Distance measurement using field of view

Abstract

An optical sensor. The optical sensor includes a light source (303), a first light sensor (301) and a second light sensor (302), and a controller. The light source (303) has an illumination field (313). The first light sensor and the second light sensor have corresponding first fields of view (311) and second fields of view (312). The intersection of the illumination field and the first field of view forms a first overlap region (321). The intersection of the illumination field and the second field of view forms a second overlap region (322). When a surface (304) is within one or both of the first overlap region and the second overlap region, the surface reflects light from the light source to the corresponding light sensor. The controller is configured to determine a first distance measurement to a surface within one or both of the first overlap region and the second overlap region based on a ratio of reflected light from the light source received by the first sensor to reflected light from the light source received by the second sensor. A similar ultrasonic sensor is also disclosed.

Description

Technical Field

[0001] The present invention relates to optical or ultrasonic sensors, in particular optical or ultrasonic sensors for measuring distances. Background Art

[0002] Optical proximity sensors measure the amount of light reflected from an object to determine if the object is within a specified area. Figure 1 The simple proximity sensor shown comprises a light source 101 and a light sensor 102, wherein the light source's field of illumination 111 overlaps the light sensor's field of view 112. An object 103 having a surface within the overlap region 113 will reflect light 114 back to the light sensor, providing a measurable signal.

[0003] Typically, when an object is closer to the sensor, it will produce a stronger signal. However, the strength of the signal also depends on the reflectivity of the object and its orientation (e.g., whether the sensor receives diffuse or specular reflections), so this simple sensor cannot be used to determine the position of objects within the overlap region 113 with any useful accuracy.

[0004] A plurality of such sensors can be combined to obtain coarse distance information, for example as disclosed in US Pat. No. 8,862,271 B2 and as Figure 2 As shown. The system shown includes a single light sensor 201 with a field of view 211 and two light sources 202, 203 with corresponding illumination fields 212, 213. The light sensor and light sources are arranged so that the overlap area 221 between the first illumination field and the sensor's field of view is different from the overlap area 222 between the second illumination field and the sensor's field of view. By causing the light sources to emit at different frequencies, or pulsing them at different times, or similar means, the system can determine whether a surface is present in the first overlap 221 or the second overlap 222, thereby giving a very rough distance estimate (i.e., whether the surface is within the distance range D1 corresponding to the first overlap, or within the distance range D2 corresponding to the second overlap). The system is in principle scalable to any number of overlapping regions (by providing appropriately arranged sensors and light sources), but achieving fine-grained accuracy would require an impractical number of components.

[0005] More sophisticated sensors can determine an accurate distance for any object (assuming the object reflects at least some light back to the sensor) via a "time of flight" mechanism (i.e., measuring the time difference between a pulse emitted by a light source and a pulse received by a light sensor). However, such systems are electronically complex and tend to consume significantly more power than the simpler devices described above.

[0006] Therefore, there is a need for an optical proximity sensor that has the ability to accurately measure distance but without the complexity involved in a time-of-flight sensor. Summary of the invention

[0007] According to a first aspect of the present invention, an optical sensor is provided. The optical sensor includes a light source, a first light sensor, a second light sensor, and a controller. The light source has an illumination field. The first light sensor and the second light sensor have corresponding first and second fields of view. The intersection of the illumination field and the first field of view forms a first overlapping area. The intersection of the illumination field and the second field of view forms a second overlapping area. When the surface is within one or both of the first overlapping area and the second overlapping area, the surface reflects light from the light source to the corresponding light sensor. The controller is configured to determine a first distance measurement to the surface within one or both of the first overlapping area and the second overlapping area based on a ratio of reflected light from the light source received by the first sensor to reflected light from the light source received by the second sensor.

[0008] The controller can also be configured to:

[0009] Apply modulation to the light source;

[0010] determining a second distance measurement to the surface based on a time of flight of reflected light from the light source to the first sensor;

[0011] If at least one of the first distance measurement or the second distance measurement is below a threshold distance, the first distance measurement is output, and if at least one of the first distance measurement or the second distance measurement is above the threshold distance, the second distance measurement is output.

[0012] According to a second aspect, an optical sensor accessory is provided. The optical sensor accessory comprises the optical sensor according to the first aspect and an optical time-of-flight sensor. The optical time-of-flight sensor comprises a third light sensor, another light source, and a time-of-flight system, the time-of-flight system being configured to determine a second distance measurement to a surface based on a time of flight of light emitted by the another light source, reflected by the object, and received by the third light sensor. The controller of the first aspect is further configured to output the first distance measurement if at least one of the first distance measurement or the second distance measurement is below a threshold distance, and to output the second distance measurement if at least one of the first distance measurement or the second distance measurement is above the threshold distance.

[0013] According to a third aspect, there is provided a method of operating an optical sensor according to the first aspect. The method comprises determining a distance to a surface within one or both of a first overlap region and a second overlap region based on a ratio of reflected light from a light source received by the first sensor to reflected light from a light source received by the second sensor.

[0014] According to a fourth aspect of the present invention, an ultrasonic sensor is provided. The ultrasonic sensor includes an ultrasonic source, a first ultrasonic sensor, a second ultrasonic sensor, and a controller. The ultrasonic source has a target field. The first ultrasonic sensor and the second ultrasonic sensor have corresponding first and second fields of view. The intersection of the target field and the first field of view forms a first overlapping area. The intersection of the target field of view and the second field of view forms a second overlapping area. When the surface is within one or both of the first overlapping area and the second overlapping area, the surface reflects the ultrasound from the ultrasonic source to the corresponding ultrasonic sensor. The controller is configured to determine a first distance measurement to the surface within one or both of the first overlapping area and the second overlapping area based on the ratio of the reflected ultrasound from the ultrasonic source received by the first sensor to the reflected ultrasound from the ultrasonic source received by the second sensor.

[0015] According to a fifth aspect, there is provided a method of operating an ultrasound sensor according to the first aspect. The method comprises determining a distance to a surface within one or both of a first overlap region and a second overlap region based on a ratio of reflected ultrasound from an ultrasound source received by the first sensor to reflected ultrasound from the ultrasound source received by the second sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A simple optical proximity sensor according to the prior art is shown;

[0017] Figure 2 Another optical proximity sensor according to the prior art is shown;

[0018] Figure 3 An exemplary optical sensor is shown;

[0019] Figure 4 Another exemplary optical sensor is shown;

[0020] Figure 5 Shown are included such as Figure 3 An exemplary optical sensor system of an optical sensor and a time-of-flight optical distance sensor;

[0021] Figure 6 Yet another exemplary optical sensor is shown; and

[0022] Figure 7 An exemplary ultrasonic sensor is shown. DETAILED DESCRIPTION

[0023] Figure 3An example optical sensor is shown as will be described in more detail below. The optical sensor comprises a first light sensor 301 and a second light sensor 302 and a light source 303. The light sensors and the light source are arranged such that a field of view 311 of the first light sensor overlaps with an illumination field 313 of the light source in a first overlap region 321, and a field of view 312 of the second light sensor overlaps with an illumination field 313 of the light source in a second overlap region 322. Figure 3 In the case shown, the first overlap region is a strict subset of the second overlap region, but this is not necessarily the case - there will be areas where the first overlap region intersects the second overlap region, but the first overlap region may have sub-regions outside the second overlap region and vice versa.

[0024] An object 304 having a surface within the two overlapping regions will generate a signal R at the first sensor. 1 , and generates a signal R at the second sensor 2 . R 1 and R 2 Each of these will depend primarily on the area of ​​the surface within each region, the reflectivity of the surface, and the intensity of the light source. 1 / R 2 (and its inverse) will not depend on the reflectivity or other surface properties of the surface (assuming it is uniform, which is a good approximation for small areas in most cases), as this will cancel out. Therefore, this ratio (or its inverse) can be used (with suitable calibration) to determine the distance between the optical sensor and the surface.

[0025] Although Figure 3 The illumination field and each field of view are shown as cone-shaped areas of the same orientation, but this is not necessarily the case. The illumination field and field of view can have any shape, as determined by the light source and light sensor used and any other optical components such as lenses or apertures, and they can be oriented in any suitable way to achieve the desired overlap area (as described in more detail later).

[0026] Figure 4 An alternative example is shown in which the overlap region has no intersection between the sensor and the object being detected (although they will intersect outside the object). Unless otherwise stated, reference numerals correspond to Figure 3 The overlapping region 421 between the first field of view 411 and the illumination field 412 does not intersect with the overlapping region 422 between the second field of view 412 and the illumination field. Figure 3 The same principle described in 1999 still works here - by acquiring the signal R from the corresponding sensor 1 and R 2 The ratio of φ(t) to φ(t) can be obtained, from which a value of the distance to the object 404 can be derived (via suitable calibration).

[0027] The orientation of the light sources and light sensors may be chosen in any reasonable orientation such that a) there is a corresponding overlap region that is the intersection of the field of view of each light sensor and the illumination field of the light source, and b) there is a range of distances from the light sensors where both overlap regions exist. Within this distance range, the optical sensors will be able to detect reflected light based on the ratio R of the reflected light received at each sensor. 1 / R 2 To determine the distance to the surface. Outside this distance, where R 1 is 0 and R 2 is non-zero (i.e., the ratio is zero), the sensor will be able to determine that the surface is within a distance range where the second overlap region exists but the first overlap region does not. Similarly, at R 2 is zero and R 1 When R is non-zero (i.e., the ratio is infinite), the surface is in the region where the first overlap region exists but the second overlap region does not exist. 1 and R 2 If both are zero (i.e. the ratio is indeterminate), then there is no surface in either overlap region.

[0028] The light source should also not be in the field of view of any light sensor, ie the sensor should only receive light from the light source via reflections from objects within the overlap region.

[0029] The light sources and sensors may emit and detect light of any suitable wavelength (or range or combination of wavelengths), so long as the light sensors are sensitive to at least a portion of the light emitted by the light sources. Modulation of the light emitted by the light sources (e.g., pulsing the light sources) may be used to allow the signal to be distinguished from ambient light, such as by taking a reading from each sensor when the light source is off, and subtracting that reading from the signal received by the sensor when the light source is on.

[0030] The above-described device can in principle be constructed on any scale. 1 / R 2Determining distance relies in part on the relative uniformity of reflectivity across the surface, thus improving accuracy on a smaller scale. Thus, particular applications of the device include close-range distance measurement, for example, an optical sensor as described above could be included on earbuds to detect how far they have been inserted into the ear (allowing the audio output to be adjusted to ensure the best listening experience), or included on wearable electronic devices to distinguish between a device being worn and a device in a charging base, etc. Such close-range applications are particularly problematic for existing time-of-flight sensors, which have difficulty accurately measuring distances less than 20mm (while the device described above has in principle no minimum distance, assuming the sensor and light source are properly aligned). Longer range applications include use in robotic vacuum cleaners or other autonomous mobile devices within buildings to detect steps and other "cliffs". The use of one or more such sensors can also be used to implement "gesture" control of a device, for example, activating a function if a surface (such as a hand) is waved at a specific distance from the sensor, or has a specific movement pattern.

[0031] The above device is particularly useful at distances less than 100mm, because the optics required to ensure a narrow field of view and illumination beyond that distance are complex, which reduces the advantage of the device over a time-of-flight based mechanism. In view of this, and in view that time-of-flight sensors are unreliable at short distances (e.g., less than 50mm), a combination sensor including both an optical distance sensor as described above and a time-of-flight sensor may be used.

[0032] In one example, if Figure 5 As shown, a first set of light sources and sensors may be used by a time of flight sensor 501, and a second set of light sources and two sensors may be used by an optical distance sensor 502, as described above. The sensors of the optical distance sensor are arranged so that the two overlapping regions of the optical distance sensor cover the desired sensing area to at least a first distance D, and the light sources and sensors of the time of flight sensor are arranged so that the overlap between their fields of view and illumination fields covers the desired sensing area to at least exceed the distance D. A controller (not shown) receives signals from all sensors, and if the time of flight sensor 501 indicates that the distance to the object is less than D (or does not return a usable reading), the controller uses the reading from the optical distance sensor 502. Alternatively or in addition, the controller may be configured to check the reading of the optical distance sensor 502, and if the optical distance sensor 502 indicates that the distance is greater than D, or does not return a usable reading, use the distance measurement from the time of flight sensor 501. In either case, the effect is that the controller determines the distance based on the signal from the optical distance sensor 502 for distances less than D, and determines the distance based on the signal from the time of flight sensor for distances greater than D (up to the maximum range of the time of flight sensor). Although Figure 5 The sensors and sources for the time of flight sensor 501 are shown to either side of the sensors and sources for the optical distance sensor 502, but these may be any suitable arrangement.

[0033] In such Figure 6 In the second example shown, a single set of light sources 601 and sensors 602, 603 is shared by a time-of-flight sensor 611 and an optical distance sensor 612 as described above. For example, the time-of-flight sensor 611 can determine the distance from the signal received by the sensor 602 due to the light reflected from the light source 601, and can control the light source to apply appropriate modulation to achieve the time-of-flight distance measurement. At the same time, the optical distance sensor 612 can determine the distance from the signals received from the sensors 602 and 603 due to the light reflected from the light source 601, and make appropriate corrections to account for any modulation performed by the time-of-flight sensor. As previously described, the controller 613 determines the final distance measurement by using the results from the optical distance sensor below a specified distance threshold and the results from the time-of-flight sensor above the threshold.

[0034] Where a "controller" is mentioned above, this may be implemented as any suitable combination of hardware and software, such as an ASIC, a general purpose processor running code suitable for performing the required functions, etc. The controller need not be a single device, and may include an array of cooperating devices or an array of individual processors, memory elements within a device, etc. Where control functions are attributed to other elements (e.g., to the time of flight sensor 611), this is for ease of understanding of the overall method, and these control functions may be integrated into the controller, or such other elements performing those functions may be considered to be part of the "controller".

[0035] Although a system with two sensors has been described above, additional sensors may be used, with the ratio of different sensor pairs used to validate distance measurements, or to provide improved sensitivity at different distances.

[0036] Where the above description refers to "light", this should be considered to include visible light, infrared light and ultraviolet light.

[0037] Similar systems can be used with ultrasound instead of light, such as Figure 7 As shown. The ultrasonic sensor includes a first ultrasonic sensor 701, a second ultrasonic sensor 702, and an ultrasonic source 703. The ultrasonic sensor and the ultrasonic source are arranged so that the field of view 711 of the first ultrasonic sensor overlaps with the target field 713 of the ultrasonic source in a first overlapping area 721, and the field of view 712 of the second ultrasonic sensor overlaps with the target field 713 of the ultrasonic source in a second overlapping area 722. Figure 7In the case shown, the first overlap region is a strict subset of the second overlap region, but this is not necessarily the case - there will be areas where the first overlap region intersects the second overlap region, but the first overlap region may have sub-regions outside the second overlap region and vice versa.

[0038] The "target field" of ultrasound refers to the volume exposed to ultrasound in the absence of any reflecting surfaces other than the reflecting surface of the ultrasound distance sensor itself, i.e., equivalent to Figure 3 The illumination field of the light source in .

[0039] An object 704 having a surface within the two overlapping regions will generate a signal R at the first sensor. 1 , and generates a signal R at the second sensor 2 . R 1 and R 2 Each of these will depend primarily on the area of ​​the surface in each region, the reflectivity of the surface, and the intensity of the ultrasound source. 1 / R 2 (and its inverse) will not depend on the reflectivity or other surface properties of the surface (assuming it is uniform, which is a good approximation for small areas in most cases), as this will cancel out. Therefore, this ratio (or its inverse) can be used (with suitable calibration) to determine the distance between the optical sensor and the surface.

[0040] All of the specific examples described above for optical sensors also apply to ultrasonic sensors, e.g., the sensor's field of view and field of view can be any suitable shape or alignment, and multiple ultrasonic sources can be used. Similar to optical sensors, ultrasonic sensors can be combined with ultrasonic time-of-flight sensors, where the distance threshold determines which sensor is used to provide the final reading.

[0041] List of reference numerals:

[0042] 101 Light Source

[0043] 102 Light Sensor

[0044] 103 objects

[0045] 111 Light source 101 lighting field

[0046] 112 Field of view of light sensor 102

[0047] 113 Overlapping area between 111 and 112

[0048] 114 Path of reflected light

[0049] 201 Light Sensor

[0050] 202 Light Source

[0051] 203 Light Source

[0052] 211 Field of view of light sensor 201

[0053] 212 Light source 202 lighting field

[0054] 213 Light source 203 lighting field

[0055] 221 is the overlapping area between 211 and 212

[0056] 222 Overlapping area between 221 and 213

[0057] 301 Light Sensor

[0058] 302 light sensor

[0059] 303 light source

[0060] 304 Object

[0061] 311 Field of view of light sensor 301

[0062] 312 Field of view of light sensor 302

[0063] 313 Light source 303 lighting field

[0064] 321 overlaps the area between 311 and 313

[0065] 322 Overlapping area between 312 and 313

[0066] 401 Light Sensor

[0067] 402 Light Sensor

[0068] 403 light source

[0069] 404 Object

[0070] 411 Field of view of light sensor 401

[0071] 412 Field of view of light sensor 402

[0072] 413 Light source 403 lighting field

[0073] 421 is the overlapping area between 411 and 413

[0074] 422 is the overlapping area between 412 and 413

[0075] 501 Time of Flight Sensor

[0076] 502 optical distance sensor

[0077] 601 light source

[0078] 602 Light Sensor

[0079] 603 Light Sensor

[0080] 611 Time of Flight Sensor

[0081] 612 Optical Distance Sensor

[0082] 613 Controller

[0083] 701 Ultrasonic Sensor

[0084] 702 Ultrasonic Sensor

[0085] 703 Ultrasonic Source

[0086] 704 Object

[0087] 711 Field of view of ultrasonic sensor 701

[0088] 712 Field of view of ultrasonic sensor 702

[0089] 713 Illumination field of ultrasound source 703

[0090] 721 is the overlapping area between 711 and 713

[0091] 722 Overlapping area between 712 and 713

Claims

1. An optical sensor, comprising: a light source (303) having an illumination field (313); A first light sensor (301) and a second light sensor (302) having respective first fields of view (311) and second fields of view (312); in: The intersection of the illumination field and the first field of view forms a first overlapping region (321); The intersection of the illumination field and the second field of view forms a second overlapping region (322); such that when a surface (304) is within one or both of the first overlap region and the second overlap region, the surface reflects light from the light source to a corresponding light sensor; A controller is configured to determine a first distance measurement to a surface within one or both of the first overlap region and the second overlap region based on a ratio of reflected light from the light source received by the first light sensor to reflected light from the light source received by the second light sensor. 2 . The optical sensor of claim 1 , wherein the first overlap region is a subset of the second overlap region, or the second overlap region is a subset of the first overlap region. 3 . The optical sensor according to claim 1 , wherein the first overlap region has a sub-region outside the second overlap region, and the second overlap region has a sub-region outside the first overlap region.

4. The optical sensor according to any one of claims 1 to 3, wherein the controller is further configured to: applying modulation to the light source; determining a second distance measurement to the surface based on a time of flight of reflected light from the light source to the first sensor; If at least one of the first distance measurement or the second distance measurement is below a threshold distance, the first distance measurement is output, and if at least one of the first distance measurement or the second distance measurement is above a threshold distance, the second distance measurement is output. The optical sensor of claim 4 , wherein the threshold distance is between 50 mm and 100 mm.

6. An optical sensor array, comprising: An optical sensor (502) according to any one of claims 1 to 3; an optical time-of-flight sensor (501) comprising a third light sensor, a further light source, and a time-of-flight system configured to determine a second distance measurement to the surface based on a time of flight of light emitted by the further light source, reflected by an object, and received by the third light sensor; Wherein the controller is configured to output the first distance measurement if at least one of the first distance measurement or the second distance measurement is below a threshold distance, and to output the second distance measurement if at least one of the first distance measurement or the second distance measurement is above a threshold distance.

7. The optical sensor array of claim 6, wherein the threshold distance is between 50 mm and 100 mm.

8. A method of operating an optical sensor, the optical sensor comprising: a light source having an illumination field; a first light sensor and a second light sensor having respective first and second fields of view; in: The intersection of the illumination field and the first field of view forms a first overlapping region; The intersection of the illumination field and the second field of view forms a second overlapping region; so that when the surface is within the first overlapping region and / or the second overlapping region, the surface reflects light from the light source to the corresponding light sensor; The method includes determining a distance to a surface within one or both of the first overlap region and the second overlap region based on a ratio of reflected light from the light source received by the first light sensor to reflected light from the light source received by the second light sensor.

9. An ultrasonic sensor, comprising: an ultrasound source (703) having a target field (713), the target field being a volume exposed to ultrasound from the source; A first ultrasonic sensor (701) and a second ultrasonic sensor (702) having respective first fields of view (711) and second fields of view (712); in: The intersection of the target field and the first field of view forms a first overlapping area (721); The intersection of the object field and the second field of view forms a second overlapping region (722); so that when a surface (704) is within one or both of the first overlapping region and the second overlapping region, the surface reflects ultrasound from the ultrasound source to a corresponding ultrasound sensor; a controller configured to determine a first distance measurement to the surface within one or both of the first overlapping region and the second overlapping region based on a ratio of the reflected ultrasound from the ultrasound source received by the first ultrasound sensor to the reflected ultrasound from the ultrasound source received by the second ultrasound sensor. 10 . The ultrasonic sensor of claim 9 , wherein the first overlap area is a subset of the second overlap area, or the second overlap area is a subset of the first overlap area. 11 . The ultrasonic sensor according to claim 9 , wherein the first overlapping region has a subregion outside the second overlapping region, and the second overlapping region has a subregion outside the first overlapping region.

12. A method of operating an ultrasonic sensor, the ultrasonic sensor comprising: an ultrasound source having a target field, the target field being a volume exposed to ultrasound from the source; a first ultrasonic sensor and a second ultrasonic sensor having respective first and second fields of view; in: The intersection of the object field and the first field of view forms a first overlapping area; The intersection of the object field and the second field of view forms a second overlapping area; so that when the surface is within the first overlapping region and / or the second overlapping region, the surface reflects ultrasound from the ultrasound source to the corresponding ultrasound sensor; The method includes determining a distance to a surface within one or both of the first overlap region and the second overlap region based on a ratio of reflected ultrasound from the ultrasound source received by the first ultrasound sensor to reflected ultrasound from the ultrasound source received by the second ultrasound sensor.

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