can alternatively be positioned at different angles relative to each other (e.g., at an angle greater than 15 ° degrees) by utilizing OAP mirrors 310 having different off-axis angles (e.g., 15 ° degrees or more off-axis).

Light beam 312 is directed by OAP mirror 310 from illumination assembly 306 along optical path 314 into field of view 316 of optical receiver assembly 308. The adjustable alignment stages 318a, 318b may be used to adjust an angle of incidence 320 of the optical path 314 relative to the optical receiver assembly 308 (e.g., adjust an angle of incidence 320 of a spatially-extended light source on a lens module or camera module of the optical receiver assembly 308).

Optical receiverSensor 322 of assembly 308 (e.g., sensor 212 of optical receiver assembly 202 described in fig. 2) may be positioned along optical path 314 at a distance 324 from parabolic mirror 310 such that the radial angular range of parabolic mirror 310 of illumination assembly 306 is 10^-4And 10^-5Within the stray halo of (a). Distance 324 scales with the diameter of parabolic mirror 310, for example, distance 324 may be in the range of 0.5 meters to 3 meters. In one example, selected to implement 10^-4And 10^-5The angular extent of the stray halo parabolic mirror 310 is less than 1.5 degrees. In one example, sensor 322 is positioned at a distance 324 from parabolic mirror 310900 mm such that the angular range of parabolic mirror 310 is 1.2 degrees.

Depending in part on the distance 324 between the parabolic mirror 310 and the optical receiver assembly 308, the space-extended source at infinity provided by the illumination assembly 306 may have an angular range ranging from 0.1 ° degrees to 5 ° degrees. In one example, the distance 324 between the parabolic mirror 310 and the optical receiver assembly 308 is such that the spatially extended source at infinity has an angular range of 0.5 degrees.

In some embodiments, the distance 324 may be adjusted by the adjustable alignment stages 318a, 318 b. In one example, optical receiver assembly 308 can be moved further away from or closer to parabolic mirror 310 by translational movement of alignment stage 318 b.

Stray light test station 302 includes a controller 326 that operates the light source of illumination assembly 306 (e.g., may control the intensity of the light source, turn the light source on/off, etc.). The controller 326 may additionally control automated functionality of the stray light testing station 302, including, for example, an automated filter wheel to select a filter (e.g., filter 118) and/or to adjust the alignment of the optical receiver assembly 308 by operating electrically adjustable alignment stages 318a, 318 b.

In some embodiments, the controller 326 includes a data collection module 328. The data collection module 328 may be in data communication with the sensor 320 or camera module of the optical receiver assembly to receive imaging data 330 from the sensor 320 of the optical receiver assembly 308. For example, the imaging data 330 may be a two-dimensional image of the light beam 312 as collected by the sensor 320 at an imaging plane of the sensor 320. The controller 326 and data collection module 328 may be subcomponents of a computer, mobile device (e.g., mobile phone, tablet computer, etc.), or the like that may provide control instructions 327 and record details related to the stray light testing system 302.

In some implementations, the controller 326 includes a flare test application to receive collected imaging data from the data collection module 328 and to determine performance metrics of the lens module 332 (e.g., lens module 205), the sensor 320, or the camera module of the optical receiver assembly 308. Determining the performance metric is discussed in further detail below with reference to fig. 7.

Fig. 4 is a schematic diagram 400 of an example of an optical receiver assembly 402 of a stray light test station. As described above with reference to the optical receiver assembly 202 depicted in fig. 2, the optical receiver assembly 402 includes a lens receptacle 404 to receive a lens module 405 held in place by a lens clamp 406. The dimensions (e.g., length 407) of the lens container 404 are selected to position the lens module 405 at a distance from the sensor 408 such that the light beam 410 along the optical path 412 from the illumination assembly is focused at the image plane of the sensor 408.

The optical receiver assembly 402 additionally includes a movable frame 414, the movable frame 414 including adjustable alignment stages 416a, 416b attached by supports 418. The adjustable alignment stages 416a and 416b may be the same type of alignment stage (e.g., both are rotation stages) or each a different type of alignment stage (e.g., where 416a is a rotation stage and 416b is a translation XYZ stage). In one example, alignment stages 416a and 416b are rotating stages that control the deflection and roll of optical receiver assembly 402 and control the angle of incidence of light beam 410 at lens module 405.

Although the frame 414 is depicted in fig. 4 as having two adjustable alignment stages 416a and 416b, the frame 414 may include more or fewer adjustable alignment stages (e.g., one alignment stage or three alignment stages) to adjust the position of the optical receiver assembly 402 relative to the optical path 412 and the illumination assembly.

Fig. 5 is a schematic diagram of an example 500 of a lens fixture 502 of an optical receiver assembly (e.g., the optical receiver assembly 202 and the optical receiver assembly 402). The lens holder 502 includes an attachment point 504 to a lens container 506. Lens clamp 502 includes a lens cover 508 that is pressed against lens module 510 by compression screw 512 to hold lens module 510 fixed within lens container 506. The lens cover 508 may be fabricated (e.g., milled) from an acetal material or another plastic to reduce damage to the lens module 510 and have improved wear properties with repeated use. Compression screw 512 may be selected to prevent over-tightening of lens cover 508 over lens module 510 to reduce chromatic aberration of lens module 510 due to distortion of lens module 510. Compression screw 512 may include, for example, a low torque stainless steel M3 screw end or another similar material and thread count and a compatible nut for tightening lens cover 508 over lens module 510.

The lens cover 508 is attached to the hinge 514, wherein the lens cover 508 can pivot on the hinge 514 from an open position (to, for example, receive the lens module 510) to a closed position (to, for example, secure the lens module 510 in place). In one example, the hinge 514 allows the lens cover 508 to pivot up to 90 ° degrees or more relative to the surface of the mounted lens module 510 in the lens container 506. The inner diameter 516 of the lens cover 508 may be selected, in part, to be larger than the outer diameter of the input aperture of the lens module 510 and the inner diameter 516 may be made to be in a diameter range of, for example, 5mm to 100 mm. The inner surface 518 of the lens cover 508 is depicted in fig. 5 as a flat circular disk that lies flush with the outer surface 520 of the lens module 510. In some implementations, the lens cover 508 can include a counterbore or another surface feature (e.g., a gasketed feature) to accommodate the position of the lens module 510.

In some implementations, the lens holder 502 includes one or more adjustment points to move the lens module 510 along its optical axis relative to the position of the sensor (e.g., sensor 408). One or more adjustment points of lens holder 502 may be used to align the back focal length of lens module 510 with the sensor position.

Fig. 6 is a schematic diagram of an example of an optical receiver assembly 602a, 602b, where each optical receiver assembly 602a, 602b is configured to receive a respective lens module 604a and 604 b. Lens modules 604a, 604b may each have different operational and physical characteristics (e.g., focal length, physical size, field of view, etc.). The physical dimensions of the lens module may include a barrel length of the lens module, multiple diameters of the lens module across the barrel length of the lens module, different threads, or other attachment mechanisms. The lens module diameter may vary between, for example, 14.9mm and 50 mm. The total length of the lens module may vary between 48mm and 91.5mm, for example. The field of view of the lens module may vary, for example, by 90 degrees to define a hemispherical field of view.

In some embodiments, the lens module may have a diameter of less than 14.9mm or greater than 50mm and a length of less than 48mm or greater than 91.5 mm. The stray light test station may be adjustable to accommodate lens modules of varying sizes and varying focal lengths, for example, by adjusting the fixed position of a sensor (e.g., sensor 212) on an alignment stage (e.g., alignment stage 216 a).

The different operational and physical characteristics of each lens module 604a, 604b may require a different lens container 606a and 606b, respectively, so that each lens module 604a and 604b may be housed in an optical receiver assembly by a respective lens container. Lens containers 606a and 606b may each include a plurality of components, such as a lens barrel 608, a sleeve 610, and a Printed Circuit Board (PCB) base 612. The optical receiver assemblies 602a, 602b additionally include a lens holder 613 (e.g., lens holder 502 described in fig. 5). Each of the multiple components of the lens containers 606a, 606b and lens clamps 613a, 613b may be selected to accommodate the operational and physical characteristics of the respective lens modules 604a, 604b mounted to the optical receiver assemblies 602a, 602 b.

For clarity of discussion, details of the optical receiver assembly 602a including components of the lens container 604a and the lens holder 613a are discussed in greater detail herein, wherein the details provided may apply to the lens container 604b and the lens holder 613b, and more generally, to a given optical receiver assembly including a lens container and a lens holder mounted to a given lens module in the optical receiver assembly.

Lens barrel 608 and sleeve 610 are selected for inclusion in optical receiver assembly 602a based in part on the particular physical and operational characteristics of lens module 604 a. The dimensions of barrel 608, sleeve 610, and PCB base 612, including length, inner and outer diameters, and mounting accessories, may be selected to position lens module 604a relative to optical receiver assembly 602a such that the imaging plane of lens module 604a overlaps with sensor 614 when lens module 604a is mounted in optical receiver assembly 602 a.

The dimensions of barrel 608 and sleeve 610 are selected such that sleeve 610 is slip fit into barrel 608 and wherein a portion of lens module 604a is received by sleeve 610 and secured by sleeve 610 when the lens module is installed in optical receiver assembly 602 a. The size of the lens barrel 608 (e.g., barrel length 607) may be selected based on the total length of the mounted lens module 604 a. For example, for lens module 604a having a total length (e.g., between 48mm and 91.5 mm), barrel length 607 of barrel 608 may be 48mm to 91.5 mm. The size of the inner diameter of the sleeve 610 may be selected based on the outer diameter of the lens module. For example, for a lens module 604a having an outer diameter of between 14.9mm and 50mm over the section of the lens module in which the sleeve 610 is to be secured, the sleeve 610 will have an inner diameter of between 14.9mm and 50 mm.

The dimensions of PCB base 612 may depend in part on the physical and operational characteristics of lens module 604a and the characteristics of sensor 614. For example, the inner diameter of PCB base 612 is selected to accommodate the outer diameter of lens module 604a passing through the inner diameter of PCB base 612. PCB base 612 may be selected based in part on the dimensions of the sensor components (e.g., the height, width, and length of the sensor components on sensor 614 and the dimensions of the sensor base of sensor 614). The PCB base 612 may include threaded holes (e.g., two M6 threaded holes) along a bottom surface of the PCB base 612 for mounting the assembled optical receiver assembly 602a to a frame (e.g., the frame 414 as described above in fig. 4).

The lens container 606a, including the barrel 608, sleeve 610 and PCB base 612, may be assembled using threaded hole or through hole mounting and/or adhesive (e.g., cyanoacrylate or other similar adhesive) between corresponding elements of the lens container 606 a. For example, sleeve 610 may be slip fit inside barrel 608 and adhered using a few drops of cyanoacrylate adhesive. The lens clamp 613a may be mounted to the lens container 606a by screws (e.g., M4 screws) inserted from the lens clamp 613a into corresponding threaded holes on the lens barrel 608. Lens barrel 608 may be mounted to PCB base 612 by screws (e.g., M5 screws) inserted from PCB base 612 into corresponding threaded holes on lens barrel 608.

The sensor 614 may also be selected to be compatible with a particular lens module 604 a. The sensor 614 may be selected, for example, to include a number of pixels, a size/density of pixels, a range of sensitivity, a range of wavelengths, and so forth. Sensor 614 is mounted to PCB base 612 using, for example, through holes in threaded holes of sensor 614 into the PCB base such that sensor 614 is aligned with the imaging plane of lens module 604 a.

The components of the optical receiver assemblies 602a, 602b are generally selected to create a light-tight system such that light entering the optical receiver assemblies 602a, 602b is limited to light from the illumination assembly (e.g., illumination assembly 306).

In some implementations, varying materials, thicknesses, and transmission/reflection properties of the protective glass cover of the lens module can produce stray light effects of the lens module, which can be measured using the stray light test station described herein.

Example procedure for stray light testing

FIG. 7 is a flow chart of an example process 700 for characterizing the performance of a lens module under stray light conditions with a stray light test station.

The optical receiver assembly is positioned relative to the illumination assembly such that an optical path of the illumination assembly is within a field of view of the optical receiver assembly (702). As described above with reference to fig. 3, in stray light testing station 302, optical receiver assembly 308 is aligned with optical path 314 of light beam 312 (e.g., a spatially extended light source) from illumination assembly 306. Alignment may be performed using one or more adjustable alignment stages 318a, 318b to position the field of view 316 of the lens module 332 within the optical path 314 and cause the lens module 332 to form an image plane on the sensor 322.

The enclosure 304 may be arranged to enclose the stray light testing station 302 such that the ambient light exposure to the sensor 322 is reduced by a threshold amount (e.g., by 90% or more). Baseline or dark measurements may be used as a reference prior to beginning the testing process, for example, to establish a baseline signal-to-noise ratio for the sensor 322.

A particular light intensity of a plurality of possible light intensities from a light source (e.g., spatially extended light source 312) is selected (704). The particular light intensity may be selected using, for example, an ND filter or another form of beam intensity attenuation. In one example, an ND filter having an optical density value of 4.0 may be used to attenuate the light intensity. In another example, the light intensity may be attenuated using an ND filter having an optical density value of 1.0. In yet another example, the light intensity may be attenuated by adjusting the light source power by 5% or more, 50% or more, or 75% or more, etc.

The optical receiver assembly is exposed to a particular light intensity of the spatially extended light source (706). The optical receiver assembly 308 may be exposed to the spatially extended light source 312 by turning on the light source (e.g., light source 120). In some implementations, the spatially extended light source from the illumination assembly 306 can be exposed to the optical receiver assembly 308 by opening a shutter (e.g., opening the aperture 116), removing a beam stop (e.g., as part of the filter wheel 118), or another deflection of the light beam 312.

Imaging data of the spatially extended light source is captured by the optical receiver assembly when the optical receiver assembly is exposed to the light source at a particular intensity (708). The light exposure incident on the sensor 322 of the optical receiver assembly 308 can be, for example, a few seconds. Imaging data 330 may be captured by sensors 322 and collected by data collection module 328. Imaging data 330 may include pixels that measure the relative intensity of stray light versus a two-dimensional image of sensor 322.

After collecting imaging data of a particular light intensity, the light beam 312 may be blocked from reaching the optical receiver assembly 308, for example, using a shutter or other deflection method. The next light intensity of the multiple intensities of light may be selected to be tested, for example, using a different filter 118 and/or dimming the intensity of the light source 120. For example, an optical density 3.0ND filter 118 may be inserted into optical path 314 using a filter wheel of illumination assembly 306 to reduce the light intensity of the light source.

Data relating to a particular light intensity (e.g., a particular ND filter used or a decrease in the intensity of a light source) may be communicated to the data collection module 328 for incorporation with collected imaging data 330 of a particular light intensity as metadata. In some embodiments, the metadata includes the wavelength(s) of light being tested, and the characteristics of lens module 332 and/or sensor 322 under test using stray light test station 302.

Several different light intensities from the plurality of possible light intensities are measured (710) by a process as described in steps 702 to 708 above. The plurality of light intensities may be measured by attenuating the intensity of the light source and/or reducing the exposure of the sensor 322 using a plurality of calibrated ND filters each having a different optical density value. The number of different light intensities to be measured may be, for example, 4 or more than 4 different light intensities, 2 or more than 2 different light intensities, etc. For example, if an ND filter with an optical density value of 5.0 is used to capture a relative intensity of 1, then a range of light sources at relative intensities equal to 10-4 and 10-5 of the unattenuated light sources can be measured using ND filters with optical intensities (OD)1.0 and OD 0.0, respectively.

For the optical receiver assembly, a performance metric is determined from the imaging data (712). After each intensity of the plurality of intensities is exposed to the optical receiver assembly 308 including the lens module 332 and the sensor 322, a performance metric is determined based on the captured image. The performance metric characterizes performance of the camera under stray light conditions (e.g., a glare spread function).

The performance of the camera can be quantified by a rejection ratio, which measures the radial extent of light below the ratio of the raw source intensities using, for example, a plurality of reduced intensities of the spatially extended light source 312. The rejection ratio calculates the range of light sources having an intensity above a specified relative intensity over a two-dimensional (2D) image captured by the sensor 322. In the example presented above with reference to step 710, multiple calibrated ND filters may be used to attenuate the intensity of the light source and/or reduce the exposure of the sensor 322 to use 5.0 of lightND filters of optical density values to capture the relative intensity of 1, such that 10, equal to a non-attenuated light source, can be measured using ND filters with optical intensities (OD)1.0 and OD 0.0, respectively^-4And 10^-5The relative intensity of the light source. The range of the source in the 2D image is then measured as the radius of the farthest range from the center point of the source. The rejection ratio measurement can be used to define the Extended Source Rejection Ratio (ESRR).

In some implementations, the performance of the camera can be quantified by a glare diffusion function that describes the spatial effect of the spatially extended light source on the lens module 332 and the sensor 322, where stray light causes the light source to diffuse at high intensity over the sensor 322. Light intensities of multiple orders of magnitude are measured by, for example, attenuating the light source using multiple ND filters with different optical densities. An image is captured at each attenuated light intensity and a plot of relative intensity versus camera pixel is generated.

The performance metric determined based on process 700 may be used to compensate for stray light conditions of the camera on the vehicle at nominal operating conditions. For example, the performance metric may be used to compensate for glare from the sun when the sun is within the field of view of the camera. In another example, the performance metric may be used to compensate for saturation of the camera caused by the infrared light source (e.g., when a LIDAR system of an autonomous or semi-autonomous vehicle utilizes an 850nm light source in LIDAR detection).

The performance of various components of the optical receiver assembly (e.g., lens module, housing, PCB base, sensor, etc.) can be analyzed to isolate the source of stray light at particular angles. The stray light performance of the optical receiver assembly can be improved by utilizing design choices (e.g., lens redesign, coatings/materials, surface blackening, additional blocking of optical components, etc.).

In some embodiments, the angular range may be measured using the process 700 described above. For example, the alignment of the optical receiver 308 of the stray light testing station 302 may be adjusted to position the optical path 314 at different angles of incidence 320 relative to the field of view 316 of the lens module 332 under test. In some implementations, adjusting the angle of incidence of the optical path to the field of view of the lens module can be performed by using one or more rotating stages 318a, 318b of the optical receiver assembly 308.

In some embodiments, the performance of the camera under stray light conditions for multiple light sources may be tested by the stray light test station 302. For example, the light source 120 as described with reference to fig. 1 may include a plurality of different light sources, e.g., a broadband 6500k source and an infrared 850nm source may be incorporated into the light source 120, where each light source may in turn be used in the illumination assembly 102, e.g., where a liquid light pipe 122 may be adjusted to direct light from different light sources into the optical element 104 or a different liquid light pipe 122 (e.g., compatible with the particular wavelength(s) of the light source 120) may be used for each light source 120 to direct the utilized light source 120 into the optical element 104.

In some embodiments, a stray light test station may be used to measure the chromatic aberration of the lens and how the chromatic aberration may produce stray light effects in the lens module and/or the camera module.

In some embodiments, the stray light testing station may include a hyperspectral light source to measure the wavelength dependence of stray light effects on the lens module and/or the camera module.

Although described above with reference to fig. 1-6 as a fixed illumination assembly and an adjustable optical receiver assembly, in some embodiments, the optical receiver assembly is fixed in place while the illumination assembly may be positioned on multiple axes. In some embodiments, the illumination assembly and the optical receiver assembly can each be positioned on respective axes relative to one another.

Embodiments of the subject matter and the operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Embodiments of the subject matter described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a computer storage medium for execution by, or to control the operation of, data processing apparatus.

The computer storage media may be or may be embodied in a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Further, although the computer storage medium is not a propagated signal, the computer storage medium can be a source or destination of computer program instructions encoded in an artificially generated propagated signal. The computer storage medium may also be or may be included in one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices).

The operations described in this specification may be implemented as operations performed by data processing apparatus on data stored on one or more computer-readable storage devices or received from other sources.

The term "data processing apparatus" encompasses all kinds of apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, a system on a chip, or a plurality or combination of the foregoing. The apparatus can comprise special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them. The apparatus and execution environment may implement a variety of different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures.

A computer program (also known as a program, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform actions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing actions in accordance with the instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such a device. Further, the computer may be embedded in another device, e.g., a mobile telephone, a Personal Digital Assistant (PDA), a mobile audio or video player, a game player, a Global Positioning System (GPS) receiver, or a portable storage device (e.g., a Universal Serial Bus (USB) flash drive), to name a few. Devices suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example: semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, embodiments of the subject matter described in this specification can be implemented on a computer having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other kinds of devices may also be used to provide for interaction with the user; for example, feedback provided to the user can be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and input from the user may be received in any form, including acoustic, speech, or tactile input. Further, the computer may interact with the user by sending and receiving documents to and from the device used by the user; for example, by sending a web page to a web browser on the user's user device in response to a request received from the web browser.

Embodiments of the subject matter described in this specification can be implemented in a computing system that includes a back end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front end component (e.g., a user computer having a graphical user interface or a web browser through which a user can interact with an implementation of the subject matter described in this specification), or any combination of one or more such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include a local area network ("LAN") and a wide area network ("WAN"), an internetwork (e.g., the internet), and a peer-to-peer network (e.g., an ad hoc peer-to-peer network).

The computing system may include a user and a server. A user and server are generally remote from each other and typically interact through a communication network. The relationship of user and server arises by virtue of computer programs running on the respective computers and having a user-server relationship to each other. In some embodiments, the server sends data (e.g., HTML pages) to the user device (e.g., for the purpose of displaying data to and receiving user input from a user interacting with the user device). Data generated at the user device (e.g., a result of the user interaction) may be received at the server from the user device.

Although this specification contains many specific implementation details, these should not be construed as limitations on the scope of any features or possible claims, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In some cases, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. Moreover, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing may be advantageous.