Acoustic detection and ranging sensors

Abstract

An acoustic detection and ranging sensor (20) comprises an acoustic transmitter (21) configured to emit a diverging acoustic signal, a first acoustic receiver (23) and a second acoustic receiver (25). The first acoustic receiver (23) is arranged in a first plane, and is configured to receive reflections of the acoustic signal from one or more surfaces in a vicinity of the sensor (20). The second acoustic receiver (25) is arranged in a second plane that is nonparallel with the first plane, and is configured to receive the reflections of the acoustic signal. The field of view of the first acoustic receiver (23) and the field of view of the second acoustic receiver (25) partially overlap such that the field of view of the acoustic detection and ranging sensor (20) is greater than 180 degrees.

Description

[0001] 496.135.173120 / 01 - 1 -

[0002] Acoustic Detection and Ranging Sensors

[0003] TECHNICAL FIELD

[0004] This disclosure relates to acoustic detection and ranging (ADAR) sensors, particularly, although not exclusively, for autonomous mobile robots.

[0005] BACKGROUND OF THE INVENTION

[0006] It is known to use ADAR sensors to detect people or objects in the vicinity of the ADAR sensors. For example, it is well-known for cars to include an acoustic parking sensor system to detect the presence of obstacles in proximity of the car while it is being parked. ADAR systems may also be employed on autonomous mobile robots (AM Rs) to aid with navigation and obstacle detection.

[0007] However, the Applicant has recognised that existing ADAR sensors are only able to detect objects in front of the ADAR sensor in a 180-degree by 180-degree field of view. As a result, multiple independent ADAR sensors are typically required, e.g. to allow for object detection on all sides of an autonomous mobile robot.

[0008] SUMMARY OF THE INVENTION

[0009] According to a first aspect of the invention, there is provided an acoustic detection and ranging sensor comprising: an acoustic transmitter configured to emit a diverging acoustic signal; a first acoustic receiver arranged in a first plane, configured to receive reflections of the acoustic signal from one or more surfaces in a vicinity of the sensor; a second acoustic receiver arranged in a second plane that is nonparallel with the first plane, configured to receive the reflections of the acoustic signal; wherein the field of view of the first acoustic receiver and the field of view of the second acoustic receiver partially overlap such that the field of view of the acoustic detection and ranging sensor is greater than 180 degrees.

[0010] According to a second aspect of the invention, there is provided a method of operating an acoustic detection and ranging sensor, the method comprising: emitting a diverging signal from an acoustic transmitter; 496.135.173120 / 01 - 2 - receiving reflections of the acoustic signal from one or more surfaces in a vicinity of the sensor at a first acoustic receiver arranged in a first plane; and receiving the reflections of the acoustic signal at a second acoustic receiver arranged in a second plane that is nonparallel with the first plane; wherein the field of view of the first acoustic receiver and the field of view of the second acoustic receiver partially overlap such that the field of view of the acoustic detection and ranging sensor is greater than 180 degrees.

[0011] Thus it will be seen that, in accordance with the invention, an acoustic detection and ranging (ADAR) sensor is provided having a field of view greater than 180 degrees. This is achieved using two acoustic receivers arranged on non-parallel planes and having overlapping fields of view that receive reflections of the same acoustic signal from a common transmitter. As the same acoustic signal is received at both the first and second acoustic receivers, angular analysis can be performed on reflected acoustic signals received at the first and second receivers, rather than requiring that the emitted acoustic signals be steered in different directions at different times, as is conventional. ADAR sensors in accordance with the present invention are therefore able to sense objects over a field of view of greater than 180 degrees using acoustic signals emitted by a single transmitter.

[0012] In some embodiments, the first and second planes are substantially perpendicular, such that the first and second receivers are arranged on respective perpendicular planes either side of a corner formed where the two planes meet. However, this is not essential and the angle between the first and second planes may be greater or less than 90 degrees in other embodiments.

[0013] In some embodiments, the transmitter comprises at least a first transmit element (e.g. an acoustic transducer) located on the first plane and at least a second transmit element located on the second plane. The first transmit element may be located on a first surface in the first plane, and the second transmit element may be located on a second surface in the second plane.

[0014] In some embodiments, the transmitter comprises a plurality of transmit elements located on the first plane and / or a plurality of transmitters located on the second plane. The transmit elements may be provided on the first plane and / or the second 496.135.173120 / 01 - 3 - plane in respective arrays, and may be spaced at a fixed interval on the first plane and / or the second plane respectively. Beamforming may be performed to construct a virtual source of acoustic signals between them - e.g. so that the transmit elements are symmetrically arranged with respect to the virtual source along at least one axis. For example, the virtual source may be located at a point that is equidistant from two or more of the transmit elements.

[0015] In some embodiments, the transmit elements of the first array are located on the first surface in the first plane and / or the transmit elements of the second array are located on the second surface in the second plane. In some such embodiments, the transmit elements of each array are linearly spaced along the surface on which the array is located. The spacing of the transmit elements may be dependent on the wavelength of the acoustic signal to be transmitted. For example, the transmit elements may be spaced such that the wavelength of the transmitted acoustic signals is approximately equal to twice the spacing between the elements.

[0016] In some embodiments in which the transmitter comprises transmit elements on the first plane and the second plane, beamforming is used to construct a virtual source of acoustic signals between them. This may comprise steering the phase of acoustic signals emitted by the transmit elements so as to achieve a diverging wave in the far field.

[0017] In some other embodiments, the acoustic transmitter is located between the first plane and the second plane. The acoustic transmitter may be located between the first and second transmit elements. For example, the acoustic transmitter may be located at or proximate to the corner between the first plane and the second plane. In some embodiments, the transmitter may be located at or proximate to the intersection between a first surface in the first plane and a second surface in the second plane. For example, the transmitter may be provided in a recessed region provided at the intersection between the two surfaces.

[0018] In some embodiments, the transmitter between the first plane and the second plane comprises a single transmit element (e.g. a single acoustic transducer) which emits an acoustic signal, provided that sufficient sound pressure can be generated by the single transmit element. The transmit element may be configured to emit an 496.135.173120 / 01 - 4 - acoustic signal through an outlet. The size of the outlet (e.g. the diameter of the outlet) may be selected to provide a balance between directionality and strength of the emitted acoustic signal. If the diameter of the outlet is large with respect to the wavelength of the emitted signal, the emitted signal is directional, while if the diameter of the outlet is too small with respect to the wavelength of the emitted signal, the emitted energy is low. In some embodiments, the diameter of the outlet is small with respect to the wavelength of the emitted signal. The diameter of the outlet may be between 10% and 60% of the wavelength, optionally between 15% and 40% of the wavelength, further optionally between 25% and 30% of the wavelength. In some embodiments the wavelength is approximately 25% of the wavelength of the emitted acoustic signal.

[0019] However, in some embodiments, the transmitter comprises a plurality of transmit elements. The transmit elements may be positioned along the intersection between the first plane and the second plane. For example, the transmit elements may be provided in respective recessed regions along the intersection between a first surface in the first plane and a second surface in the second plane. Each transmit element may be configured to emit an acoustic signal through a respective outlet. The size of the outlet (e.g. the diameter of the outlet) may be selected to provide a balance between directionality and strength of the emitted acoustic signal as described above. In some embodiments, the diameter of the outlet is between 10% and 60% of the wavelength, optionally between 15% and 40% of the wavelength, further optionally between 20% and 30% of the wavelength. In some embodiments the wavelength is approximately 25% of the wavelength of the emitted acoustic signal.

[0020] The plurality of transmit elements may be spaced at intervals in an array, e.g. the transmit elements may be uniformly spaced apart along the intersection between the first plane and the second plane. The spacing of the transmit elements may be dependent on the wavelength of the acoustic signal to be transmitted by the transmitter. For example, the transmit elements may be spaced such that the wavelength of the transmitted acoustic signals is approximately equal to twice the spacing between the transmit elements. 496.135.173120 / 01 - 5 -

[0021] In some embodiments in which the transmitter comprises a plurality of transmit elements positioned along the intersection between the first plane and the second plane, beamforming of the emitted acoustic signals may be performed so as to achieve a diverging wave in the far field. Beamforming of the emitted acoustic signals may comprise controlling the phase of acoustic signals transmitted by the transmit elements as to achieve a diverging wave in the far field.

[0022] In some embodiments, the first receiver is located on a first surface in the first plane, and the second receiver is located on a second surface in the second plane.

[0023] In some embodiments, the first acoustic receiver and the second acoustic receiver are substantially identical. In some embodiments, the first acoustic receiver and / or the second acoustic receiver comprise an array of acoustic receive elements (e.g. microphones). Thus, in some embodiments, each receiver may comprise a respective array of receive elements.

[0024] In some embodiments, the array of receive elements comprises a plurality of receive elements arranged in a linear or two-dimensional array. The two- dimensional array may comprise a first linear array and a second linear array, the first and second linear arrays extending along perpendicular axes. The first and second linear arrays may intersect. The two-dimensional array may comprise at least one additional receive element located at a position that is offset from the first and second linear arrays.

[0025] In some embodiments, the first and second linear arrays are arranged in a cross shape. The cross-shaped array of receive elements may comprise additional receive elements located at one or more diagonals of the cross-shaped array. Providing receive elements on one or more diagonals of the array may allow the receiver to resolve ambiguities in surface positions in the event that two or more surfaces are located at the same range from the receive elements.

[0026] In some embodiments in which the array is a linear array, the receive elements of the array are arranged in a repeating pattern. The receive elements of the array may be arranged such that there is a constant pitch between the receive elements. 496.135.173120 / 01 - 6 -

[0027] In some such embodiments, the number of receive elements in the linear array may be between three and sixteen.

[0028] In some embodiments in which the array is a 2D array, the receive elements of the array are arranged in a repeating pattern along at least one axis (i.e. one dimension). The receive elements of the array along the at least one axis may be arranged such that there is a constant pitch between the receive elements. The number of receive elements along each axis of the 2D array may be a respective number between 8 and 16. The number of receive elements along each axis (i.e. each dimension) of the 2D array may be identical, however in some alternative embodiments the number of receive elements is different along the two axes. This may allow for greater resolution to be achieved along one axis than the other, e.g. to reduce the amount of processing required along an axis for which low angular resolution is acceptable. In some embodiments, the pitch between receive elements of the 2D array is between 0.85 mm and 25 mm, preferably between 1.8 mm and 10 mm.

[0029] In some embodiments, the acoustic detection and ranging sensor further comprises a processing system. The processing system may be configured to control the acoustic transmitter to cause it to emit the diverging acoustic signal. The processing system may be configured to sample electrical signals output by the first and second acoustic receivers in response to the received reflections of the acoustic signal, and to process the sampled electrical signals to identify the one or more surfaces in the environment. In some embodiments, processing the sampled electrical signals comprises determining a range and / or a position for each of the identified surfaces. Determining a range for each surface may comprise determining a time-of-flight for the reflected acoustic signal from the respective surface.

[0030] In some embodiments, emitting the acoustic signal comprises applying time division multiplexing or frequency division multiplexing to the emitted signal. This may allow the ADAR sensor to address issues with coexistence if multiple ADAR sensors are operating in the same area. 496.135.173120 / 01 - 7 -

[0031] In some embodiments, the emitted acoustic signal comprises a chirp signal. The chirp signal may comprise an upward chirp or a downward chirp. In some embodiments, the chirp signal comprises both an upward chirp and a downward chirp.

[0032] In some embodiments, the emitted acoustic signal comprises a coded signal. In some such embodiments, emitting the acoustic signal may comprise emitting a plurality of differently coded signals in different directions from the ADAR sensor.

[0033] The acoustic transmitter could transmit audible acoustic signals but in a set of embodiments it is an ultrasonic transmitter. The transmitter may, for example emit at a frequency or frequencies greater than 20 kHz, e.g. greater than 30 kHz.

[0034] According to a third aspect of the invention, there is provided a device comprising the acoustic detection and ranging sensor of the first aspect.

[0035] Where the acoustic detection and ranging sensor forms part of a device according to the third aspect, the device may be a mobile device. For example, the device may be a mobile robot, preferably an autonomous mobile robot. However, in some embodiments, the device may be a static device that has a component that is moveable, e.g. using an actuator, such as a robot arm. In some embodiments, the ADAR sensor may be provided at or proximate to a corner of the device. In some embodiments, the device may be provided with a respective ADAR sensor on or proximate to each of at least two corners of the device, preferably on or proximate to at least two diagonally opposed corners. This may allow for a 360-degree field of view around the device to be achieved using only two ADAR sensors in accordance with the present invention.

[0036] Thus, in some embodiments, the device may further comprise a second acoustic detection and ranging sensor comprising: a second acoustic transmitter configured to emit a second diverging acoustic signal; a third acoustic receiver arranged in a third plane, configured to receive reflections of the second acoustic signal from one or more surfaces in a vicinity of the sensor; 496.135.173120 / 01 - 8 - a fourth acoustic receiver arranged in a fourth plane that is nonparallel with the third plane, configured to receive the reflections of the second acoustic signal; wherein the field of view of the third acoustic receiver and the field of view of the fourth acoustic receiver partially overlap such that the field of view of the second acoustic detection and ranging sensor is greater than 180 degrees.

[0037] Features of any aspect or embodiment described herein may, wherever appropriate, be applied to any other aspect or embodiment described herein. Where reference is made to different embodiments or sets of embodiments, it should be understood that these are not necessarily distinct but may overlap.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Certain preferred embodiments of this disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0040] FIG. 1 is a schematic illustration of an autonomous mobile robot employing an acoustic detection and ranging sensor according to a prior art arrangement;

[0041] FIG. 2 is a schematic illustration of an autonomous mobile robot employing an acoustic detection and ranging sensor according to a first embodiment of the present invention;

[0042] FIG. 3 is a more detailed schematic illustration of the acoustic detection and ranging sensor according to the first embodiment of the present invention;

[0043] FIG. 4 is a further schematic illustration of the acoustic detection and ranging sensor according to the first embodiment of the present invention;

[0044] FIG. 5 is a schematic illustration of a transmitter of the acoustic detection and ranging sensor of the first embodiment of the present invention;

[0045] FIG. 6A is a schematic illustration of an acoustic detection and ranging sensor according to a second embodiment of the invention;

[0046] FIG. 6B is a schematic illustration of a transmitter of the acoustic detection and ranging sensor according to a second embodiment of the invention;

[0047] FIG. 7A is a schematic illustration of an acoustic detection and ranging sensor according to a third embodiment of the invention;

[0048] FIG. 7B is a schematic illustration of a transmitter of the acoustic detection and ranging sensor according to the third embodiment of the invention; and

[0049] FIG. 8 is a schematic illustration of an autonomous mobile robot employing two acoustic detection and ranging sensors in accordance with the present invention. 496.135.173120 / 01 - 9 -

[0050] DETAILED DESCRIPTION

[0051] Figure 1 shows an autonomous mobile robot (AMR) 1 comprising an acoustic detection and ranging (ADAR) sensor 2 according to the prior art. The ADAR sensor 2 is mounted to a surface at the front of the AMR 1 and is configured to emit acoustic signals into the environment in the vicinity of the AMR 1 and to receive reflections of the acoustic signals from objects or people in the environment.

[0052] The received acoustic signals are sampled by a processing system 3 and are processed to identify objects in the environment. Movement of the AMR 1 is then controlled based on the identified objects, e.g. to ensure that collisions with objects are avoided as the AMR 1 moves through the environment.

[0053] As shown in Figure 1, the ADAR sensor 2 has a field of view 4 covering a range of only up to 180 degrees in front of the AMR 1. As a result, the ADAR sensor 2 is unable to detect objects located at the sides of the AMR 1 or behind the AMR 1 , meaning that additional ADAR sensors would be required in order to detect objects or people in these locations. This issue is addressed, in certain prior art arrangements, by providing one or more additional ADAR sensors on other surfaces of the AMR in order to improve the likelihood of detecting objects in directions the AMR is likely to move.

[0054] For example, in certain prior art arrangements, an ADAR sensor may be provided on each of the front and back surfaces of an AMR to detect objects as the AMR moves forwards or backwards in the environment. However, as each ADAR sensor has a field of view of <180 degrees, there remain regions at the sides of the AMR in which object cannot be detected. While additional ADAR sensors could be provided at the sides of the AMR to prevent this, such an approach may be prohibitively expensive in certain applications, or may not be possible due to size or weight constraints on the AMR.

[0055] Figure 2 shows an AMR 10 comprising an ADAR sensor 20 according to a first embodiment of the present invention. The ADAR sensor 20 is mounted at a corner at the front of the AMR 10 and emits acoustic signals into the environment in the 496.135.173120 / 01 - 10 - vicinity of the AMR 10 and receives reflections from objects or people in the environment. The received acoustic signals are sampled by a processing system 30 and are processed to identify the objects in the environment as explained above in relation to Figure 1.

[0056] In contrast to the prior art ADAR sensor 2 shown in Figure 1 , the ADAR sensor 20 has a field of view 40 that extends approximately 270 degrees around the corner of the AMR 10, allowing for objects to be detected both in a 180-degree window in front of the AMR 10, as well as to one side of the AMR 10, using a single ADAR sensor 20, as explained in the following.

[0057] Figure 3 schematically illustrates the ADAR sensor 20 in more detail. It comprises a first ultrasonic receiver 23 and a second ultrasonic receiver 25, located on perpendicular surfaces of the ADAR sensor 20, and a transmitter 21 located between the two receivers proximate to the intersection of the two surfaces (i.e. at the corner between the surfaces). The ADAR system 20 also comprises control electronics 27 and a controller 29 that controls the control electronics 27. The control electronics 27 comprises drive circuitry for driving the transmitter 21, including a digital to analogue converter (DAC) and an amplifier for providing drive signals from the controller 29 to the transmitter 21. The control electronics 27 also comprises receive circuitry for processing acoustic signals received at the receivers 23 and 25, including an analogue to digital converter (ADC) for sampling electrical signals output by the receivers 23 and 25 in response to received acoustic signals and providing an output to the controller 29, and optionally one or more filters.

[0058] The transmitter 21 emits a diverging acoustic signal into the environment, where it is reflected from surfaces of objects or people within the environment. The first and second ultrasonic receivers 23 and 25 receive the reflected acoustic signals, and have respective fields of view 41 , 42 that partially overlap such that the field of view of the ADAR sensor 20 is greater than 180 degrees (e.g. 270 degrees in the embodiment shown in Figure 3).

[0059] The ADAR sensor 20 is shown in more detail in Figure 4. The transmitter 21 of the

[0060] ADAR sensor 20 comprises two sets of transmit elements (e.g. ultrasound transducers) 211 located on perpendicular surfaces 230, 250 of the ADAR sensor 496.135.173120 / 01 - 11 -

[0061] 20. As explained in more detail below, beamforming of acoustic signals emitted by the transmit elements 211 is performed to construct a virtual source between them so that the transmit elements are symmetrically arranged about the virtual source, and which emits an acoustic signal with a diverging spherical waveform in the far- field.

[0062] The ultrasonic receivers 23, 25 are located on respective surfaces 230, 250 of the ADAR sensor 20, and each comprise a respective set of receive elements 231 , 251 arranged in a cross, as well as an additional receive element 232, 252 located at the diagonal of the cross of the respective receivers 23, 25.

[0063] The distribution of receive elements 231 , 251 along each perpendicular axis of the cross can be set based on the nature and distribution of objects to be detected using the ADAR sensor 20. In general, a greater number of receive elements along a given axis allows for a greater number of objects along said axis to be distinguished from one another. For example, vertical poles are best distinguished by a large number of receive elements in the horizontal direction, whereas horizontal poles are best distinguished by a large number of receive elements in the vertical direction. The additional receive elements 232, 252 located at the diagonal of the cross serves to resolve ambiguities by allowing pairing of x and y coordinates identified using the receivers of perpendicular axes.

[0064] Figure 5 shows a sectioned view of the transmitter 21 of the ADAR sensor 20 of the first embodiment in more detail. As shown in Figure 4, transmit elements 211 are arranged on the two perpendicular surfaces 230, 250 of the ADAR sensor 20. Although two transmit elements 211 are shown in the embodiment of Figure 4, it will be appreciated that additional transmit elements may be provided in some embodiments, such that a plurality of transmit elements extend along each surface in a respective array.

[0065] The spacing between the transmit elements 211 is set based on the wavelength of the acoustic signals 212 to be emitted, such that the spacing between the transmit elements 211 on each surface is approximately half of the wavelength of the acoustic signals. Each transmit element 211 generates and emits an acoustic signal through a respective outlet. In the embodiment shown in Figure 5, each outlet has a 496.135.173120 / 01 - 12 - diameter approximately equal to one quarter of the wavelength of the acoustic signals to be emitted, and the acoustic signals are beamformed to generate a diverging spherical waveform in the far-field.

[0066] In the beamforming process, the phase with which acoustic signals are emitted by each of the transmit elements 211 is controlled based on its position within the array such that the acoustic signals have the form of a diverging beam emitted from a virtual source around which the transmit elements 211 are symmetrically arranged. The transmit elements 211 closest to the corner between the surfaces of the ADAR sensor 20 are controlled to emit acoustic signals 215 with a leading phase, which combine to form an edge wave 216 extending from the ADAR sensor. The transmit elements 211 further from the corner are controlled to emit acoustic signals 214 with a lagging phase, which combine with the acoustic signals 215 in the far-field, resulting in an acoustic signal 212 with a diverging spherical waveform in the far-field.

[0067] By generating a diverging waveform in this way, the acoustic signals 212 are emitted from the ADAR sensor 50 in all directions simultaneously. The emitted signals are reflected from objects or people in the environment, and are received at the first receiver 23 and the second receiver 25. The delay between the acoustic signal 212 being emitted and the reflection being received at the first receiver and the second receiver depends on the wavelength of the acoustic signal 212, and the distance between the ADAR system 20 and the object from which the received signal is reflected. Importantly however, as the emitted signal is diverging, the reflections of the acoustic signals 212 are received at the first receiver 23 and the second receiver 25 within a narrow time window relative to the delay between the acoustic signal 212 being emitted and the reflection being received. The duration of this time window depends on the application in which the ADAR system 20 is used, but in at least some embodiments, the reflections of the acoustic signals 212 are be received at the first receiver 23 and the second receiver 25 within 100 ms. This allows the ADAR sensor 20 to perform an angular analysis based on the reflected signals received at both the first receiver 23 and the second receiver 25, rather than requiring that the emitted acoustic signals 212 be steered in different directions at different times. This allows the ADAR system 20 to achieve both low response times and a wide (i.e. >180 degree) field of view. 496.135.173120 / 01 - 13 -

[0068] The transmitter 21 of the ADAR sensor 20 of the first embodiment of the invention shown in Figures 3 to 5 comprises transmit elements 211 located on perpendicular surfaces of the ADAR sensor 20. However, in some embodiments of the invention, the ADAR sensor comprises a transmitter located at the intersection of the two surfaces, i.e. at the corner of the ADAR sensor, rather than on the surfaces themselves, as described below with reference to Figures 6 and 7.

[0069] Figure 6A shows an ADAR sensor 50 according to a second embodiment of the invention. The ADAR sensor 50 comprises a first ultrasonic receiver 53 on a first surface 530 and a second ultrasonic receiver 55 on a second surface 550, perpendicular to the first surface 530.

[0070] The ADAR sensor 50 further comprises a transmitter 51 located at the intersection of the first surface 530 and the second surface 550, i.e. at the corner between the two surfaces. The transmitter 51 comprises a single transmit element 511 , arranged to emit a diverging acoustic signal into the environment. The emitted signal is reflected from surfaces of objects or people within the environment, and is received at the first and second receivers 53 and 55, which have respective fields of view that partially overlap such that the field of view of the ADAR sensor 50 is greater than 180 degrees.

[0071] Figure 6B shows a sectional view of the transmitter 51 of the second embodiment in more detail. The transmitter 51 comprises a single transmit element 511 (e.g. a single ultrasound transducer) located at the corner of the first surface 530 and the second surface 550 of the ADAR sensor 50. The transmit element 511 generates and emits acoustic signals 512 through an outlet 513 at the corner of the ADAR sensor 50. The outlet 513 has a diameter approximately equal to one quarter of the wavelength of the acoustic signals 512, such that the acoustic signals 512 have a diverging spherical waveform in the far-field that spreads from the corner of the ADAR sensor 50. As explained above in relation to the first embodiment of the invention, this diverging signal can be received at the first receiver 53 and the second receiver 55 in a narrow time window, allowing angular analysis to be performed on the same reflected signal received at the two receivers 53, 55. 496.135.173120 / 01 - 14 -

[0072] Although the transmitter 51 shown in Figures 6A and 6B comprises a single transmit element 511 , in some embodiments the ADAR sensor comprises multiple transmit elements at the intersection between two surfaces, e.g. in cases where sufficient sound pressure cannot be generated by a single transmit element. An example of an ADAR sensor employing a transmitter comprising a plurality of transmit elements is shown in Figures 7A and 7B.

[0073] Figure 7A shows an ADAR sensor 60 according to a third embodiment of the invention. The ADAR sensor 60 comprises a first ultrasonic receiver 63 on a first surface 630 and a second ultrasonic receiver 65 on a second surface 650, perpendicular to the first surface 630. The ADAR sensor 60 further comprises a transmitter 61 comprising a plurality of transmit elements 611 located along the intersection of the first surface 630 and the second surface 650, i.e. at the corner between the two surfaces.

[0074] The transmit elements 611 emit diverging acoustic signals into the environment, which are reflected from surfaces of objects or people within the environment. The first and second ultrasonic receivers 63 and 65 receive the reflected acoustic signals, and have respective fields of view that partially overlap such that the field of view of the ADAR sensor 60 is greater than 180 degrees.

[0075] Figure 7B shows a sectional view of the transmitter 61 of the third embodiment of the invention. The transmitter 61 comprises a plurality of transmit elements 611 stacked vertically along the intersection between the first and second surfaces 630, 650 of the ADAR sensor 60, such that the transmit elements 611 are positioned along the intersection between the two surfaces in an array. The transmit elements 611 are spaced apart based on the wavelength of the acoustic signals 612 to be emitted, such that the spacing between the transmit elements 611 is approximately half of the wavelength of the acoustic signals 612.

[0076] The array of transmit elements 611 emits an acoustic signal 612 that has a diverging spherical waveform in the far-field, that spreads from the corner of the ADAR sensor. Each transmit element 611 generates and emits an acoustic signal through a respective outlet 613. The outlet 613 has a diameter approximately equal to one quarter of the wavelength of the acoustic signals to be emitted, and the 496.135.173120 / 01 - 15 - acoustic signals are beamformed to generate a diverging spherical waveform in the far-field.

[0077] In this beamforming process, the phase at which acoustic signals are emitted by each of the transmit elements 611 is controlled based on its position within the array. The transmit element 611 at the centre of the array is controlled to emit an acoustic signal 615 with a leading phase, while the transmit elements 311 at the edges of the array are controlled to emit acoustic signals 314 with a lagging phase. In the far-field, the acoustic signals 614, 615 combine, resulting in an acoustic signal 612 with a diverging spherical waveform in the far-field.

[0078] Figure 8 shows an AMR 100 comprising two ADAR sensor 200 according to an embodiment of the present invention such as any of the embodiments described above.

[0079] The ADAR sensors 200 are mounted to surfaces at the front and rear of the AMR 100 and emit acoustic signals into the environment in the vicinity of the AMR 100 and receive reflections from objects or people in environment. The received acoustic signals are sampled by a processing sensor 300 of the AMR 100 or ADAR 200 and are processed to identify the objects in the environment as explained above in relation to Figures 1 and 2. However, in contrast to the AMRs 1 and 10 shown in Figures 1 and 2, the use of two ADAR sensors 200 allows for a field of view 400 that extends 360 degrees around the AMR 100 allowing for objects to be detected at all sides of the AMR 100.

[0080] It will be appreciated by those skilled in the art that the present disclosure has been illustrated by describing one or more specific examples thereof, but is not limited to these examples; many variations and modifications are possible, within the scope of the accompanying claims.

Claims

496. 135.173120 / 01 - 16 -CLAIMS1. An acoustic detection and ranging sensor comprising: an acoustic transmitter configured to emit a diverging acoustic signal; a first acoustic receiver arranged in a first plane, configured to receive reflections of the acoustic signal from one or more surfaces in a vicinity of the sensor; and a second acoustic receiver arranged in a second plane that is nonparallel with the first plane, configured to receive the reflections of the acoustic signal; wherein the field of view of the first acoustic receiver and the field of view of the second acoustic receiver partially overlap such that the field of view of the acoustic detection and ranging sensor is greater than 180 degrees.

2. The acoustic detection and ranging sensor of claim 1 , wherein the first plane and the second plane are substantially perpendicular.

3. The acoustic detection and ranging sensor of claim 1 or 2, wherein the transmitter comprises one or more transmit elements located on the first plane and one or more transmit elements located on the second plane.

4. The acoustic detection and ranging sensor of claim 3, wherein the transmitter comprises a plurality of transmit elements arranged in an array on the first plane and a plurality of transmit elements arranged in an array on the second plane.

5. The acoustic detection and ranging sensor of claim 4, wherein the transmit elements of each array are linearly spaced.

6. The acoustic detection and ranging sensor of any of claims 3 to 5, configured to performing beamforming of acoustic signals transmitted by the transmit elements so as to construct a virtual source between them.

7. The acoustic detection and ranging sensor of claim 6, wherein performing beamforming comprises controlling the phase of acoustic signals emitted by the one or more transmit elements so as to achieve a diverging wave in the far-field.496.135.173120 / 01 - 17 -8. The acoustic detection and ranging sensor of claim 1 or 2, wherein the transmitter is located at the intersection of the first plane and the second plane.

9. The acoustic detection and ranging sensor of claim 8, wherein the transmitter comprises a plurality of transmit elements positioned along the intersection between the first plane and the second plane.

10. The acoustic detection and ranging sensor of claim 9, configured to performing beamforming of acoustic signals transmitted by the plurality of transmit elements so as to achieve a diverging wave in the far-field.

11. The acoustic detection and ranging sensor of any preceding claim, wherein the first acoustic receiver and / or the second acoustic receiver comprises an array of acoustic receive elements.

12. The acoustic detection and ranging sensor of any preceding claim, further comprising a processing system configured to: control the acoustic transmitter to cause it to emit the diverging acoustic signal; sample electrical signals output by the first and second acoustic receivers in response to the received reflections of the acoustic signal; and process the sampled electrical signals to identify the one or more surfaces in the environment.

13. The acoustic detection and ranging sensor of claim 12, wherein processing the sampled electrical signals comprises determining a range and / or a position for one or more of the surfaces.

14. The acoustic detection and ranging sensor of claim 13, wherein determining a range for each surface comprises determining a time-of-flight for the reflected acoustic signal from the respective surface.

15. A device comprising an acoustic detection and ranging sensor according to any preceding claim.496.135.173120 / 01 - 18 -16. The device of claim 15, wherein the device is an autonomous mobile robot.

17. The device of claim 15 or 16, wherein the acoustic detection and ranging sensor is provided at a first corner of the device.

18. The device of claim 17, further comprising a second acoustic detection and ranging sensor according to any of claims 1-14, wherein the second acoustic detection and ranging sensor is provided at a second corner of the device that is diagonally opposed to the first corner.

19. A method of operating an acoustic detection and ranging sensor, the method comprising: emitting a diverging signal from an acoustic transmitter; receiving reflections of the acoustic signal from one or more surfaces in a vicinity of the sensor at a first acoustic receiver arranged in a first plane; and receiving the reflections of the acoustic signal at a second acoustic receiver arranged in a second plane that is nonparallel with the first plane; wherein the field of view of the first acoustic receiver and the field of view of the second acoustic receiver partially overlap such that the field of view of the acoustic detection and ranging sensor is greater than 180 degrees.

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