Optoelectronic system for bi-directional measurement of light pulse propagation time and distance

Abstract

A system for measuring the propagation time of light pulses between at least two cells. The presented system further enables the calculation of the distance between at least two units (101a, 101b), and the successive derivative of the distance with respect to time, in different configurations. Bidirectional light time transfer between the two cells is used to calculate the propagation time of the light pulses generated by the light source of each cell.

Description

Technical Field

[0001] This invention relates to a system for measuring the propagation time of electromagnetic waves between at least two units. The presented system is also capable of calculating the distance between at least two units. Background Technology

[0002] The propagation time of an electromagnetic wave between two units and the distance between those units are related to the propagation speed of the electromagnetic wave. Therefore, these two measurements are closely related.

[0003] Systems containing active units and units that act as passive reflectors are typically used to measure the distance between two specific units. In this way, the measurement system is configured as a radar or lidar system to detect objects to be identified characterized by high reflectivity.

[0004] In radar, radio frequency is used to perform this measurement.

[0005] In radio frequency, as defined in the IEEE 802.15.4a standard, a “symmetric two-sided bidirectional ranging” method is sometimes used, characterized by sending a request through one unit and generating a response through another unit.

[0006] Furthermore, EP2602636A1 describes a method that uses radio frequency signals to identify the distance between two separate active terminals of such a frequency-modulated continuous wave radar.

[0007] The use of radio frequency (RF) signals causes several problems. First, RF (especially those with higher wavelengths) exhibits low spatial resolution, making it difficult to detect small objects or small details.

[0008] Another drawback of using radio frequency (RF) in measurements stems from the necessity of licensing its use, as RF usage is strictly regulated by government agencies in several countries. In fact, certain frequency bandwidths require specific licenses, and their inappropriate use can lead to legal issues, complicating implementation and increasing operational costs.

[0009] Alternative techniques for using radio frequency (RF) measurements include optical signals, as they offer better results in terms of accuracy, resolution, and the ability to work over longer distances.

[0010] A technical solution has been proposed that enables the calculation of the propagation time between two units using bidirectional optical time transfer, with optical components taking both the transmitted electromagnetic wave and the electromagnetic wave received by the other unit as inputs. This technical solution has been proposed in the journal article Giorgetta, FR, Swann, WC, Sinclair, LC, Baumann, E., Coddington, I., & Newbury, NR (2013) “Optical two-way time and frequency transfer over free space” (published in Nature Photonics, Vol. 7, No. 6, pp. 434-438, Springer Science and Business Media LLC) and the conference article Prochazka, I., Blazej, J., Flekova, T., & Kodet, J. (2020) “Laser-based Time Transfer through Free-space Links” (published in EPJ Web of Conferences, Vol. 243, p. 09001, edited by P. Helfenstein, EDP Sciences).

[0011] In the context of optical technology solutions, patent EP3165943A1 (claiming priority from German patent DE102015221836) describes a transmitter equipped with a communication system allowing communication between at least a first transmitting and receiving unit and a second transmitting and receiving unit, each equipped with a transmitter, a receiver, and a control unit. The first transmitting and receiving unit records the total duration dT between transmitting its own data packet and subsequently receiving a response data packet from the second transmitting and receiving unit. The second transmitting and receiving unit determines the time interval dt between receiving the data packet transmitted by the first unit and subsequently transmitting the response data packet, and transmits this time interval, recorded as information, to the first transmitting and receiving unit using the same optical channel as the packet required to transmit the measurements dT and dt. Patent EP3165943A1 further proposes the use of a device on each unit for measuring distance changes.

[0012] Specifically, the units exchange data packets using an optical free-beam communication system. As is generally accepted, an optical free-beam optical connection means that the optical signal travels directly along an unguided beam along the transmitting and receiving units. This means that there is no object like an optical fiber or waveguide guiding the optical signal along a specific path. Instead, the signal is transmitted directly in a predetermined direction in the free space between the transmitter and receiver. In this application, in practice, the transmitter and receiver should be precisely aligned so that the optical signal can travel along a predefined direction without dispersion or attenuation.

[0013] This means that these devices should be positioned so that their optical paths are unobstructed and precisely aligned. Alignment can be performed manually or using an external automated alignment system, especially in applications requiring high precision or in the presence of varying weather conditions. However, in other practical situations where the positions of the units are not constrained by the conveyor, the alignment direction cannot always be predetermined, especially over long distances or in dynamic environments where devices (e.g., drones) can move with greater degrees of freedom compared to devices restricted by a conveyor.

[0014] Furthermore, due to the large amount of information transmitted by the transmitter and receiver of the unit (which is relevant to the measurements being performed and useful for distance calculations), this technical solution presents other problems related to the high time required to assess the distance.

[0015] The transmission of large amounts of information related to measurement, and the use of the unit's transmitter and receiver for this transmission, also lead to energy inefficiency.

[0016] Therefore, identifying systems that enable more efficient distance measurement between two or more units is a technical problem.

[0017] Purpose of the invention

[0018] One object of the present invention is to provide a technical solution for calculating the propagation time of an optical pulse between at least two units. This technical solution can be used, for example, to synchronize the clocks of the two units or to calculate the distance between the two units, wherein the position of at least one of the units in space is unknown.

[0019] The present invention utilizes the high radial resolution provided by the optical frequency, which is no longer necessary for pulse transmission along previously known directions, as embodied in cited patent EP3165943A1, but rather in the space surrounding each cell.

[0020] Furthermore, the use of electromagnetic waves at optical frequencies enables the collimation of light radiation through lenses and the guidance of light beams through movable reflectors, thereby enabling the acquisition of information about the relative angular positions between units, thus enabling relative three-dimensional positioning between devices.

[0021] Furthermore, in the system of the present invention, each unit includes a communication device that allows wireless sharing of information with at least one other unit.

[0022] This invention can be applied to industrial fields, including but not limited to indoor and outdoor positioning systems, autonomous driving, triangulation, remote surgery, and clock synchronization. Summary of the Invention

[0023] The subject of this invention is a system for measuring the propagation time of an optical pulse in free space between at least two units 101.

[0024] The system of the present invention has the features of independent claim 1, the contents of which form part of this specification. Further features and embodiments of the invention are described by the following claims, the contents of which are part of this specification.

[0025] Specifically, the present invention discloses a system comprising at least two units 101, capable of evaluating the propagation time of a light pulse in the space between at least two units 101, each unit 101 comprising: a. Light source 103; b. Circuit 105, used to drive the light source 103 via an electrical signal; c. A photodetector 107 for detecting at least one light pulse generated by a light source 103 of at least one other unit 101; d. Measuring device 109 enables the analysis of two time events, which are respectively associated with the following: - Pulsating changes in electrical quantities related to light source 103; - Pulsating changes in electrical charge associated with photodetector 107; e. Processing equipment 111; f. Communication equipment 113, The feature is that each light source 103 in at least two units 101 generates at least one light pulse, and the propagation time of the light pulse in the space between the two units 101 is calculated by the processing device 111 of at least one unit 101 by processing the following data: a. The time difference between the aforementioned time events associated with a unit 101; b. The time difference between the aforementioned time events related to another unit 101 Furthermore, it is characterized in that at least one unit 101 shares information about time events analyzed by the aforementioned measuring device 109 with at least one other unit 101 via a communication device 113.

[0026] Furthermore, the present invention proposes a system characterized in that at least one processing device 111 of unit 101 processes the propagation time of the light pulse in the space between two units 101 and the propagation speed of the light pulse in the space between the units 101 to calculate the distance between the units 101.

[0027] The present invention also proposes a system in which a processing device 111 of at least one unit 101 calculates at least one of the successive derivatives of the distance between two units 101 of the system with respect to time.

[0028] One embodiment of the present invention is characterized in that the measuring device 109 of at least one unit in unit 101 includes: a. At least one time-to-digital converter 114; b. First circuit 115, used to read electrical quantities related to light source 103; c. Second circuit 116, used to read electrical quantities associated with photodetector 107.

[0029] In contrast to the preceding embodiments, another possible embodiment of the present invention is characterized in that the measuring device 109 of at least one unit in unit 101 includes: a. At least one analog-to-digital converter 117; b. First circuit 115, used to read electrical quantities related to light source 103; c. Second circuit 116, used to read electrical quantities associated with photodetector 107.

[0030] The present invention also proposes the optional use of an optical lens included in at least one unit 101 for collimating optical pulses generated by at least one unit.

[0031] The invention also proposes the optional use of a rotating reflector included in at least unit 101, which further includes an optical lens for guiding collimated light pulses to different angular positions.

[0032] An advantageous embodiment of the invention provides that the system comprises at least three units 101, and the distance between units belonging to different pairs of units 101 is processed by a geometric process to determine at least one of the following quantities: a. The location of at least one specific unit 101 in space; b. At least one of the successive derivatives of the above positions with respect to time.

[0033] The present invention also proposes a system comprising at least three units 101, wherein at least two units 101 are positioned relative to each other at a fixed and known distance and angle, thereby realizing at least one rigid subsystem, and wherein at least one of the following quantities can be calculated by a geometric procedure: a. The spatial location of at least one element 101 belonging to a rigid subsystem; b. At least one of the successive derivatives of the position of at least one element 101 belonging to a rigid subsystem in space with respect to time; c. The attitude of at least one rigid subsystem in space; d. At least one of the successive derivatives of the attitude of at least one rigid subsystem in space with respect to time.

[0034] The present invention also provides the possibility of multiple light sources 103.

[0035] The present invention also provides the possibility of multiple photodetectors 107. Attached Figure Description

[0036] The preferred embodiments are described using the accompanying drawings, wherein: [ Figure 1 [Illustrated] is a schematic representation of a system comprising two units 101 labeled 101a and 101b, wherein the light source 103 is represented by the symbol for a diode laser, the photodetector 107 by the symbol for a photodiode, and the communication device 113 by the common symbol for wireless communication.

[0037] [ Figure 2 [Illustration] is a diagram illustrating the calculation principle used to evaluate the propagation time between two units 101.

[0038] [ Figure 3 [Illustration] is a schematic diagram illustrating a unit 101 of a system according to a preferred embodiment of the present invention, which is provided for use with a time-to-digital converter 114.

[0039] [ Figure 4 [Illustration] is a schematic diagram of the input signal to a time-to-digital converter 114 having two stop inputs according to a preferred embodiment of the present invention.

[0040] [ Figure 5 [Illustration 1] is a schematic diagram of a unit 101 of a system according to another preferred embodiment of the invention, which is provided for the use of an analog-to-digital converter 117.

[0041] [ Figure 6 [Illustration] is a schematic diagram of a system that includes a rigid subsystem. Detailed Implementation

[0042] This specification provides non-limiting embodiments of the invention, such as those preferred at the time of filing the patent application. However, they are not limiting relative to other subsequently filed embodiments, and are alternatives to the preferred embodiments, although they are covered by the claims of the invention.

[0043] In the description of the preferred embodiments, for the purpose of better illustrating some embodiments, only the two units 101 denoted as numerals 101a and 101b below are considered.

[0044] Specifically, this description illustrates the invention in the case where exactly two units 101 (labeled as unit 101a and unit 101b) are present, as [ Figure 1 As shown in the diagram. However, it should be emphasized that the system also achieves the objectives of the invention when it includes more than two units 101. Each of the two units 101 under consideration includes: a. Light source 103, preferably a pulsed laser; b. Circuit 105, used to drive light source 103; c. A photodetector 107 for detecting at least one light pulse generated by a light source 103 of another of at least two units 101; d. Measuring device 109 enables the analysis of two time events, which are respectively associated with the following: i. Pulsating changes in electrical quantities related to light source 103; ii. Pulsating changes in electrical quantities associated with photodetector 107; e. Processing equipment 111; f. Communication equipment 113.

[0045] In the context of the presented embodiments, a pulsed laser is a device that uses stimulated emission through radiation to amplify light and is capable of generating photoelectromagnetic waves with a fast rise time and high peak power. They are commonly used in flash lidar, as described in the following literature: Marino, RM, Stephens, T., Hatch, RE, McLaughlin, JL, Mooney, JG, O'Brien, ME, Rowe, GS, Adams, JS, Skelly, L., Knowlton, RC, Forman, SE, & Davis, WR (2003) "A compact 3D imaging laser radar system using Geiger-mode APD arrays: system and measurements" (published in SPIE Proceedings, edited by GW Kamerman, SPIE); and Hao, Q., Tao, Y., Cao, J., & Cheng, Y. (2021) "Development of pulsed-laser three-dimensional imaging flash lidar using APD arrays" (published in Microwave and Optical Technology Letters, Vol. 63, No. 10, pp. 2492-2509, Wiley).

[0046] The system described is characterized by the following facts: a. Each light source 103 in at least two units 101 generates at least one light pulse; b. The propagation time of the light pulse in the space between the two units 101 is calculated by the processing device 111 of at least one unit by processing the following data: i. The time difference between the aforementioned time events associated with a unit 101; ii. The time difference between the aforementioned time events related to another unit 101; c. At least one unit 101 shares information about time events analyzed by the aforementioned measuring device 109 with at least one other unit 101 via communication device 113.

[0047] Therefore, each light source 103 driven by the corresponding circuit 105 can generate a light pulse capable of propagating within a sufficiently large solid angle in the space surrounding the unit, such that the light pulse generated by each unit can reach other units, even when the relative direction between two units is unknown. To achieve this, it is clear that the light pulse should preferably be divergent rather than collimated.

[0048] The system described in this patent application overcomes the technical problems of the prior art by using the same light pulses in a space not limited to a single dimension, particularly the previously cited patent EP3165943A1. This is because an expert in the art familiar with patent EP3165943A1, in the unlikely scenario of attempting to extend the application of patent EP3165943A1, would clearly use common-sense techniques capable of modifying the divergence of the light signal, such as using a diverging lens. However, this technical solution will result in low efficiency in terms of measurement speed and power consumption, primarily due to the fact that in patent EP3165943A1, the same light emitter is used both to transmit light pulses useful for measuring time differences and to transmit optical information useful for calculating optical distances. In practice, under this assumption, a high-power light emitter would be necessary to radiate over a wide solid angle, and such a high-power light emitter typically has a much lower pulse rate compared to a low-power light emitter.

[0049] In contrast, the present invention: a. It does not necessarily assume a preferred direction for the emission of the optical signal, and even sending a single optical pulse can play a role in achieving power reduction; b. A communication device 113 is used, which is dedicated to sharing the information required to calculate the propagation time. Therefore, the information is not shared between the light source 103 and the photodetector 107, thereby reducing the signal transmitted between them. The presence of the communication device 113, separate from the light source 103 and the photodetector 107, allows for both faster transmission and reception of light pulses by the light source 103 and the photodetector 107, and improved energy efficiency, thus enabling faster and more energy-efficient measurements. It is clear that the communication device 113 is not limited to using optical signals; rather, it is more energy efficient from an energy perspective when utilizing signals in different bandwidths (e.g., signals commonly used for transmitting data in a local area network, such as Bluetooth® or Wi-Fi®), because the signal is transmitted using a different channel than that used by the light source 103.

[0050] Each unit 101 is also provided with a photodetector 107, which detects light pulses from another light source 103. Specifically, unit 101a uses the photodetector 107 to detect at least one light pulse generated by the light source 103 of unit 101b, while unit 101b uses the photodetector 107 to detect at least one light pulse generated by the light source 103 of unit 101a.

[0051] According to a preferred embodiment of the invention, in the provided embodiment, the processing device 111 of each unit sends a start signal to the circuit 105 driving the pulsed laser. Therefore, the circuit 105 of each unit 101 drives the pulsed laser, causing it to generate optical pulses. The optical pulses generated by the pulsed laser of each unit 101 propagate through the three-dimensional space surrounding each of the two units 101 and reach the other unit 101.

[0052] According to a preferred embodiment, it is assumed that the light pulse generated by the light source 103 is synchronized with the pulsed change of an electrical quantity, which is the current flowing through the light source 103. The photodetector 107 of each unit detects the light pulse from another unit 101. According to a preferred embodiment, the detection event of the light pulse causes a pulsed change in the electrical quantity of the photodetector 107 (which is the current generated by the photodetector 107), and this pulsed change is considered to be synchronized with the light pulse.

[0053] The measuring device 109, connected to both the light source 103 and the photodetector 107, enables the identification of two events, one associated with a pulsed change in the current flowing through the light source 103 and the other with a pulsed change in the current generated by the photodetector 107. Further details relating to the measuring device 109 in a preferred embodiment of the invention will be described later.

[0054] The processing device 111 is also connected to the measuring device 109 and the communication device 113. The processing device 111 of unit 101a communicates wirelessly with the processing device 111 of unit 101b.

[0055] According to a preferred embodiment of the present invention, the communication device 113 of each unit includes a radio frequency antenna.

[0056] The processing device 111 of at least one of the two units 101 (e.g., unit 101b) transmits information related to the time difference between two events identified by the measuring device 109 to the processing device 111 of the other unit 101 (in this case, unit 101a) via the communication device 113. The processing device 111 of the other unit 101 (in this case, unit 101a) receives the information related to the time difference between the events identified by unit 101b via the communication device 113. The processing device 111 of unit 101a calculates the propagation time of the light pulse between the two units 101a and 101b as half the absolute value of the sum of the following: a. The time difference between two events identified by unit 101a; b. The time difference between two events identified by unit 101b.

[0057] It was observed that the time difference between two events associated with unit 101a and between two events associated with unit 101b can have opposite signs.

[0058] To clarify the operational principle of this method, [ Figure 2 ]. [ Figure 2 [This is a diagram illustrating the principle of propagation time calculation. Specifically, it shows the optical pulses generated and received by each unit 101. More details are provided in [...] Figure 2 The diagram shows a first graph and a second graph. The first graph at the top corresponds to unit 101a, and the second graph at the bottom corresponds to unit 101b. The vertical axis of each unit 101 represents an electrical quantity labeled "I," which is current in the preferred embodiment, and the horizontal axis of each unit 101 represents a time axis labeled "t." For understanding the operating principle, both units 101 are considered to share a common time axis. However, it will be shown that clock synchronization between the two units 101 is not required.

[0059] The solid line 207 of the first graph shows the current flowing through the light source 103 (e.g., a pulsed laser) of unit 101a. The dashed line 208 of the first graph shows the current generated by the photodetector of unit 101a. The solid line 209 of the second graph shows the current flowing through the light source 103 of unit 101b. The dashed line 210 of the second graph shows the current generated by the photodetector of unit 101b.

[0060] In the first graph, the moment when the pulse-like change in the current flowing through the light source 103 in unit 101a occurs is marked as t. AL And the moment when the pulsed change in current generated by the photodetector 107 of unit 101a occurs is marked as t. AR In this exemplary description, t ALand t AR Identify the peaks of the curves they involve.

[0061] In the second graph, the moment when the pulsed change in the current flowing through the light source 103 in unit 101b occurs is marked as t. BL And the moment when the pulse change of the current generated by the photodetector 107 of unit 101b occurs is marked as t. BR Specifically, in this exemplary description, t BL and t BR Identify the peak values ​​of the electrical quantities involved.

[0062] In the first graph, the equal propagation times from unit 101a to unit 101b and from unit 101b to unit 101a are denoted as t. p .

[0063] By examining this graph, we can write: [Mathematical Expression 1]

[0064] It should be noted that the quantity (t) AL -t AR ) and (t BL -t BR It can take both positive and negative values. It should also be noted that when it is previously unknown which unit 101 generated the first pulse, the absolute value is necessary. Due to the amplitude (t... AL -t AR The amplitude (t) can be measured by unit 101a, and the amplitude (t) BL -t BR The propagation time can be measured by unit 101b, therefore the clocks of the two units 101 do not need to be synchronized. The propagation time is calculated as follows: [Mathematical Expression 2]

[0065] Alternatively, an equivalent formula may be used. Advantageously, at least one processing device 111 of unit 101 can process the propagation time of the light pulse in the space between the two units 101 and the propagation speed of the light pulse in the space between the units 101 to calculate the distance between the units 101.

[0066] Therefore, the distance between the two units 101 can be further calculated by multiplying the propagation time by the propagation speed.

[0067] Furthermore, advantageously, at least one of the processing devices 111 of unit 101 can calculate at least one of the successive derivatives of the distance between two units 101 of the system with respect to time, such as velocity and acceleration, which can be calculated from information about the distance.

[0068] Several preferred embodiments will be provided in detail below.

[0069] Implementation using time-to-digital converter 114

[0070] In the following description, embodiments of the invention will be described in more detail, with further details provided regarding the measurement processing and measuring device 109 present in each unit 101.

[0071] According to a preferred embodiment of the present invention, [ Figure 3 A schematic diagram of a general unit 101 of the two units 101 of the system of the present invention is provided, wherein the unit 101 includes: -Light source 103, such as a pulsed laser; -Circuit 105 is used to drive light source 103; - Photodetector 107; - Measuring device 109, comprising the following: a. A time-to-digital converter 114 having at least two stop inputs; b. First circuit 115, used to read electrical quantities related to light source 103; c. Second circuit 116, used to read electrical quantities associated with photodetector 107.

[0072] -Processing equipment 111; - Communication equipment 113.

[0073] It should be noted that the time-to-digital converter 114 is a digital measuring instrument used to measure the time intervals between various events. These time intervals are identified by a start signal and at least one stop signal present at the input of the time-to-digital converter 114.

[0074] Here, the operation of each unit 101 is shown in the described preferred embodiment. In the described embodiment, the first circuit 115 for reading out the pulsed laser or general light source 103 is characterized in that it enables the current flowing through the pulsed laser to be converted into a voltage proportional to it, and the voltage to be compared with a reference voltage. In a preferred non-limiting embodiment, the first circuit 115 for reading out the pulsed laser is implemented using a resistor connected in series with the pulsed laser and placed between the pulsed laser and a ground node, the comparator comparing the voltage at the common node between the resistor and the pulsed laser with a threshold voltage.

[0075] In the described preferred embodiment, the second circuit 116 for reading out the photodetector 107 is characterized in that it enables the current generated by the photodetector 107 to be converted into a voltage proportional to it and the voltage to be compared with a threshold voltage value. In the described embodiment, the second circuit 116 for reading out the photodetector is implemented in a non-limiting manner using a transimpedance amplifier connected to the photodetector 107 and a comparator connected to the output of the transimpedance amplifier.

[0076] According to a preferred embodiment of the invention, the time-to-digital converter 114 has at least one start input and at least two stop inputs. A processing device 111 is connected to one start input of the time-to-digital converter 114. The output of a first circuit for reading out the pulsed laser is connected to the stop input of the time-to-digital converter 114. The output of a second circuit for reading out the photodetector 107 is connected to the other stop input of the time-to-digital converter 114. At least one output of the time-to-digital converter 114 is connected to the processing device 111 to transmit the result of a digital time measurement.

[0077] In the preferred embodiment described in this invention, the processing device 111 in each unit 101 sends a start signal to the start input of the time-to-digital converter 114, which initiates the time-to-digital conversion process. A digital signal delayed relative to the start signal is sent by the processing device 111 of each unit 101 to a circuit 105 for driving the light source 103, and the circuit 105 for driving the light source 103 thus generates a current to drive the light source 103 (i.e., in this embodiment, a pulsed laser).

[0078] When a current pulse flows through the pulsed laser, a first circuit 115 for reading out the pulsed laser generates a stop signal at the first stop input of the time-to-digital converter 114, synchronously with the optical pulse generated by the pulsed laser.

[0079] When the light pulse is received by the photodetector 107 of each unit 101, the second circuit 116 for reading out the photodetector 107 generates a stop signal at the second stop input of the time-to-digital converter 114 of each unit 101.

[0080] To better illustrate the operation of the preferred embodiments of the described invention, see also [ Figure 4 The figure shows two graphs, one at the top and one at the bottom, relating to cell 101a. In each graph, the vertical axis represents voltage (labeled "V") and the horizontal axis represents time (labeled "t").

[0081] Specifically, [ Figure 4Each of these two graphs shows: - The voltage at the start inputs 403 and 404 of the time-to-digital converter 114 of each unit 101; - The start time (start A, start B) of the time-to-digital converter 114 of units 101a and 101b. - The voltage at the first stop inputs 405, 406 of the time-to-digital converter 114 of each unit 101; - The stop time (stop LA, stop LB) corresponding to the first stop input of the time-to-digital converter 114 - The voltage at the second stop inputs 407, 408 of the time-to-digital converter 114 in each unit; - The stop time (stop RA, stop RB) corresponding to the second stop input of the time-to-digital converter 114.

[0082] Once the processing device 111 of unit 101a connected to the corresponding time-to-digital converter 114 reads the stop time measurement values ​​(stop LA, stop RA) and the processing device 111 of unit 101b connected to the corresponding time-to-digital converter 114 reads the stop time measurement values ​​(stop LB, stop RB), the processing device 111 of unit 101b transmits the measurement values ​​(stop LB – stop RB) to the processing device 111 of unit 101a via the communication device 113 of unit 101b, and the processing device 111 of unit 101a receives this communication via the communication device 113 of unit 101a, and calculates the propagation time tp as: [Mathematical Expression 3]

[0083] In the preferred embodiment described in this invention, the communication device 113 of each unit 101 is a radio frequency antenna. Obviously, in different preferred embodiments, such communication device 113 may also include a computing unit separate from the processing device 111 of the corresponding unit 101.

[0084] According to a preferred embodiment, the measurement process initiated by sending a start signal from the processing device 111 of each unit to the time-to-digital converter 114 of each unit 101 is periodically repeated by the processing device 111 of each unit 101 to acquire several measurement values ​​to calculate statistical parameters, such as mean and variance. In this case, each unit 101 generates and detects a sequence of light pulses.

[0085] In a further preferred, non-limiting embodiment of the invention, two time-to-digital converters can be used in each unit 101 instead of a single time-to-digital converter 114 with two stop inputs. In this case, in the described embodiment, both converters receive the same start signal from the processing device 111.

[0086] The embodiments described above do not limit the implementation of the system subject matter of the present invention. For example, in different embodiments of the present invention, the start signal (start A, start B) in each unit 101 may be generated internally by the time-to-digital converter 114, and a signal delayed relative to the start signal may be generated by the time-to-digital converter 114 and sent to the circuit 105 driving the light source 103.

[0087] Implementation using analog-to-digital converter 117

[0088] [ Figure 5 The diagram schematically illustrates each of the two units 101 (unit 101a and unit 101b) of the system according to a preferred embodiment of the invention, thereby providing details of the measuring device 109 with respect to each unit 101.

[0089] Specifically, each unit 101 includes: - A pulsed laser, which is the light source 103; -Circuit 105 is used to drive a pulsed laser; - Photodetector 107; - Measuring device 109, comprising the following: a. An analog-to-digital converter 117 having at least two input channels; b. First circuit 115, used to read electrical quantities related to the pulsed laser; c. Second circuit 116, used to read electrical quantities associated with photodetector 107.

[0090] -Processing equipment 111; - Communication equipment 113.

[0091] The operation of each unit 101 according to the described embodiment is shown below.

[0092] In a preferred embodiment of the invention described herein, the first circuit 115 for reading out a pulsed laser is characterized in that it enables the conversion of the current flowing through the pulsed laser into a voltage proportional to it. In a preferred, non-limiting embodiment, the first circuit 115 for reading out the pulsed laser utilizes a resistor connected in series with the pulsed laser, located between the pulsed laser and a ground node, and the voltage amplifier amplifies the voltage across the resistor.

[0093] In the described embodiment, the second circuit 116 for reading out the photodetector 107 is characterized in that it enables the conversion of the current generated by the photodetector 107 into a voltage proportional to it. In the described embodiment, the second circuit 116 is provided in a non-limiting manner with a transimpedance amplifier whose input is connected to the detector.

[0094] The processing device 111 of each unit 101 starts the measurement using a start signal sent to the circuit 105 that drives the pulsed laser.

[0095] The two input channels of the analog-to-digital converter 117 enable sampling and digital conversion of the voltage at the output of the first circuit 115 used for reading out the pulsed laser and the voltage at the output of the second circuit 116 used for reading out the photodetector 107. In this embodiment, the analog-to-digital converter 117 connected to the processing device 111 provides the processing device 111 with data generated from the digitization of the input signals.

[0096] In order to measure the time difference between the arrival time of a pulse measured by one channel of analog-to-digital converter 117 and the arrival time of a pulse measured by another channel of analog-to-digital converter 117, processing device 111 uses known processing techniques, such as cross-correlation between two digitized signals, or evaluating the arrival time of each pulse converted into digital data using a digital threshold.

[0097] The processing device 111 of one unit 101 (e.g., 101b) transmits the time difference between identified events to the processing device 111 of another unit 101 (e.g., 101a) via the communication device 113 of each unit 101. The processing device 111 of unit 101a calculates the propagation time as half the absolute value of the sum of the following: a. The time difference between events identified by unit 101a; b. The time difference between events identified by unit 101b.

[0098] Implementation including optical lenses and optionally rotating mirrors

[0099] In another embodiment, at least one unit 101 includes an optical lens for collimating the light pulses generated by the light source 103, and optionally, a rotating mirror for guiding the collimated beam to different angular positions relative to a predefined reference frame fixed to the unit 101.

[0100] Therefore, according to this embodiment, in the operation configuration of at least one unit 101 described above, the rotating mirror is used to sequentially guide the optical pulses collimated by the optical lens to different directions in the three-dimensional space that can be explored by the rotating mirror itself.

[0101] Therefore, distance measurement can only occur when the collimating beam of one of the units 101a is oriented in a direction that is approximately parallel to the direction that connects the unit 101a to another unit 101b by means of the movement achieved by the rotating mirror, and the distance and orientation of the other unit relative to the unit 101a need to be known.

[0102] When the collimated light pulse of unit 101a is guided in a direction approximately parallel to the direction between unit 101a and unit 101b, the latter is able to receive the collimated light pulse emitted by another unit 101a and send information about the measurement of the time difference taken to the same unit 101a.

[0103] The processing device 111 is thus able to obtain information related to the relative angular attitude of another unit 101b by knowing the angular position adopted by the rotating reflector during measurement.

[0104] Implementation methods provided for multiple sources or detectors

[0105] When a unit 101 is provided with a single light source 103 and / or a single photodetector 107, the unit 101 cannot send light pulses to and / or receive light pulses from all angular directions in the surrounding space. Therefore, in this case, it is advantageous to provide the same unit 101 with more than one light source 103 and / or more than one photodetector 107, so that the transmitted and / or received light pulses can cover a wider solid angle.

[0106] This enables the reliability of the system, which is the subject of this invention, to be increased through redundancy, and maximizes the field of view in terms of solid angle.

[0107] The aforementioned multiple light sources 103 can be driven by circuits 105 in unit 101 as if they were a single light source 103, or have multiple different circuits 105 operating simultaneously.

[0108] Alternatively, each photodetector 107 may be connected to the same measuring device 109, which will identify the first received pulse from one of the photodetectors belonging to the same unit 101. In the absence of overlapping fields of view of the photodetectors 107, only one photodetector of the photodetectors 107 will identify the pulse from the other unit 101.

[0109] Methods for implementing triangulation or trilateration

[0110] According to an embodiment of the subject matter of claim 8, the distances obtained between at least three different units 101 can be used in geometric and topological processes (such as triangulation or trilateration) to know the location of one of the aforementioned units 101 and further topological information of the system composed of the different units 101.

[0111] As an example, in a particularly advantageous implementation, the system consists of four units 101, three of which are fixed and one unit 101 is movable in a two-dimensional space, such that the distance measured between the movable unit 101 and each of the fixed units 101 can uniquely identify the position of the movable unit 101 in the two-dimensional space.

[0112] In detail, it should be noted that three units are sufficient if only the moving unit moves in one-dimensional space; for this purpose, one moving unit and two fixed units in one-dimensional space are necessary.

[0113] Similarly, if the movable unit can move in a two-dimensional space, then four units (three of which are fixed and one is movable) are necessary, while in a three-dimensional space, five units (four of which are fixed and one is movable) are necessary.

[0114] Implementation methods for detecting different degrees of freedom of a rigid subsystem

[0115] According to one embodiment of the invention, and based on the subject matter of claim 9, some units 101 of the system subject matter of the invention are positioned relative to each other at a fixed distance and angle to realize at least one rigid subsystem, i.e., a subsystem in which at least two units 101 have a fixed distance and orientation from each other. In this way, knowledge of the distance between each of the aforementioned units 101 belonging to the rigid subsystem and at least one unit 101 not belonging to the aforementioned subsystem, as well as knowledge of the relative positions of the units 101 belonging to the rigid subsystem, makes it possible to detect the translational and rotational degrees of freedom of the aforementioned rigid subsystem relative to the at least one unit 101 not belonging to the aforementioned subsystem.

[0116] In practice, since the relative positions of the units 101 implementing the rigid subsystem are known, when a unit 101 that does not belong to the rigid subsystem identifies, for example, its distance to each of the two units 101 that belong to the subsystem, the attitude of the rigid subsystem can be inferred from the aforementioned distance, even if the rigid subsystem has only one rotational degree of freedom and no translational degree of freedom. In the case where there are two units 101 that do not belong to the rigid subsystem, and the rigid subsystem has only one translational degree of freedom, the position of the rigid subsystem relative to the two units 101 that do not belong to the subsystem can be inferred.

[0117] In the presence of more elements 101 belonging to the rigid subsystem and / or more elements 101 not belonging to the subsystem, it is possible to infer more rotational and / or translational degrees of freedom of the rigid subsystem relative to at least one element 101 not belonging to the rigid subsystem.

[0118] For example, a rigid subsystem can be rigidly connected to a moving body, for which it is necessary to know its position and orientation in space during time evolution.

[0119] For illustrative purposes, [ Figure 6 The diagram illustrates a system comprising five units 101a, 101b, 101c, 101d, and 101e, which includes a rigid subsystem consisting of four units 101a, 101b, 101c, and 101d. The relative positions of the four units 101a, 101b, 101c, and 101d are known within this rigid subsystem. Unit 101e is not part of the rigid subsystem.

[0120] In a preferred embodiment, units 101a, 101b, 101c, and 101d belonging to the rigid subsystem are activated sequentially (meaning they send light pulses), while unit 101e is always activated.

Claims

1. A system comprising at least two units (101) capable of evaluating the propagation time of an optical pulse in the space between at least two of the units (101), each unit (101) comprising: a. Light source (103); b. Circuit (105) for driving the light source (103) by an electrical signal; c. A photodetector (107) for detecting at least one light pulse generated by the light source (103) of at least one other unit (101); d. A measuring device (109) that enables the analysis of two time events, each associated with one of the following: i. Pulsating changes in electrical quantities associated with the light source (103); ii. Pulsed changes in electrical quantities associated with the photodetector (107); e. Processing equipment (111); f. Communication equipment (113); The feature is that each of the light sources (103) in at least two units (101) generates at least one light pulse, and the propagation time of the light pulse in the space between the two units (101) is calculated by the processing device (111) of at least one unit (101) by processing the following data: a. The time difference between the time events associated with a unit (101); b. The time difference between the time events associated with another unit (101); Furthermore, it is characterized in that at least one unit (101) shares information about the time event analyzed by the measuring device (109) with at least another unit (101) via the communication device (113).

2. The system according to claim 1, further characterized in that, The processing device (111) of at least one unit (101) processes the propagation time of the light pulse in the space between the two units (101) and the propagation speed of the light pulse in the space between the units (101) to calculate the distance between the units (101).

3. The system according to claim 2, further characterized in that, The processing device (111) of at least one unit (101) calculates at least one of the successive derivatives of the distance between two units (101) of the system with respect to time.

4. The system according to any one of the preceding claims, characterized in that, The measuring device (109) of at least one of the units (101) includes: a. At least one time-to-digital converter (114). b. A first circuit (115) for reading electrical quantities related to the light source (103); c. A second circuit (116) for reading electrical quantities associated with the photodetector (107).

5. The system according to any one of claims 1 and 3, wherein, The measuring device (109) of at least one unit (101) includes: a. At least one analog-to-digital converter (117); b. A first circuit (115) for reading electrical quantities related to the light source (103); c. A second circuit (116) for reading electrical quantities associated with the photodetector (107).

6. The system according to any one of the preceding claims, characterized in that, At least one unit (101) further includes an optical lens for collimating the light pulses generated by the light source (103).

7. The system according to claim 6, characterized in that, At least one unit (101) further includes a rotating mirror for guiding collimated light pulses according to different angular positions.

8. The system according to claim 2, comprising at least three units (101), wherein, The distance between elements (101) belonging to different element (101) pairs is processed through a geometric process to determine at least one of the following quantities: a. The location of at least one specific unit (101) in space; b. At least one of the successive derivatives of the position with respect to time.

9. The system according to claim 2, comprising at least three units (101), wherein, At least two units (101) are positioned relative to each other at a fixed and known distance and angle to realize a rigid subsystem, wherein at least one of the following quantities can be calculated by a geometric process: a. The spatial position of at least one element (101) belonging to a rigid subsystem; b. The position of at least one element (101) belonging to a rigid subsystem in space relative to the successive derivatives of time; c. The attitude of at least one rigid subsystem in space; d. At least one of the successive derivatives of the attitude of at least one rigid subsystem in space with respect to time.

10. The system according to any one of the preceding claims, characterized in that, Each unit (101) includes multiple light sources (103).

11. The system according to any one of the preceding claims, characterized in that, Each unit (101) includes multiple photodetectors (107).

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