An optical tactile and pressure sensor

Abstract

The invention relates to the field of measuring and testing instruments, more particularly to the field of sensors measuring space-time coordnates of an event to detect the location of the physical contact, as well as pressure applied during the contact. The claimed sensor comprises a light transmitting body, defining a designated interaction surface; a light source; and a light detector. The light source and the detector are located on one the same side of the light transmitting body. The light transmitting body allows the light emitted from the light source to propagate through it due to multiple internal reflections. The light detector collects the emitted light, which is reflected from at least one light transmitting body's surface during the physical contact of an object with the light transmitting body.

Description

[0001] An optical tactile and pressure sensor Field of the invention

[0001] The present invention relates to the field of measuring and testing instruments, more particularly to the field of sensors measuring space-time coordinates of an event, as well as pressure applied. Background of the invention

[0002] An optical tactile and pressure sensors are sensors, which use light to measure the distance from the sensor to location where a surface is under physical contact (e.g., touch) and detect changes in location of physical contact and pressure. This type of sensors works by emitting a pulse of light and measuring the time it takes for the light to travel to a location of physical contact and return back. By analysing the time-of- flight data, the sensor determines the distance from the sensor to location where a surface is under the physical contact and detects changes in pressure. The light of time- of-light sensors travels inside the light transmitting body which has a higher reflective index than the environment (e.g. n_surface=1.3>n_air=1), sufficient optical homogeneity (e.g., no light scattering) and low light absorption (e.g., light extinction coefficient is near zero) to guarantee light transmittance and light guidance even when light transmitting body is positioned on non-planar surfaces.

[0003] Optical time-of-flight based tactile and pressure sensors have several advantages over traditional touch sensors: the material under physical contact (a light transmitting body, where the light emitted from time-of-flight sensor is propagating) is electrode- free surface; they are fast and accurate; and can have any shape to adapt to the environment of application. They can be used in a wide range of applications, such as robotics, medical devices, and automotive systems.

[0004] There are known various types of tactile and pressure sensors. Optical fiber- based sensors, which have been used for pressure and tactile sensing with various designs such as Fabry-Perot interferometers, Bragg gratings, and intensity-based sensors. These sensors have been employed in robotics, prosthetics, and structural health monitoring. Silicon-based photonic sensors: silicon-based photonic sensors, which utilize the interference of light in micro- or nano-scale silicon structures to detect changes in pressure or mechanical deformation. Time of flight Camera-based sensing devices, which have been used in gesture recognition, 3D imaging, and robotics. These cameras rely on measuring the time it takes for emitted light to travel to an object and return to the sensor. By applying this principle to tactile and pressure sensing, it is possible to detect changes in object geometry or pressure distribution. Although not based on optical time of flight technology, capacitive and resistive sensors have been widely used for tactile and pressure sensing. They provide a different approach to sensing and can serve as a point of comparison for optical time of flight- based tactile and pressure sensors.

[0005] There is known a deformable sensor and a method for object localization and force detection using the deformable sensor (US10668627). The known method includes receiving a signal from a deformable sensor comprising data from a deformation region in a deformable membrane resulting from contact with the object utilizing an internal sensor disposed within an enclosure and having a field of view directed through a medium and toward a bottom surface of the deformable membrane. The method also determines a position of the object based on the deformation region of the deformable membrane. The method also determines an amount of force applied between the deformable membrane and the object based on the deformation of the deformable membrane.

[0006] There is known enhanced interaction touch system (US2015 / 346911) based on Frustrated Total Internal Reflection (FTIR), where multiple emitters and detectors can be arranged around the perimeter of a touch surface to form a detection grid, allowing light to propagate through internal reflections and detect touch points across the surface. The system is configured to project light along multiple paths, enabling a touch input mechanism that relies on light diverging and interacting across a distributed grid of detection lines. The main drawback of the known solution is its reliance on multiple emitters and detectors around the entire perimeter, complicating the design and lacking the capability for precise force measurement or interaction timing.

[0007] There is known electronic device having moisture-insensitive optical touch sensors (US11353994), where touch detection is achieved through light transmitted within a cover layer, with the light emitters and detectors located on the same larger surface of the light transmitting body to allow total internal reflection. The system is designed to function effectively in the presence of moisture. The main drawback of the known solution is its relatively limited sensitivity due to the placement of the emitter and detector, which restricts precise force detection and limits the ability to perform accurate temporal analysis of touch interactions. Summary of the invention

[0008] The goal of the invention is to provide an effective touch and pressure sensor based on optical time-of-flight sensor, which is compact, can monitor relatively large areas, and that can be adapted to non-planar contact surfaces with no presence of electrodes on the surface of light transmitting body. The set goal is achieved by providing a touch and pressure sensor based on optical time-of-flight sensor capable to detect physical contact position and pressure. The sensor comprising a light transmitting body, defining a designated interaction surface; the light transmitting body having at least two opposite relatively larger interaction surfaces and multiple smaller edge surfaces between the larger interaction surfaces; a time-of-flight sensor comprising a light source, and a light detector. The light source is designed to emit light pulses with a duration in the sub-nanosecond range. The light source and the detector are located on one and the same smaller edge surface of the light transmitting body. The light transmitting body is designed and situated in a manner that allows the light emitted from the light source to propagate through it laterally at multiple incident angles, reflecting internally across the larger interaction surfaces as the light propagates through the light transmitting body. The light detector is designed to detect the same light signal originally emitted by the light source, reflected from at least one light transmitting body’s interaction surface during the physical contact of an object with the light transmitting body and is subsequently directed back towards the light detector through controlled internal reflection, capturing the time-of-flight measurements of the emitted light signals at multiple incident angles within the light transmitting body. The light transmitting body has a refractive index n in the range from 1 to 3, an extinction coefficient k less than 0.01, and a scattering coefficient less than 0.5 cm-1.

[0009] The set goal is also reached by an optical tactile sensor system comprising a data processing unit; a light transmitting body; one or more sets of the time-of-flight sensors, each comprising a light source, and a light detector. The light source and the detector are located adjacent on one and the same smaller edge of the light transmitting body. The light transmitting body is situated in a manner that allows the light emitted from the light source to propagate through it laterally. The light detector is designed to detect the emitted light signal, which is reflected from at least one light transmitting body’s surface during the physical contact of an object with the light transmitting body and is subsequently directed back towards the light detector through controlled internal reflection within the light transmitting body. The data processing unit configured to receive data from the sensors sets and analyse time interval measurements received from the sensors sets to determine physical contact position by calculating the distance between the sensors set and the point of contact, based on the time it takes for the light to travel from the light source to the point of contact and from the point of contact to light detector. Brief description of drawings

[0010] Fig. 1A – isometric projection of the claimed sensor, showing principle of detecting physical contact position; Fig.1B – side view of the claimed sensor with, showing principle of detecting physical contact position; the angles θc and θe are the angles between the normal of the contact zone with applied force ^⃗^^^ and the emitted and the reflected light beams, respectively θe ≠ 0° and θc ≠ 0°; Fig.2 – top view of the time-of-flight sensor with exclusion zones; Fig.3A – top view of the claimed sensor composed of set of five time-of-flight sensors embedded in the light transmitting body according to another embodiment; Fig. 3B – block diagram, showing embodiment of the claimed system comprising the set of five time-of-flight sensors located as show in Fig.3A; Fig.4A – top view of the claimed sensor composed of set of four time-of-flight sensors in the light transmitting body according to yet another embodiment; Fig. 4B – block diagram, showing embodiment of the claimed system comprising the set of four time-of-flight sensors located as show in Fig.4A; Fig. 5 - a flowchart showing an embodiment of the method for detecting the contact point coordinates with or without the applied force estimation on the light transmitting body using a plurality of the time-of-flight sensors; Fig. 6A - a schematic representation of a robotic arm, which is sensorized with the claimed sensor composed of seven time-of-flight sensors embedded into light transmitting body wrapping the robotic arm; Fig. 6B - a schematic representation of a robotic arm, which is sensorized with the claimed sensor composed of six time-of-flight sensors embedded into light transmitting body wrapping the robotic arm; Fig. 6C - a schematic representation of a robotic arm, which is sensorized with the claimed sensor composed of three time-of-flight sensors embedded into light transmitting body wrapping the robotic arm; Fig. 6D - a schematic representation of a robotic arm, which is sensorized with the claimed sensor composed of ten time-of-flight sensors embedded into light transmitting body wrapping the robotic arm; Fig.7 - a schematic representation of a robotic arm, fully sensorized with the claimed sensor composed of one time-of-flight sensor embedded in the light transmitting body in the form of optical fibre or light guide according to yet another embodiment; Fig. 8 – a schematic proof of concept experiment illustration, showing time of flight sensor with λ = 940 nm and measurements performed in the air; Fig. 9 - a schematic proof of concept experiment illustration, showing time of flight sensor with λ = 940 nm and measurements performed in the water with n = 1.356; Fig.10 – a schematic proof of concept experiment illustration, showing time of flight sensor and an object in the form of a cylinder (dimeter 10 mm, length 20 mm) positioned on the surface of the water in the field of view of the time of flight sensor; Fig.11A - a schematic proof of concept experiment illustration, showing time of flight sensor attached to the light transmitting body made of silicon rubber; Fig.11B – Two-dimensional graph, result of a simulation including a digital twin of a time of flight sensor in the setup illustrated in Fig. 11A, including a data processing stage that translates the times given by the time of flight sensor into a two-dimensional probability map, where darker means higher probability, of a contact point happening on the surface of the light transmitting body; the ground truth contact point (marked as white circumference) is included into the highest probability area of the light transmitting body; Fig.12A - a schematic proof of concept experiment illustration, showing time of flight sensor attached to the light transmitting body made of PMMA in the form of waveguide with 7 mm diameter and 100 mm length. Fig.12B – graph, result of a simulation including a digital twin of a time of flight sensor in the setup illustrated in Fig. 12A, including a possible data processing stage that transforms the times given by the time of flight sensor into the probability of a contact point per distance unit; the ground truth contact point (marked as a vertical line) is detected with higher probability than the rest of the distances. Detailed description of the invention

[0011] The proposed optical touch and pressure sensor 1 is capable to detect physical contact position coordinates and applied pressure during the physical contact.

[0012] The claimed tactile sensor 1 comprises, a light transmitting body 5, defining a designated interaction surface; the light transmitting body 5 having at least two opposite relatively larger interaction surfaces 5` and multiple smaller edge surfaces 5`` between the larger interaction surfaces 5`; a time-of-flight sensor 2 comprising a light source 3, and a light detector 4 (Fig. 1A-1B). The light source 3 can be cavity surface emitting laser – VCSEL, or other light source, and the light detector 4 can be single- photon avalanche diode (SPAD) array, or another light detector. The light source 3 can be designed as a single, dual, or multiple light source arrangement. The light detector 4 can be designed as a single, dual, or multiple light detector arrangement. According to the invention the light source 3 and the detector 4 are located on one the same side of the light transmitting body 5 wherein the light transmitting body 5 is situated in a manner that allows the light emitted from the light source 3 to propagate through it laterally due to the multiple internal reflections. The light detector 4 is designed to detect the emitted light signal, which is reflected from at least one light transmitting body’s 5 surface during the physical contact of an object with the light transmitting body 5 and is subsequently directed back towards the light detector 4 through controlled internal reflection within the light transmitting body 5. The light transmitting body 5 can be mechanically elastic, or mechanically rigid. The sensor 1 can be configured to be placed on planar or non-planar contact surface. Any time of flight sensor’s light source 3 emits light which passes an aperture with diameter Ds(Fig. 2) and has propagation exclusion zone’s one propagation angle φs. The light detector 4 is provided with an exclusion zone two, having an aperture with diameter Ddand exclusion zones’s two prorogation angle φd(Fig.2). As the result, broad field of view is desirable to detected reflected light in the light transmitting body 5 and provide large area touch sensitivity with low number of time of flight sensors 2.

[0013] The light transmitting body 5 has refractive index n in the range from 1 to 3, extinction coefficient k less than 0.01, scattering coefficient less than 0.5 cm-1at the wavelength of the light source 3.

[0014] The claimed invention provides also for an optical tactile sensor 1 system, comprising a data processing unit 9; a light transmitting body 5, defining a designated interaction surface; the light transmitting body 5 having at least two opposite relatively larger interaction surfaces 5` and multiple smaller edge surfaces 5`` between the larger interaction surfaces; one or more sets 20 of the time-of-flight sensors 2, each comprising a light source 3, and a light detector 4. The light source 3 and the detector 4 are located adjacent on one the same smaller edge surface of the light transmitting body 5. The light transmitting body 5 is situated in a manner that allows the light emitted from the light source 3 to propagate through it laterally. The light detector 4 is designed to detect the emitted light signal, which is reflected from at least one light transmitting body’s 5 surface during the physical contact of an object with the light transmitting body 5 and is subsequently directed back towards the light detector 4 through controlled internal reflection within the light transmitting body 5. The data processing unit 9 configured to receive data from the sensors 2 sets 20 and analyse time interval measurements received from the sensors 2 sets 20 to determine physical contact position by calculating the distance between the sensors 2 set 20 and the point of contact, based on the time it takes for the light to travel from the light source 3 to the point of contact and from the point of contact to light detector 4.

[0015] According to an embodiment the light detector 4 can be designed as multiple light detector array (e.g., SPADs) to be capable to detect single photons, where each light detector in the array is configured to detect photons that have been reflected from different points of the light transmitting body’s 5 surface during the physical contact of an object with the light transmitting body 5. The absorption of a single photon triggers a large avalanche current. According to this embodiment the data processing unit 9 is further configured to calculate the applied force during the physical contact of the object with the interaction surface of the light transmitting body 5 on the basis of the signals received from the light detector 4, corresponding to the number of sensors activated in the multiple light detector arrangement due to light transmitting body’s 5 deformation along the depth axis, z-axis of the light transmitting body (5), which is perpendicular to the designated interaction surface, as a result of the physical contact of the object with the interaction surface of the light transmitting body 5. The time between the emission of the photons and the avalanche (Time of flight) is measured and translated into a target distance in the range result register.

[0016] The data processing unit 9 may be further configured to analyze the temporal sequence of activation of the individual time of flight sensors 2 in the array 8 within the multiple light detector arrangement, enabling the determination of a time coordinates associated with the physical contact, such to record the moment of contact, thereby providing a time analysis of interactions with the light transmitting body 5.

[0017] According to yet another embodiment, the system may comprise two or more sensor sets 20; wherein the sensor sets 20 are positioned at predetermined locations around the periphery of the light transmitting body 5, enabling coverage of the entire designated interaction surface, allowing for detection of x, y, z coordinates of physical contact on the designated interaction surface of the light transmitting body 5 (Fig.3A, 4A, 6A, 6B, 6C, 6D and 7), wherein the z-coordinate represents the pressure applied during the physical contact. According to yet another embodiment, the system may further comprise a sequence controller 7 operably connected with each time of flight sensor 2 in the sensor sets 20 and with the data processing unit 9, wherein the sequence controller 7 is configured to controllably switch on the light sources 3 of the time of flight sensors 2 at a required time and provide the data processing unit 9 a timing information on when each of the light sources 3 emit light signals. According to yet another embodiment, the sequence controller 7 may be further configured to provide each light source 3 of each time-of-flight sensor 2 an electrical modulation signals for subsequent emission by the light sources 3 of electrically modulated light. The modulation of the light sources 3 is preferably synchronized or adjusted based on the position of each sensor 2 to reduce interference and improve spatial and temporal resolution for detecting physical contact points on the light transmitting body 5.

[0018] Contact coordinate estimation. The distance L between designated interaction surface of the light transmitting body 5 and the light detector 4 is obtained through the photon travel time t measurement starting from the moment when the light has been transmitted from the light source 3, reflected from the designated interaction surface of the light transmitting body 5 and detected by the light detector 4, and by knowing the refractive index n of the light transmitting body 5 at the wavelength λ of the light emitted by the light source 3 since the speed of light c in the light transmitting body 5is lower with respect to the speed of light in the air: The time between the emission of the photons and the avalanche (time of flight) is measured and translated into a target distance in the range result register. The distance measurements are then transformed, using a data processing algorithm at the data processing unit 9, to the two-dimensional coordinates on the light transmitting body 5 to identify contact points. Additionally, this can be obtained by using the programmable region of interest (ROI) of the time-of-flight sensor 2.

[0019] Due to the time-of-flight measurements from the moment when the light has been transmitted from the light source 3, reflected from the object in contact with the light transmitting body 5 and detected by the detector 4, the position of the object in contact is obtained. The observation of the contact point is lateral like given in Fig.1A- 1B (i.e. the observation is not made from the side that is directly across from where the contact occurs, but rather from a side perspective, providing a lateral view of the contact point). This solution permits development of less bulky physical contact and / or pressure sensor with the use of lower number of light sources and detectors thus reducing the price of the sensor and reducing the energy consumption of the sensor.

[0020] The system is also capable to detect the temporal coordinates of the physical contact of an object with the light transmitting body 5, besides the spatial ones. The data processing unit 9 is further configured to analyse the temporal sequence of activation of one or more time of flight sensors 2 and compare it with the temporal sequence of the activation of one or more light emitters 3, enabling the determination of a time coordinates associated with the physical contact, such to record the moment of contact, thereby providing a time analysis of interactions with the light transmitting body 5 (Fig.5). Recording the exact moment of contact adds temporal resolution to the data, which can be crucial for applications requiring understanding not just where and how an object interacts with the surface, but also when. It also allows for the analysis of dynamic interactions over time, which can be important in applications like touch- sensitive interfaces, where the sequence and timing of touches can convey different inputs or commands. By adding a time dimension, the system can provide a richer dataset, which can be valuable for complex analyses, such as studying the kinetics of an interaction or tracking fast-moving objects.

[0021] Each time of flight sensor 2, depending on the model and on the sensor working mode, may capture simultaneously one or more than one time of flight measurements, distributed on an array 8 covering the detector 4 zone (field of view) of the sensor 2, providing three-dimensional data (x,y,t), considering the two-dimensional array position (x,y) and the time of flight t measured from the light source 3 to the specific element within the array 8 on the sensor 2. This three dimensional data (x,y,t) are transformed as well, using a data processing algorithm at the data processing unit 9 to the two-dimensional coordinates (x,y) on the light transmitting body 5, achieving increased resolution on the detection of contact points. Additionally, in the case of a mechanically elastic light transmitting body 5, the (x,y,t) measurements at the array 8 might be transformed, using another data processing algorithm at the data processing unit 9, into three dimensional data (x,y,z) where the additional dimension z corresponds to surface deformation (pressure) of the contact point.

[0022] A single light transmitting body 5 might be explored by one or more time of flight sensors 2 with different positioning with respect to the light transmitting body 5. Figure 3A illustrates a particular embodiment of five time of flight sensors 2 positioned within the light transmitting body 5 in the shape of a rectangle in such a way that the light source’s 3 and light detector’s 4 exclusion zones are practically not overlapping, ensuring and adequate coverage of the surface of the light transmitting body 5. The embodiment structure might be larger of shorter at any of the two dimensions, and the number of time of flight sensors 2 might be larger or lower, adapted to the shape of the light transmitting body 5. A schematic diagram for detecting the contact point using the light transmitting body 5 with five time of flight sensors 2 with non-overlapping light source 3 and light detector 4 exclusion zones (as shown in the Fig.3A) is given in the Figure 3B. The system may include a sequence controller 7 to switch on the different light sources 3 at a known time. The sequence controller 7 may also initiate the sensing at each detector 4 at a known time. The sequence controller 7 provides the information of the temporal timestamps for the switching of light sources 3 to each time of flight sensor 2, for an adequate measurement of the time of flight t. Each of the time of flight light detector 4 may measure into an array 8 represented as sensor array (Fig.3B), providing three dimensional data (x,y,t) for each light source 3 and for each time of flight sensor 2. The combination of all these three-dimensional data can be transformed, using a processing algorithm at the data processing unit 9, into contact points on the surface of the light transmitting body 5, and might provide as well pressure (deformation) information.

[0023] Besides improving the surface coverage (Fig 3), the embodiment of multiple time of flight sensors 2 can also increase the resolution of contact detection on the light transmitting body 5. Figure 4A shows an illustrative image in which the positions of the time of flight sensors 2 ensure overlapping detection areas between each pair of sensor. All the considerations for schematic diagram for detecting the contact point using the light transmitting body 5 with four time of flight sensors 2 given in Fig.4B are the same as described for Fig.3B. The presence of the sequence controller 7 may be useful to increase the accuracy of the contact zone coordinate detection since the light detectors 4 of plurality of time of flight sensors 2 might detect contact on the same areas of the light transmitting body 5. The sequence controller 7 may decrease the cross-talks between plurality of time of flight sensors 2 like for configuration given in Fig.4A where the light source’s 3 and the detector’s 4 exclusion zones of different time of flight sensors are overlapping. The sequence controller 7 may also reduce energy consumption by not keeping on all time of flight sensors simultaneously. The algorithm at the data processing unit 9 might consider the overlap of the detection areas of multiple time of flight detectors 4 to provide more resolution on the detection of contact and pressure on the light transmitting body 5.

[0024] The configurations of optical tactile and pressure sensor 1 distribution given in Fig.3A and Fig.4A are a non-limiting: for any needs, specific geometrical requirements the form of light transmitting body 5 can be varied, and positions and number of time of flight sensors 2 can be different and can be varied. As a result, also a schematic diagram for detecting the contact point given in Fig.3B or Fig. 4B can be modified by adding or removing matrix arrays, sequence controllers, processors, timer and other electronic components.

[0025] The system may be composed of several optical tactile sensors and a robot. Each optical tactile sensor may comprise a single light transmitting body and one or more time of flight devices. Optical tactile sensors can be attached to different surface regions of different sizes of the same sensorized surface. Each optical tactile sensor detects contact and pressure for its own surface region, independently of other sensors in the same system. The system may further comprise one or more output devices, such as displays, speakers, headphones, projectors, printers, wearable displays and other wearable devices. It may also include one or more input devices, such as keyboard, mouse, disk / media drive, memory card, memory stick / thumb-drive, biometric scanner, pen, touch-input device, voice / auditory input device, motion detector, camera, scale etc. The data processing unit 9 may be used for a single optical tactile sensor or shared among several optical sensors. The data processing unit 9 may include the sequence controller 7. The data processing unit 9 may be associated with a computer readable storage medium, comprising a plurality of computer readable mediums, network interphases and cloud network. The network interphase may include an antenna, a modem, LAN port, WI-FI cars, WiMAxcars, mobile communication hardware, near-field communication hardware, satellite communication hardware and / or any wired or wireless hardware for communication with other networks and / or devices.

[0026] Fig.5 illustrates a flowchart for detecting the contact point coordinates with and without applied force estimation on the light transmitting body 5 using a plurality of time of flight light sources 3 and light detectors 4, according to embodiments shown and described herein. A controller of the time of flight sensor 2 instructs each of the plurality of time of flight light sources 3 to emit signals at almost simultaneously times or at different times from the rest of the plurality of time of flight light sources 3. The light emission at different times can be useful for the time of flight sensor 2 configuration where light sources’ 3 signals and light detectors’ 4 field of view are overlapping between different time of flight sensors (as shown in Fig.4A). At the next step, a light detector 4 one receives the signal which is emitted by the emitter 3 of the time of flight sensor 2 one, the collector 4 of time of flight sensor 2 two receives the signal which is emitted by the light source 3 of the time of flight sensor 2 two, etc. If physical contact appears, the next step takes place, where the data processing unit 9 obtained a plurality of three-dimensional or four-dimensional raw data based on the signals. Otherwise, a flowchart returns to the first step. The raw data of third step are not considered or considered as a bassline in case of absence of any physical contact. The fifth step comprises data analysis and processing to provide contact zone coordinates with or without applied force to the light transmitting body 5 surface. If another physical contact appears the flowchart returns to step four, otherwise it goes to step six and returns to the first step. It should be noted that the optical tactile sensing is when optical tactile sensor 1 is continuously in working condition.

[0027] The light transmitting body 5 can be any light transmitting body 5 or light transmitting bodies 5 which are transparent for the wavelength of the time of flight sensors’ 2 light source 3. The light transmitting body 5 can be a gel, such as silicon or other rubber-like substances, it can be solid silicon and may be cast in a given shape before assembly on objects to be sensorized. The light transmitting body 5 can be made also of two or more light transmitting bodies 5, e.g., it can be any plastic container filled with a liquid or gas. It can be also an optical fiber or a light guide made of any plastic or glass and covered with another transparent light transmitting body 5 with refractive index greater or lower than the refractive index of the fiber or light guide. The typical wavelengths of commercial time of flights light sources 3 are 900-950 nm, but not limited to this range. The wavelength can be even in the visible spectral range or in the deeper IR above 950 nm. Both optically transparent and opaque polymers with light extinction coefficient equal or near zero at the time of flight emitter wavelengths can be used as light transmitting body 5 to transmit time of flight light (e.g., polycarbonate- PC, polyethylene-PE, polyvinyl chloride-PVC, Poly(methyl methacrylate)-PMMA, polysiloxane, silicone rubber). The light transmitting body 5 can be of any shape and thickness to adapt to the geometrical form of the object to be sensoriezed. For example, if the floor has to be sensorized with the tactile and / or pressure sensor, the polymer sheets of several mm thickness could be used. In case of the non-planar surface such as robot arms, the light transmitting body 5 sheets are developed in the proper shape to accommodate the robot arm.

[0028] Fig.6ABCD show a robot arm as a cylinder 13 and the light transmitting body 5 sheet is wrapped around the cylinder with plurality of time of flight sensors 2 integrated into the light transmitting body 5. The light transmitting body 5 can be also an optical fiber or light guide, which is wrapped around the cylinder, e.g. as shown in Fig.7. The light transmitting body 5 shapes are not limited to those shown in Fig.6ABCD and 7.

[0029] A proof of concept experiments were made as designed in the Fig.8-12. The time of flight sensor 2 VL53L0X with λ = 940 nm was attached to the empty PP box 14 with length of 157 mm. The measurement in the air was performed (Fig. 8). Then the box was filled with the light transmitting body 5 - water with n = 1.356. The measurement in the water was performed (Fig.9). Then an object in the form of a cylinder 16 having a dimeter 10 mm, length 20 mm, was positioned on the surface of the water (not entering inside the water) in the field of view of the time of flight sensor 2 and measurement was performed (Fig. 10). An experiment was also performed with the light transmitting body 5 made of silicon rubber (Fig.11A) and the light transmitting body 5 made of PMMA in the form of waveguide (Fig. 12A) with 7 mm diameter and 100 mm length. In these particular experiments, no SPAD array has been used, thus only x coordinate is presented. The Figure 11B illustrates the contact point accruing during experiment shown in Figure 11A. The Figure 12B illustrates signal received during the contact point in the experiment given in the Figure 12A. These simple experiments demonstrate that optical tactile sensor 1 can be realized by time of flight sensor 2 coupling with light transmitting body 5 which permits time of flight light transmittance. During the physical contact the internal light reflection inside the light transmitting body 5 are changing permitting contact zone detection by time of flight sensor(s) 2 lateral view on the light transmitting body 5. The Table 1 given below compares the actual distances with the measured distances L.

[0030] Table 1. Comparison of actual distances with the distances measured by the claimed device Experiment Actual L, mm Measured L, mm (Fig.11) - empty box 157 157 ± 2 (Fig.12) - box filled with water157 157 ± 11ExperimentActual L to contactzone, mm Measured L, mm(Fig.13) - cylinder on the surface of the water75 73 ± 15(Fig. 14) - silicon rubber 25 22 ± 535 33 ± 55049 ± 1(Fig.15) - PMMA light guide 80 90 ± 10 120 142 ± 22

Claims

Claims 1. An optical tactile sensor (1) capable of detecting the position of physical contact, the sensor (1) comprising, a light transmitting body (5), defining a designated interaction surface; the light transmitting body (5) having at least two opposite relatively larger interaction surfaces (5`) and multiple smaller edge surfaces (5``) positioned between the larger interaction surfaces (5`); a time-of-flight sensor (2) comprising a light source (3) designed to emit light pulses with a duration in the sub-nanosecond range, and a light detector (4); wherein the light source (3) and the detector (4) are located on one and the same smaller edge surface (5``) of the light transmitting body (5); wherein the light transmitting body (5) is configured to enable lateral propagation of light emitted from the light source (3) at multiple incident angles, reflecting internally across the larger interaction surfaces (5') as the light propagates through the light transmitting body (5), and wherein the light detector (4) is designed to detect the same light signal originally emitted by the light source (3) after it is reflected from at least one interaction surface of the light transmitting body (5) during physical contact with an object, and subsequently directed back towards the light detector (4) through controlled internal reflection, capturing the time-of-flight measurements of the emitted light signals at multiple incident angles within the light transmitting body (5).

2. The sensor of any preceding claims, wherein the light transmitting body (5) is mechanically elastic.

3. The sensor of any preceding claims, wherein the light transmitting body (5) is mechanically rigid.

4. The sensor of any preceding claims, wherein the light transmitting body (5) has a refractive index n in the range from 1 to 3, an extinction coefficient k less than 0.01, and a scattering coefficient less than 0.5 cm-1at the wavelength of the light source (3).

5. The sensor of any preceding claims, wherein the sensor (1) is further configured to be placed on planar or non-planar contact surface.

6. An optical tactile sensor (1) system comprising a data processing unit (9); a light transmitting body (5), defining a designated interaction surface; the light transmitting body (5) having at least two opposite relatively larger interaction surfaces (5`) and multiple smaller edge surfaces (5``) between the larger interaction surfaces; one or more sets (20) of the time-of-flight sensors (2), each comprising a light source (3), and a light detector (4); wherein the light source (3) and the detector (4) are located adjacent on one and the same smaller edge surface (5``) of the light transmitting body (5); wherein the light transmitting body (5) is situated in a manner that allows the light emitted from the light source (3) to propagate through it laterally, wherein the light detector (4) is designed to detect the emitted light signal, which is reflected from at least one light transmitting body’s (5) interaction surface during the physical contact of an object with the light transmitting body (5) interaction surface and is subsequently directed back towards the light detector (4) through controlled internal reflection within the light transmitting body (5); wherein the data processing unit (9) configured to receive data from the sensors (2) sets (20) and analyse time interval measurements received from the sensors (2) sets (20) to determine physical contact position by calculating the distance between the sensors (2) set (20) and the point of contact, based on the time it takes for the light to travel from the light source (3) to the point of contact and from the point of contact to light detector (4).

7. The system of claim 6, wherein the light detector (4) is designed as multiple light detector arrangement comprising an array of sensors, each configured with single- photon detection capability to detect photons that have been reflected from different points of the light transmitting body’s (5) interaction surface during the physical contact of an object with the light transmitting body’s (5) interaction surface; and the data processing unit (9) is further configured to calculate the applied force during the physical contact of the object with the interaction surface of the light transmitting body (5) on the basis of the signals received from the light detector (4), corresponding to the number of sensors activated in the multiple light detector arrangement due to light transmitting body’s (5) deformation along the depth axis, z-axis of the light transmitting body (5), which is perpendicular to the designated interaction surface, asa result of the physical contact of the object with the interaction surface of the light transmitting body (5).

8. The system of claim 7, wherein the data processing unit (9) is further configured to analyze the temporal sequence of activations among the individual time of flight sensors (2) within the array of the multiple light detector arrangement, enabling the determination of a time coordinate associated with each physical contact, thereby recording the moment of contact and providing a time-based analysis of interactions with the light transmitting body (5).

9. The system of claim 6, comprising two or more sensor sets (20); wherein the sensor sets (20) are positioned at predetermined locations around the periphery of the light transmitting body (5), enabling coverage of the entire designated interaction surface, allowing for detection of x, y, z coordinates of physical contact on the designated interaction surface of the light transmitting body (5), wherein the z-coordinate represents the pressure applied during the physical contact.

10. The system of claim 9, further comprising a sequence controller (7) operably connected with each time of flight sensor (2) in the sensor sets (20) and with the data processing unit (9), wherein the sequence controller (7) is configured to controllably switch on the light sources (3) of the time of flight sensors (2) at a required time and provide the data processing unit (9) a timing information on when each of the light sources (3) emit light signals.

11. The system of claim 10, wherein the sequence controller (7) is further configured to provide each light source (3) of each time-of-flight sensor (2) an electrical modulation signal for subsequent emission by the light sources (3) of electrically modulated light, wherein the modulation of the light sources (3) is synchronized or adjusted based on the position of each sensor (2) to reduce interference and improve spatial and temporal resolution for detecting physical contact points on the light transmitting body (5).

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