Wet floor detection using an infrared time of flight sensor

Abstract

Detecting a presence of a liquid on a reflective surface using a ToF sensor system, wherein one or more infrared (IR) emitters (130-134) emit IR light via the reflective surface to a ToF sensor (110), wherein the ToF sensor receives the IR light, wherein the ToF sensor system determines a change in intensity of the received IR light, and wherein the ToF sensor system determines the presence of the liquid on the reflective surface based on the change in intensity of the received IR light.

Description

[0001] WET FLOOR DETECTION USING AN INFRARED TIME OF FLIGHT SENSOR

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a Time-of-Flight (ToF) sensor system. More specifically, the present disclosure relates to a ToF sensor system for detecting a presence of liquid on a surface, a light fixture including a ToF sensor for use in such system, and a method of detecting a presence of a liquid on a surface.

[0004] BACKGROUND

[0005] Water on a floor can potentially be dangerous. It may cause slip and fall accidents since water creates a slippery surface, increasing the chances of slip and fall. This is especially true if the flooring material is already slippery. It may also cause electrical hazards. If the water encounters electrical outlets, appliances, or wires, it can pose a serious risk of electric shock. To ensure safety, it can be important to detect and address water on the floor promptly, e.g., by cleaning up the water and drying the area thoroughly to prevent accidents and minimize the risk of damage.

[0006] US2021156993A1 discloses a robotic cleaning appliance including a housing, surface treatment item, surface type detection sensor, and processor. The sensor emits sonic signals toward a surface being traversed and receives corresponding returned signals from the surface and a reflectivity metric is determined and compared to a stored value; and based on the comparison, determines a type of the surface.

[0007] EP3514579A1 relates to a road surface condition prediction system. Moisture information obtainer includes near-infrared light source, light detector, radiation temperature measurer, and discriminator. Based on the intensity of scatter-reflected light of the infrared light by the road surface, moisture information obtainer detects the moisture on the road surface as a spot type.

[0008] JP2016223795A relates to a distance image acquisition part acquires a first distance image and a second distance image. The first distance image uses a light with such a wavelength that makes the light reflect from a liquid and a floor surface. The second distance image uses a light with such a wavelength that makes the light transmit through a liquid and reflect from a floor surface. Then, a difference extraction part extracts the difference between the first and second distance images. A liquid detection unit thereafter conducts matching with the difference, using shape data on a large number of liquids stored in a storage part, and presumably determines that a liquid exists on the floor surface if the value with the largest correlation of the correlations between the shape data on the difference and the shape data on the various different types of liquids is not smaller than a predetermined threshold value.

[0009] SUMMARY

[0010] A summary of aspects of certain examples disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects and / or a combination of aspects that may not be set forth.

[0011] The present disclosure aims to overcome the drawbacks identified in the background section. In particular, the present disclosure aims to detect liquids, such as water, on a surface, such as a floor. Detected liquids may indicate a leakage and / or result in dangerous situations, such as described in the background section, which may be resolved after detection of the liquid.

[0012] According to an aspect of the present disclosure, a ToF sensor system is presented. The ToF sensor system may include a ToF sensor arranged to receive infrared (IR) light. The ToF sensor system may further include one or more IR emitters arranged to emit IR light via a reflective surface to the ToF sensor. The ToF sensor system may further include one or more processors. The one or more processors may be arranged to determine a change in intensity of the received IR light. The one or more processors may further be arranged to determine a presence of a liquid on the reflective surface based on the change in intensity of the received IR light.

[0013] One or more of such processors may be part of the ToF sensor and / or part of a data processing part that is communicatively connected to the ToF sensor.

[0014] In an embodiment, the one or more processors may be arranged to determine the change in intensity of the received IR light for each of the IR emitters individually.

[0015] In an embodiment, the ToF sensor system may include a plurality of IR emitters arranged to emit IR light via the reflective surface to the ToF sensor under different angles of inclination from each of the IR emitters to the reflective surface.

[0016] In an embodiment, the one or more processors may be arranged to determine an intensity of background IR light by measuring IR light at the ToF sensor without the one or more IR emitters emitting IR light. The one or more processors may further be arranged to subtract the intensity of the background IR light from the intensity of the received IR light originating from the one or more IR emitters before determining the change in intensity of the received IR light.

[0017] In an embodiment, at least one of the one or more IR emitters may be arranged to emit a low-frequency and low duty cycle periodic IR square wave light. The ToF sensor may be arranged to continuously monitor a change in the intensity of the background IR light. The one or more processors may be arranged to detect a periodicity based on the change in the intensity of the background IR light to determine a timing for emitting the IR light for the at least one of the one or more IR emitter.

[0018] In an embodiment, the one or more processors may be arranged to determine a change in distance between each IR emitter and the ToF sensor. The one or more processors may further be arranged to, based on the change in distance, determine one or more of: the presence of the liquid on the reflective surface; a thickness of the liquid on the reflective surface; a presence of an item other than the liquid on the reflective surface.

[0019] In an embodiment, the one or more processors may be arranged to calculate a normalized change in the intensity of the received IR light. The one or more processors may further be arranged to calculate a normalized change in the distance. The one or more processors may further be arranged to determine the presence of the liquid on the reflective surface based on the normalized change in the intensity of the received IR light exceeding a first threshold value and the normalized change in the distance exceeding a second threshold value.

[0020] In an embodiment, the ToF sensor may be a multipixel ToF sensor. Each pixel of the multipixel ToF sensor may cover a different portion of the reflective surface.

[0021] In an embodiment, the one or more processors may be arranged to determine the presence of the liquid when the change in intensity of the received IR light is determined for a plurality of adjacent pixels.

[0022] In an embodiment, the ToF sensor may include one of the one or more IR emitters.

[0023] In an embodiment, the ToF sensor system may include one IR emitter. The IR emitter may be a part of the ToF sensor.

[0024] In an embodiment, the ToF sensor system may further include a lighting fixture. The ToF sensor may be a part of the lighting fixture. According to an aspect of the present disclosure, a lighting fixture for use in a ToF sensor system is presented. The ToF sensor system may have one or more of the abovedescribed features and may be used for determining a presence of a liquid on a reflective surface based on a change in intensity of IR light. The lighting fixture may include a light source. The lighting fixture may further include a ToF sensor arranged to receive the IR light from one or more IR emitters via the reflective surface.

[0025] According to an aspect of the present disclosure, a method of detecting a presence of a liquid on a reflective surface is presented. The method may include emitting, by one or more IR emitters, of IR light via the reflective surface to a ToF sensor. The method may further include receiving, by the ToF sensor, of the IR light. The method may further include determining a change in intensity of the received IR light. The method may further include determining the presence of the liquid on the reflective surface based on the change in intensity of the received IR light.

[0026] In an embodiment, The method may further include determining a change in distance between each IR emitter and the ToF sensor. The method may further include, based on the change in distance, determining one or more of: the presence of the liquid on the reflective surface; a thickness of the liquid on the reflective surface; a presence of an item other than the liquid on the reflective surface.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbol indicate corresponding parts, in which:

[0029] Fig. 1 shows an abstract representation of a ToF sensor system arranged in a room, according to an aspect of the present disclosure;

[0030] Figs. 2a-d represent detected IR reflections in time for different IR emitters;

[0031] Figs. 3a-d represent detected IR reflections in time for different types of surfaces;

[0032] Fig. 4 represents an example multipixel sensor area of a ToF sensor;

[0033] Fig. 5 shows an abstract representation of a lighting fixture including a ToF sensor, according to an aspect of the present disclosure;

[0034] Fig. 6 shows an example embodiment of a computing system for implementing certain aspects of the present technology; and Fig. 7 shows steps of a method of detecting a liquid using a ToF sensor, according to an aspect of the present disclosure.

[0035] The figures are intended for illustrative purposes only, and do not serve as restriction of the scope of the protection as laid down by the claims.

[0036] DETAILED DESCRIPTION

[0037] It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0038] The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the present disclosure is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[0039] Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present disclosure should be or are in any single example of the present disclosure. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same example.

[0040] Furthermore, the described features, advantages, and characteristics of the present disclosure may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the present disclosure. Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present disclosure. Thus, the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0041] Contact sensors are known to detect water on floor. Such contact sensors may face certain inconveniences since they typically have a specific point of contact with water being detected. This limitation makes it challenging to detect water across larger areas.

[0042] Contact-less sensors are known that can detect water on a surface, such as a surface of a road. Such contact-less sensors typically use multiple infra-red (IR) emitters to emit IR lights with different wavelengths and then measure the IR lights reflected by the surface. The absorption of IR light by water depends on the wavelength of the IR light. By monitoring the variations of the reflected IR lights of different wavelengths, the sensor can determine if there is water on the surface or not. These sensors are usually big and expensive.

[0043] The present disclosure presents a method to detect a liquid, such as water, on an object, particularly on a surface of such object, e.g., a floor. Advantageously, only one IR ToF sensor may be used, although multiple ToF sensors are possible. One or more IR emitters are located in the neighboring space of the ToF sensor. The one or more IR emitters emit IR light and reflected IR light may be detected by the ToF sensor from which an amount of reflected IR light may be determined. The solution of the present disclosure does not depend on different wavelengths of IR light.

[0044] The ToF sensor is typically part of a ToF sensor system including data processing capabilities for processing information obtained by the ToF sensor. The ToF sensor system may be implemented as a single device or include multiple communicatively connected parts forming the ToF sensor system. The ToF sensor may be a multipixel IR ToF sensor, e.g., a 64 pixels ToF sensor.

[0045] The ToF sensor system may include the one or more IR emitters. One or more or all of the IR emitters may be implemented separately from the ToF sensor system. An IR emitter may be part of the ToF sensor. The ToF sensor system may include multiple ToF sensors.

[0046] In an example embodiment, the ToF sensor and IR emitters may be components of a connected lighting system. For example, the ToF sensor may be integrated by a lighting fixture. The IR emitter may be a part of a security camera, a Li-Fi transmitter, or any other device including a suitable IR emitter, possibly another ToF sensor or lighting fixture. In an example embodiment, there may be a floor area in the Field of View (FoV) of a ToF sensor and one or more IR emitters may emit IR light on the floor area. In this example embodiment, the ToF sensor may include an IR emitter. The ToF sensor (i.e., its IR emitter) and the one or more other IR emitters may emit IR lights toward the floor area one by one. With the ToF sensor and IR emitters located at different locations, the IR lights from the IR emitters may hit the floor surface at different angles of incidence. After reflecting off the floor, the reflected IR lights may be received by the ToF sensor (e.g., its IR receiver), possibly via one or more further reflections from one or more other surfaces, such as a wall. The amount of reflected IR lights of each of the IR emitters may depend on the angle of incidence of the incident IR lights. If there is a liquid, in this example water, on the floor, the amount of reflected IR lights from the IR emitters may be decreased as compared to when the floor is dry. Knowing the amount of reflected IR lights from the IR emitters (i.e., different angles of incidence) when the floor is dry and comparing this data with the currently detected amount of reflected IR lights, the ToF sensor system may determine that the floor is wet (e.g., covered by a film of water) if the amount of reflected IR light from one or more of the IR emitters is decreased.

[0047] Optionally, before reporting a detection of a wet surface, such as a floor, the ToF sensor system, through the ToF sensor, may further determine a measured distance to the surface area to avoid any false positive. For example, if the measured distance remains the same or increases just slightly due to the thickness of water on a floor as compared to when the floor is dry, the ToF sensor system may report the detection of the wet floor.

[0048] Optionally, the presence of a liquid, such as water, may be detected on a surface, such as a floor, by a multipixel ToF sensor by determining there are both decreased reflected IR light and (slightly) increased measured distance (e.g., due to the thickness of the liquid on the surface) in an area that covers several continuous detection pixels of the ToF sensor.

[0049] The ToF sensor of the present disclosure may be configured to measure the intensity of received IR light. When an IR emitter, such as an emitter of the ToF sensor itself or a sperate IR emitter, emits IR lights that hits and reflects off an object in the FoV of the ToF sensor, the intensity of the reflected IR light which is received by the ToF sensor may be measured.

[0050] The amount of reflected IR light, which may be a portion of the IR light hitting the object, is typically determined by the characteristics (e.g., material, color, etc.) of the surface of the object, the incident angle of the IR light, and the exit angle of the reflected light.

[0051] Where in the following examples water is detected on a floor, it will be understood that the present disclosure is not limited to water and floors and that other liquids may be detected and other surfaces may be targeted by the ToF sensor system.

[0052] Fig. 1 shows an abstract representation of an example embodiment of a ToF sensor system 100. In the example of Fig. 1, the ToF sensor system 100 includes a ToF sensor 110 that may be installed on the ceiling 102 of a room. Alternatively, the ToF sensor 110 may be installed at a different location in the room, e.g., on a wall 104. The ToF sensor may include an IR receiver 120. The ToF sensor system 100 may further include one or more IR emitters, in this example a first IR emitter 130 as a part of the ToF sensor 110, a second IR emitter 132 located on the ceiling 102 and a third IR emitter 134 located on a wall 104. IR light emitted from each of the IR emitters 130-134 may be reflected by a floor 106 of the room and detected by the IR receiver 120, as depicted by the dashed arrows.

[0053] The ToF sensor system 100 may further include one or more processors for processing information obtained by the ToF sensor 110. In an example embodiment, one or more processors 112 may be part of the ToF sensor 110. In an example embodiment, the ToF sensor system 100 may include a data processing part 140 including one or more processors 142. In the example of Fig. 1, the data processing part 140 may be communicatively connected to the ToF sensor 110 via a data network 150. In an example embodiment, information obtained by the ToF sensor 110 may be processed by processor 112 of the ToF sensor 110 and further processed by the processor 142 of the data processing part 140.

[0054] With reference to the examples of Fig. 2, the ToF sensor 120 may continuously measure the intensity of received IR light. Fig. 2a represents a side view of a room at time tl. At tl, no IR light is emitted by any active IR emitters and arrow 12 represents a received ambient IR light Rx_l in the environment as measured by the ToF sensor 120. Fig. 2b represents a side view of the room at time t2, where an IR emitter of the ToF sensor 120 itself emits IR light Tx ToF represented by arrow 20. Arrow 22 represents a received IR light Rx_2 of the emitted IR light 20 after reflecting by a floor area 2 and received by the ToF sensor 120. Fig. 2c represents a side view of the room at time t3, where a separate IR emitter 132 emits IR light Tx IR emitter represented by arrow 30. Arrow 32 represents a received IR light Rx_3 of the emitted IR light 30 after reflecting by the same floor area 2 and received by the ToF sensor 120. Fig. 2d shows a graph with the intensity of IR light (y-axis) as received by one pixel of the ToF sensor 120 in time (x-axis), in this example at time tl, t2 and t3 of Figs. 2a- c. The intensity may be measured in kilo-counts per second, which indicates the quantity of photons received by the ToF sensor 120. Along the y-axis the intensities as a result of reflections 12, 22 and 32 are indicated.

[0055] In an example embodiment, each IR emitter 130-134 may emit a low- frequency and low duty cycle periodic IR square wave light. The ToF sensor 120 may continuously monitor a change in ambient IR light 12 and detect the periodicity to determine a timing of the IR emitter 130-134.

[0056] By subtracting Rx_l 12 from Rx_2 22 and Rx_3 32 respectively, a representation of intensities of received IR lights which are emitted by IR emitters (in Fig. 2, the IR emitter in the ToF sensor 120 and the separate IR emitter 132) and reflected by the same floor area 2 may be determined. Advantageously, the absolute value of the reflectance need not be determined, but changes in reflectance may be used to detect the presence of water on the floor 106.

[0057] The ToF sensor system 100 of the present disclosure may be used to detect liquids on different kinds of surfaces, such as wooden surfaces, ceramic surfaces or any other surface capable of reflecting IR light. Optionally, items that are placed on top of the surface, such as an item of paper material or an item of cloth material, may be distinguished from liquids, which items have different IR reflective properties compared to the surface with a liquid. Moreover, the ToF sensor system 100 of the present disclosure may be used to detect liquids on surfaces having any color.

[0058] A liquid, such as water, absorbs IR light. Therefore, the amount of IR light reflected by a surface, such as a floor, will decrease if there is a liquid on the surface. The degree of decrease may depend on the angle of incidence and the exit angle of the IR light.

[0059] In an example embodiment, the position of the ToF sensor 120 and the surface area, e.g., floor area 2, may be fixed. As a result, all the IR lights (e.g., 22, 32) that are reflected by the floor area 2 and received by the ToF sensor 120 may have the same exit angle, e.g., 20°. By changing the position of the separate IR emitters (e.g., 132, 134), IR lights (e.g., 30) hitting the floor area 2 with different angles of incidence may be created, e.g., 15°, 30° and 40°. In this example, the IR light 20 from the ToF sensor 120 may hit the floor area 2 with a -20° angle of incidence. It will be understood that different positions of the ToF sensor and / or IR emitters may result in different angles of incidence. Fig. 3 shows four graphs (Figs. 3a-3d) with example values of relative reflectance comparing dry and wet surfaces for different types of surfaces and comparing the dry surfaces with surfaces including an item placed on top of the surface. The graphs have been produced using test results in a test environment. In these examples, the liquid being detected is water. Along the x-axes the light incident angle in degrees is plotted, with different light incident angles corresponding to IR light emitted by different IR emitters, such as 130-134. Along the y-axes the IR reflectance change, i.e., based on the detected IR intensity at an IR receiver 120 of a ToF sensor 110, is plotted.

[0060] Fig. 3a shows the relative reflectance of a wood floor, with line 302 corresponding to a dry wood floor and line 304 corresponding to the wood floor with water. Fig. 3b shows the relative reflectance of the wood floor, with line 312 corresponding to the dry wood floor, line 314 corresponding to a white piece of paper on the wood floor, line 316 corresponding to a black piece of cloth on the wood floor and line 318 corresponding to a white piece of cloth on the wood floor. Fig. 3c shows the relative reflectance of a ceramic floor, with line 322 corresponding to a dry ceramic floor and line 324 corresponding to the ceramic floor with water. Fig. 3d shows the relative reflectance of the ceramic floor, with line 332 corresponding to a white piece of paper on the ceramic floor, line 334 corresponding to a black piece of cloth on the ceramic floor, line 336 corresponding to the dry ceramic floor and line 338 corresponding to a white piece of cloth on the ceramic floor.

[0061] Test results are obtained for four angles of incidence: -20°, 15°, 30° and 40°. In Fig. 3a, the intensities of the dry wood floor 302 are normalized as 1 (100%) and the intensities of the wood floor with water 304 are presented as a percentage of the corresponding intensity of the dry wood floor 302. In the same manner, in Fig. 3b the result of the wood floor 312 and the three different non-water objects (white paper 314, black cloth 316, white cloth 318) on the wood floor are presented. Figs. 3c and 3d show the same results, but for a ceramic floor. The result shows that water on both wood floor and ceramic floor decrease the intensities of all different angles of incidence, while non-water objects on the floor can cause either increases or decreases of intensities for different angles of incidence. This way, water on the floor may be detected and distinguished from other, non-wet items on the floor.

[0062] The ToF sensor 110 is typically a depth sensor. It’s IR emitter 130 and / or other IR emitters 132, 134 may emit a burst of IR light, which travels through the air, reflects off an object such as the floor 106, and returns to the ToF sensor 110, where it may be detected by the IR receiver 120. By counting the time between the emitting of IR light and receiving of the reflected IR light, the distance between the ToF sensor 110 and the object may be obtained.

[0063] The speed of light in water is slower than its speed in air. The exact speed depends on the properties of the water, such as temperature and density. As a general approximation, the speed of light in water is about 225,000 kilometers per second, which is roughly 75% of the speed of light in air. Other liquids may have different properties, but generally the speed of light will be different in and out of the liquid.

[0064] When there is a water film on the floor 106, the IR light may take a little longer time to travel back to the ToF sensor 110, which causes an increase in distance measurements. Note that this measured change in distance is a perceived distance chance due to the change in the speed of light in the water (or more generally in the liquid on the reflective surface). The actual distance may be different from the measured distance. The measured distance increasement value depends on the thickness of the water film. On the other side, when there is a non-IR-transmitting object such as wiping cloth on the floor, the light may return to the ToF sensor in a slightly shorter time, which causes a decrease in distance measurements. Table 1 below shows example distance values measured when there is water on the floor 106, by a ToF sensor 110 under different heights. The results show that when there’s water on floor, the distance measurements will slightly increase. This can be used to confirm there is water on the floor.

[0065] Table 1

[0066] The shape of water on the floor 106 usually has certain shapes, such as ellipses and circles or shapes similar to these. Moreover, the area covered with water typically gradually becomes larger over time. Fig. 4 shows an example multipixel (in this example 64 pixels) sensor area 400 of a ToF sensor, such as ToF sensor 110. Each pixel P1-P64 of the ToF sensor 110 corresponds to an area on the floor 106 covered by each of the pixels. In Fig. 4, the shape of an initial water area 402 (dark area) and the change of shape over time, shown as later water area 404 (dashed area) are projected onto the multipixel sensor area 400 and may be detected by the ToF sensor 110. By checking the overall shape and temporal variation of possible water areas, the determination of the floor being wet may be improved.

[0067] In the following example embodiment, the ToF sensor system 100 includes one multipixel (e.g., 64 pixels) IR ToF sensor 110 including an IR emitter 130 and an IR receiver 120. No further IR emitters are required in this example embodiment. The ToF sensor 110 may be used to detect the presence of a liquid on a surface, in this example water on a floor 106. When there is a water film on the floor 106, water absorbs IR light, therefore the amount of IR light (e.g., intensity) reflected by the floor 106 will decrease. At the same time, the light of the IR emitter 130 of the ToF sensor 110 will take a little longer time to travel back, which causes an increase in distance measurements. When both decreased reflected IR light and slightly increased measured distance in an area are detected, it may be concluded that this area is probably covered by water.

[0068] Optionally, to get reliable detection results, it may be concluded that water is detected when a change in intensity and / or distance is detected in an area that covers multiple adjacent detection pixels of the ToF sensor 110, such as the pixels P25, P26, P27, P33, P34, P35, P36, P41, P42, P43, P44, P49, P50, P51, P52, P57, P58 and P59 in Fig. 4, where initial water area 402 may be detected.

[0069] To remove potential random fluctuations in the measured IR signal and distance values of the ToF sensor, multiple measurements over a period of time may be taken and averaged. Following tables 2.1-2.3 show examples of averaged distance and IR reflectance data for 64 pixels of an example 64 multipixel IR ToF sensor. Data from multiple measurements may be averaged, with one measurement resulting in one frame of data with measurement values for each of the pixels at one moment in time. The layout of the pixels in the tables 2.1-2.3 is similar to P1-P64 shown in Fig. 4.

[0070] Table 2.1 shows the measurement data of a floor without any water, averaged over 100 frames. Table 2.2 shows the measurement data of the floor with some water, averaged over 100 frames. Table 2.3 shows the distance and IR reflectance change between these two situations, i.e., a delta between tables 2.2 and 2.1. In table 2.3, the adjacent connected highlighted pixels are pixels with both a slight distance increase and an IR reflectance decrease above predefined threshold values, from which it may be determined that water is present on the floor in this area. The predefined threshold values may be different for different types of liquids and different types of surfaces. In the example of table 2.3, the predefined threshold value for the normalized distance chance may be set to +1.0mm and the predefined threshold value for the normalized IR reflectance change may be set to -3.0%. Thus, in the example of table 2.3, for pixels having a normalized distance change of 1.0mm or larger and at the same time having a normalized IR reflectance change of -3.0% or lower, it may be determined that the floor is wet.

[0071] Distance (mm) IR Reflectance

[0072] Table 2. 1: Distance and IR reflectance of floor without water (averaged value of lOOframes)

[0073] Distance (mm) IR Reflectance

[0074] Table 2. 2: Distance and IR reflectance of floor with some water

[0075] (averaged value of lOOframes) Normalized Distance change (mm) Normalized IR Reflectance change (%)

[0076] Table 2.3: Distance and IR reflectance change

[0077] Different kinds of liquid may be detected on a surface using the solution of the present disclosure. Non limiting examples of such liquids are water, detergent, yellow beverage, milk and coffee. Milk and coffee are opaque, but since its liquid film is not thick, it is still translucent in some extent. In general, opaque liquids may be detected when its liquid film is thin enough to allow the surface area under the liquid to reflect IR light.

[0078] Following tables 3.1-3.4 show examples of normalized distance change data and normalized IR reflectance change data for 64 pixels of an example 64 multipixel IR ToF sensor for different kinds of liquid. The normalized data has been obtained similarly to table 2.3. The layout of the pixels in the tables 3.1-3.4 is similar to P1-P64 shown in Fig. 4. Table 3.1 shows data of detecting detergent, with the highlighted pixels indicating where it is determined that detergent is present. Table 3.2 shows data of detecting a yellow beverage, with the highlighted pixels indicating where it is determined that yellow beverage is present. Table 3.3 shows data of detecting milk, with the highlighted pixels indicating where it is determined that milk is present. Table 3.4 shows data of detecting coffee, with the highlighted pixels indicating where it is determined that coffee is present.

[0079] Normalized Distance change (mm) Normalized IR Reflectance change (%)

[0080] Table 3.1 Distance and IR reflectance change (Detergent)

[0081] Normalized Distance change (mm) Normalized IR Reflectance change (%)

[0082] Table 3.2 Distance and IR reflectance change (Yellow beverage)

[0083] Normalized Distance change (mm) Normalized IR Reflectance change (%) Table 3.3 Distance and IR reflectance change (Milk) Normalized Distance change (mm) Normalized IR Reflectance change (%)

[0084] Table 3.4 Distance and IR reflectance change (Coffee)

[0085] In an example embodiment, the ToF sensor of the present disclosure may be implemented in a lighting fixture. Fig. 5 shows an abstract representation of a lighting fixture 500 including a ToF sensor 502 according to the present disclosure and a light source 504. An example of the ToF sensor 502 is the ToF sensor 110 of Fig .1. The lighting fixture 500 and / or the light source 504 may be controllable via a data network. In an embodiment, the data network of the lighting fixture 500 and / or light source 504 may be separate from a data network of the ToF sensor 502. In another embodiment, the data network of the lighting fixture 500 and / or light source 504 may be the same as the data network of the ToF sensor 502. Multiple lighting fixtures 500 may form an integrated, connected network of lighting fixtures. An example of the data network of the ToF sensor 502 is data network 150 used for the ToF sensor system 100.

[0086] In an example embodiment, the ToF sensor system 100 may be part of an elderly care system. Preferably, such elderly care system includes one or more lighting fixtures 500 with integrated ToF sensor 502.

[0087] Fig. 6 shows an example embodiment of a computing system 600 for implementing certain aspects of the present technology. In various examples, the computing system 600 may be any computing device making up the ToF sensor 110, the IR emitter 132- 134, the data processing part 140, the ToF sensor system 100, or any other computing system described herein.

[0088] In some implementations, a computing system 600 may implement the methods described herein, such as method 700 of the present disclosure.

[0089] The computing system 600 may include any component of a computing system described herein, which components may be in communication with each other using connection 605. The connection 605 may be a physical connection via a bus, or a direct connection into processor 610, such as in a chipset architecture. The connection 605 may also be a virtual connection, networked connection, or logical connection.

[0090] In some implementations, the computing system 600 may be a distributed system in which the functions described in this disclosure may be distributed within a datacenter, multiple datacenters, a peer network, etc. In some embodiments, one or more of the described system components represents many such components each performing some or all of the functions for which the component is described. In some embodiments, the components may be physical or virtual devices.

[0091] The example system 600 includes at least one processing unit (CPU or processor) 610 and a connection 605 that couples various system components including system memory 615, such as read-only memory (ROM) 620 and random-access memory (RAM) 625 to processor 610. The computing system 600 may include a cache of high-speed memory 612 connected directly with, in close proximity to, or integrated as part of the processor 610.

[0092] The processor 610 may include any general -purpose processor and a hardware service or software service, such as services 632, 634, and 636 stored in storage device 630, configured to control the processor 610 as well as a special -purpose processor where software instructions are incorporated into the actual processor design. The processor 610 may essentially be a completely self-contained computing system, containing multiple cores or processors, a bus, memory controller, cache, etc. A multi-core processor may be symmetric or asymmetric.

[0093] To enable user interaction, the computing system 600 may include an input device 645, which may represent any number of input mechanisms, such as a microphone for speech, a touch-sensitive screen for gesture or graphical input, keyboard, mouse, motion input, speech, etc. The computing system 600 may also include an output device 635, which may be one or more of a number of output mechanisms known to those of skill in the art. In some instances, multimodal systems may enable a user to provide multiple types of input / output to communicate with the computing system 600. The computing system 600 may include a communications interface 640, which may generally govern and manage the user input and system output. There is no restriction on operating on any particular hardware arrangement, and therefore the basic features here may easily be substituted for improved hardware or firmware arrangements as they are developed. Input device 645 and output device 635 may be sensor related devices. Input device 645 may include an IR receiver, such as IR receiver 120. Output device 635 may include an IR emitter, such as IR emitter 130-134.

[0094] A storage device 630 may be a non-volatile memory device and may be a hard disk or other types of computer readable media which may store data that are accessible by a computer, such as magnetic cassettes, flash memory cards, solid state memory devices, digital versatile disks, cartridges, random access memories (RAMs), read-only memory (ROM), and / or some combination of these devices.

[0095] The storage device 630 may include software services, servers, services, etc., that, when the code that defines such software is executed by the processor 610, causes the system to perform a function. In some embodiments, a hardware service that performs a particular function may include a software component stored in a computer-readable medium in connection with the necessary hardware components, such as processor 610, connection 605, output device 635, etc., to carry out the function.

[0096] Fig. 7 shows an example embodiment of a method 700 of detecting a presence of a liquid on a reflective surface. In step 702, one or more IR emitters 130-134 may emit IR light via the reflective surface to a ToF sensor 110. In step 704, the ToF sensor 110 may receive the IR light. In step 706, a change in intensity of the received IR light may be determined. In step 708, the presence of the liquid on the reflective surface may be determined based on the change in intensity of the received IR light.

[0097] In an example embodiment, in step 710 a change in distance between each IR emitter and the ToF sensor may be determined. Based on the change in distance, in step 708, the presence of the liquid on the reflective surface may be determined, possibly also based on the determined change in intensity of the received IR light. Alternatively or additionally, based on the change in distance, in step 712, a thickness of the liquid on the reflective surface may be determined. Alternatively or additionally, based on the change in distance, in step 714, a presence of an item other than the liquid on the reflective surface may be determined.

[0098] It will be understood that the order of the steps 702-714 may be different to enable the detection of liquid on the reflected surface. For example, steps 706 and 710 may be performed sequentially in any order, at different moments in time in any order or substantially at the same time.

[0099] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. A Time-of-Flight (ToF) sensor system (100) comprising: a ToF sensor (110) arranged to emit infrared (IR) light to a reflective surface and receive infrared (IR) light reflected from the reflective surface, thus to measure the distance between the ToF sensor and the reflective surface; and one or more processors (112, 142) arranged to: determine a change in intensity of the received IR light with reference to an intensity of received IR light when the reflective surface is dry; determine a change in the measured distance between the ToF sensor and the reflective surface with reference to a measured distance between the ToF sensor and the reflective surface when the reflective surface is dry; and determine a presence of a liquid on the reflective surface based on the change in intensity of the received IR light and the change of the measured distance.

2. The ToF sensor system according to claim 1, wherein the ToF sensor system further comprising one or more IR emitters besides an IR emitter embedded in the ToF sensor, the one or more processors are arranged to determine the change in intensity of the received IR light for each of the IR emitters individually.

3. The ToF sensor system according to claim 2, comprising: the IR emitters arranged to emit IR light via the reflective surface to the ToF sensor under different angles of inclination from each of the IR emitters to the reflective surface.

4. The ToF sensor system according to any one of the preceding claims, wherein the one or more processors are arranged to: determine an intensity of background IR light by measuring IR light at the ToF sensor without the one or more IR emitters emitting IR light; andsubtract the intensity of the background IR light from the intensity of the received IR light originating from the one or more IR emitters before determining the change in intensity of the received IR light.

5. The ToF sensor system according to claim 4, wherein at least one of the one or more IR emitters is arranged to emit a low- frequency and low duty cycle periodic IR square wave light; wherein the ToF sensor is arranged to continuously monitor a change in the intensity of the background IR light; and wherein the one or more processors are arranged to detect a periodicity based on the change in the intensity of the background IR light to determine a timing for emitting the IR light for the at least one of the one or more IR emitter.

6. The ToF sensor system according to any one of the preceding claims, wherein the one or more processors are arranged to: based on the change in distance, determine one or more of: a thickness of the liquid on the reflective surface; a presence of an item other than the liquid on the reflective surface.

7. The ToF sensor system according to claim 6, wherein the one or more processors are arranged to: calculate a normalized change in the intensity of the received IR light; calculate a normalized change in the distance; and determine the presence of the liquid on the reflective surface based on the normalized change in the intensity of the received IR light exceeding a first threshold value and the normalized change in the distance exceeding a second threshold value.

8. The ToF sensor system according to any one of the preceding claims, wherein the ToF sensor is a multipixel ToF sensor, and wherein each pixel of the multipixel ToF sensor covers a different portion of the reflective surface.

9. The ToF sensor system according to claim 8, wherein the one or more processors are arranged to:determine the presence of the liquid when the change in intensity of the received IR light is determined for a plurality of adjacent pixels.

10. The ToF sensor system according to any one of the preceding claims, further comprising a lighting fixture (500), and wherein the ToF sensor (502) is a part of the lighting fixture.

11. A lighting fixture (500) for use in a Time-of-Flight (ToF) sensor system according to claim 10 for determining a presence of a liquid on a reflective surface based on a change in intensity of received infrared (IR) light, the lighting fixture comprising: a light source (504); and the ToF sensor (502) arranged to receive the IR light from one or more IR emitters (130-134) via the reflective surface.

12. A method (700) of detecting a presence of a liquid on a reflective surface, the method comprising: emitting (702), by a Time-of-Flight (ToF) sensor (110), of IR light to a reflective surface to the; receiving (704), by the ToF sensor (110), of the IR light reflected by the reflective surface; determining (706) a change in intensity of the received IR light with reference to an intensity of received IR light when the reflective surface is dry; determine a change in the measured distance between the ToF sensor and the reflective surface with reference to a measured distance between the ToF sensor and the reflective surface when the reflective surface is dry; and determining (708) the presence of the liquid on the reflective surface based on the change in intensity of the received IR light and the change of the measured distance.

13. The method according to claim 12, further comprising: based on the change in distance, determining one or more of:- a thickness of the liquid on the reflective surface (712);- a presence of an item other than the liquid on the reflective surface (714).

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