Optoelectronic system for bidirectional measurement of light pulse propagation time and distance

Abstract

This provides a solution for calculating the propagation time of an optical pulse between at least two units. [Solution] A system for measuring the propagation time of light pulses between at least two units. The system further enables the calculation of the distance between at least two units (101a, 101b) and the continuous derivative of said distance with respect to time in various configurations. Bidirectional optical time transfer between the two units is used to calculate the propagation time of light pulses generated by the light source of each unit.

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 also enables the calculation of the distance between at least two units. [Background technology]

[0002] The propagation time of electromagnetic waves between two units and the distance between units are linked by the propagation speed of electromagnetic waves. Therefore, the two measurements are closely related.

[0003] A system comprising an active unit and a passive reflector unit has traditionally been used to measure the distance between two specific units. In this way, the measuring system is configured as a radar or lidar that detects the object to be identified, characterized by high reflectivity.

[0004] In radar, such measurements are performed using radio frequencies.

[0005] In radio frequencies, the "symmetric bidirectional ranging" method may be used, as defined in the IEEE 802.15.4a standard, which is characterized by transmitting a request by one unit and generating a response by another unit.

[0006] Furthermore, European Patent Application Publication No. 2602636 describes a method for determining the distance between two independent active terminals, such as frequency-modulated continuous-wave radar, using radio frequency signals.

[0007] The use of high-frequency signals presents several problems. First, radio frequencies, especially those with high wavelengths, have low spatial resolution, making it difficult to detect small objects or fine details.

[0008] Another drawback of measurements using radio frequencies is that their use is strictly regulated by government authorities in multiple countries, requiring permits for their use. In fact, certain frequency bands require special licenses, and their use may be inappropriate and lead to legal problems, complicating implementation and increasing operational costs.

[0009] As an alternative to using radio frequencies for measurement, optical signals can be used because they offer superior results in terms of accuracy, resolution, and long-range operability.

[0010] A solution has been proposed that utilizes bidirectional optical time transmission and uses an optical component that takes both the transmitted electromagnetic wave and the electromagnetic wave received by the other unit as input to calculate the propagation time between two units. These solutions have been published in the academic journal article Giorgetta, FR, Swann, WC, Sinclair, LC, Baumann, E., Coddington, I., Newbury, NR, "Bidirectional Optical Time-Frequency Transmission over Free Space," *Nature Photonics*, Vol. 7, No. 6, pp. 434-438, Springer Science and Business Media LLC, 2013, and in the conference paper Prochazka, I., Blazej, J., Flekova, T., Kodet, J., "Laser-Based Time Transmission over Free-Space Link," in P. Helfenstein (ed.), *EPJ Web of Conferences*, Vol. 243, p. 09001, EDP Sciences, 2020.

[0011] In the realm of optical solutions, European Patent Application No. 3165943 (claiming priority to German Patent No. 102015221836) describes a conveyor equipped with a communication system enabling communication between at least a first transceiver unit and a second transceiver unit, wherein each unit comprises a transmitter, a receiver, and a control unit. The first transceiver unit records the total time interval dT between a data packet it transmits and a response data packet received from the second transceiver unit. The second transceiver unit measures the time interval dt from the reception of a data package transmitted from the first unit to the subsequent transmission of a response data package, records this measured time interval as information, and transmits it to the first transceiver unit using the same optical channel used to transmit dT and the packages necessary for measuring dt. European Patent Application No. 3165943 further proposes installing a device for measuring changes in distance in each unit.

[0012] Specifically, the units exchange data packages using an optical free-beam communication system. Optical free-beam connection, as commonly understood, means that optical signals propagate directly between a transmitting unit and a receiving unit as a non-guided beam. This means that objects such as optical fibers or waveguides do not guide the optical signals along a specific path. Instead, the signal is transmitted directly in a predetermined direction in the free space between the transmitter and receiver. In such applications, the transmitter and receiver must be precisely positioned so that the optical signal can propagate along the predetermined direction without dispersion or attenuation. [Overview of the project] [Problems that the invention aims to solve]

[0013] This means that the devices should be positioned so that the optical paths between them are precisely aligned without obstructions. Alignment can be done manually or using an external automatic alignment system, which is particularly effective in applications requiring high precision or under fluctuating weather conditions. However, in other practical situations where the position between units is not constrained by a conveyor, especially over long distances or in dynamic environments, it is not always possible to predetermine the alignment direction when devices such as drones move with a greater degree of freedom than that constrained by a conveyor.

[0014] Furthermore, this type of solution presents another problem: the amount of information transmitted using the unit's transmitter and receiver is enormous, and since this information is related to measurements and useful for distance calculations, the time required for distance evaluation is long.

[0015] Transmitting large amounts of information related to measurements, and using the unit's transmitter and receiver for that transmission, also leads to reduced energy efficiency.

[0016] Therefore, the technical challenge is to identify a system that can more efficiently measure the distance between two or more units.

[0017] One object of the present invention is to provide a solution for calculating the propagation time of an optical pulse between at least two units, which is useful, for example, for synchronizing the clocks of two units or for calculating the distance between two units when the spatial position of at least one of the units is unknown.

[0018] The present invention leverages the high radial resolution provided by optical frequencies and uses optical frequencies to transmit pulses within the space surrounding each unit, not necessarily along a previously known direction, as done in cited European Patent Application No. 3165943.

[0019] Furthermore, by using electromagnetic waves in the optical frequency band, it becomes possible to collimate light emission using a lens and direct the light beam using a movable mirror. This also makes it possible to obtain information on the relative angular position between units, and realizes relative three-dimensional positioning between devices.

[0020] Furthermore, in the system of the present invention, each unit includes a communication device capable of wirelessly sharing information with at least one other unit.

[0021] The present invention can be applied to, but not limited to, industrial fields including indoor and outdoor positioning systems, autonomous driving, triangulation, remote surgery, and clock synchronization. [Means for Solving the Problems]

[0022] The subject of the present invention is a system for measuring the propagation time of light pulses in free space between at least one unit 101.

[0023] The system of the present invention has the features of independent claim 1, the content of which forms part of the present specification. Further features and embodiments of the present invention are described by the following claims, the content of which forms part of the present specification.

[0024] In particular, the present invention is a system comprising at least two units 101 and capable of evaluating the propagation time of light pulses in the space between the at least two units 101, wherein each unit 101:[ a. a light source 103, b. an electric circuit 105 that drives the light source 103 by an electric signal, c. a photodetector 107 that detects 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 analysis of two temporal events, e. a processing device 111, f. a communication device 113 and wherein each of said events is - Sudden changes in the amount of electricity related to the light source 103, - This is related to a sudden change in the amount of electricity associated with the photodetector 107, 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 controlled by the processing unit 111 of at least one unit 101. a. The time difference between temporal events related to one unit 101, b. The time difference between temporal events related to another unit 101, The system is disclosed in which data is processed to calculate, and at least one unit 101 shares information about temporal events analyzed by the measuring device 109 with at least one other unit 101 via a communication device 113.

[0025] Furthermore, the present invention proposes a system in which a processing unit 111 of at least one unit 101 processes the propagation time of an optical pulse in the space between two units 101 and the propagation speed of an optical pulse in the space between units 101, and calculates the distance between the units 101.

[0026] The present invention further proposes a system in which a processing unit 111 of at least one unit 101 calculates at least one time-sequential derivative of the distance between two units 101 in the system.

[0027] One embodiment of the present invention provides a measuring device 109 comprising at least one unit 101, a. At least one time-to-digital converter 114, b. A first electrical circuit 115 for reading the amount of electricity related to the light source 103, c. A second electrical circuit 116 for reading the electrical quantity related to the photodetector 107, It is characterized by including.

[0028] A possible further embodiment of the present invention, in addition to the foregoing, is a measuring device 109 of at least one unit 101, a. At least one analog-to-digital converter 117, b. A first electrical circuit 115 for reading the amount of electricity related to the light source 103, c. A second electrical circuit 116 for reading the electrical quantity related to the photodetector 107, It is characterized by including.

[0029] The present invention further proposes the optional use of optical lenses contained within at least one unit 101 to parallelize light pulses generated by at least one unit.

[0030] The present invention further proposes the use of any rotating mirror included in at least unit 101, which further comprises optical lenses, to direct parallelized light pulses to different angular positions.

[0031] An advantageous embodiment of the present invention comprises a system having at least three units 101, wherein the distance between the units 101 belonging to different pairs is processed by geometric processing, a. The position of at least one specific unit 101 in space, b. At least one of the continuous derivatives with respect to time with respect to the above position, This provides a way to determine at least one of the quantities.

[0032] The present invention comprises at least three units 101, where at least two units 101 are arranged relative to each other at a fixed and known distance and angle to realize at least one rigid subsystem, and by a geometric procedure, a. The spatial position of at least one unit 101 belonging to one rigid subsystem, b. At least one continuous derivative with respect to time with respect to the spatial position of at least one unit 101 belonging to at least one rigid subsystem, c. the spatial orientation of at least one rigid subsystem, and d. at least one continuous derivative with respect to time with respect to the spatial orientation of at least one rigid subsystem, We further propose a system that can calculate at least one of the quantities.

[0033] The present invention also offers the possibility of multiple light sources 103.

[0034] The present invention also offers the possibility of multiple photodetectors 107. [Brief explanation of the drawing]

[0035] Preferred embodiments will be described with reference to the drawings accompanying this specification.

[0036] [Figure 1] Figure 1 is a schematic diagram of a system consisting of two units 101 labeled 101a and 101b, where the light source 103 is represented by the symbol for a diode laser, the photodetector 107 is represented by the symbol for a photodiode, and the communication device 113 is shown by the general symbol for wireless communication. [Figure 2] Figure 2 illustrates the computational principle used to evaluate the propagation time between two units 101. [Figure 3] Figure 3 is a schematic diagram showing a unit 101 of a system that provides the use of a time-to-digital converter 114 in a preferred embodiment. [Figure 4] Figure 4 is a schematic diagram showing the input signals to a time-to-digital converter 114 having two stop inputs in a preferred embodiment. [Figure 5] Figure 5 is a schematic diagram showing a unit 101 of a system that provides the use of an analog-to-digital converter 117 in a preferred embodiment. [Figure 6] Figure 6 is a schematic diagram of the system including the stiffness subsystem. [Modes for carrying out the invention]

[0037] This specification provides non-limiting examples of embodiments of the invention that were considered preferred at the time of filing the patent application. However, these do not limit other post-filing embodiments that are included in the claims of the invention but replace the preferred embodiments.

[0038] In describing preferred embodiments, to clarify some examples, we will consider only two units 101, shown below as numbers 101a and 101b.

[0039] In particular, this specification illustrates the invention in the case where there are exactly two units 101, labeled as unit 101a and unit 101b, as shown in Figure 1. However, it is emphasized that the objective of the invention can be achieved even when the system includes two or more units 101. Each of the two units 101 considered is: a. Light source 103, preferably a pulsed laser, b. An electrical circuit 105 that drives the light source 103, c. A photodetector 107 that detects at least one light pulse generated by at least one of the two light sources 103 of the two units 101, d. Each, i. Sudden changes in the amount of electricity related to the light source 103, ii. Sudden changes in the electrical quantity related to the photodetector 107, e. Processing device 11, f. Includes a measuring device 109 that enables the analysis of two temporal events related to the communication device 113.

[0040] In the field of the presented example, pulsed lasers are devices that use optical amplification by the stimulating emission of radiation, which can generate optical electromagnetic waves with rapid rise times and high peak power. These are often used in flash LiDAR, as described in the papers 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, "A compact 3D imaging laser radar system using a Geiger-mode APD array: System and measurements," in GW Kamerman (ed.), *SPIE Proceedings*, SPIE, 2003, and Hao, Q., Tao, Y., Cao, J., Cheng, Y., "Development of pulsed laser three-dimensional imaging flash LiDAR using an APD array," *Microwave and Optical Technology Letters*, Vol. 63, No. 10, pp. 2492-2509, Wiley, 2021.

[0041] The system described is a. The fact that each light source 103 in at least two units 101 generates at least one light pulse, b. The propagation time of the optical pulse in the space between the two units 101 is determined by the processing unit 111 of at least one unit. i. The time difference between the above temporal events related to one unit 101, ii. The time difference between the above-mentioned temporal events related to another unit 101, The fact that it is calculated by processing, c. The fact that at least one unit 101 shares information regarding the temporal event analyzed by the measuring device 109 with at least one other unit 101 via the communication device 113, It is characterized by the following.

[0042] Therefore, each light source 103 driven by the corresponding electrical circuit 105 can generate light pulses that can propagate within a sufficiently large solid angle in the space surrounding the unit, and the light pulses generated by each unit can reach the other unit even if the relative direction between the two units is unknown. To achieve this, it is clearly desirable for the light pulses to diverge rather than be parallel.

[0043] The idea of ​​using the same optical pulse in a space not limited to a single dimension overcomes the technical problems of the prior art, particularly cited European Patent Application No. 3165943, by using the system of this patent application in conjunction with the aforementioned system. This is because experts in the field, aware of European Patent Application No. 3165943, would obviously have adopted known common techniques for changing the divergence angle of optical signals, such as the use of diverging lenses, if they had attempted to extend the scope of application of European Patent Application No. 3165943. However, this solution would have resulted in low efficiency in terms of measurement speed and power consumption, mainly due to the fact that in European Patent Application No. 3165943, the same optical transmitter is used for both transmitting optical pulses useful for time difference measurement and transmitting optical information useful for optical distance calculation. In fact, this hypothesis would require a high-power optical transmitter radiating towards a wide solid angle with a significantly lower pulse rate compared to a low-power optical transmitter.

[0044] In contrast, the present invention is a. It does not necessarily presuppose the existence of a preferred emission direction for the optical signal, and it also functions when transmitting a single optical pulse, leading to power savings. b. A communication device 113 is used specifically for sharing information necessary for calculating propagation time. Therefore, since the above information is not shared using the light source 103 and the photodetector 107, the signal transmitted between them is reduced. The presence of the communication device 113, separated by the light source 103 and the optical receiver 107, enables improved speed and energy efficiency of optical pulse transmission and reception between the light source 103 and the optical receiver 107, resulting in faster and more energy-efficient measurement. The communication device 113 is not limited to the use of optical signals; rather, from an energy efficiency standpoint, since the signal is transmitted using a different channel than the light source 103, it is efficient when using signals with different bandwidths, such as Bluetooth® or Wi-Fi® signals commonly used for data transfer in local networks.

[0045] Each unit 101 further includes a photodetector 107 for detecting light pulses coming from other light sources 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.

[0046] According to a preferred embodiment of the present invention, the processing unit 111 of each unit 101 transmits a start signal to the electrical circuit 105 that drives the pulsed laser, as illustrated. Thus, the electrical circuit 105 of each unit 101 drives the pulsed laser 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.

[0047] In a preferred embodiment, it is assumed that the generation of a light pulse by the light source 103 occurs simultaneously with a sudden change in the amount of electricity in the light source 103, i.e., the current flowing through the light source 103. The photodetector 107 of each unit detects the light pulse coming from the other unit 101. In a preferred embodiment, the detection event of a light pulse causes a sudden change in the amount of electricity in the photodetector 107, the current generated by the photodetector 107, and this change is considered to occur simultaneously with the light pulse.

[0048] The measuring device 109 is connected to both the light source 103 and the photodetector 107, enabling the identification of two events associated with each other: a sudden change in the current flowing through the light source 103 and a sudden change in the current generated by the photodetector 107. Further details regarding the measuring device 109 in a preferred embodiment of the present invention will be described later.

[0049] The processing unit 111 is also connected to the measuring device 109 and the communication device 113. The processing unit 111 of unit 101a communicates wirelessly with the processing unit 111 of unit 101b.

[0050] According to a preferred embodiment of the present invention, the communication device 113 of each unit has a radio frequency antenna.

[0051] The processing unit 111 of at least one unit 101, for example unit 101b, transmits information regarding the time difference between two events identified by the measuring device 109 to the processing unit 111 of the other unit 101, in this case unit 101a, via the communication device 113. The processing unit 111 of the other unit 101, in this case unit 101a, receives information regarding the time difference between events identified by unit 101b via the communication device 113. The processing unit 111 of unit 101a calculates the propagation time of the optical pulse between the two units 101a and 101b. a. The time difference between two events identified by unit 101a, and b. The time difference between two events identified by unit 101b, Calculate by taking half the absolute value of the sum of the items.

[0052] It can be observed that the sign of the time difference between two events associated with unit 101a and the sign of the time difference between two events associated with unit 101b may be opposite.

[0053] To clarify the operating principle of this method, Figure 2 is used. Figure 2 is a diagram illustrating the principle of calculating propagation time. Specifically, it represents the optical pulses generated and received by each unit 101. In detail, Figure 2 shows a first graph and a second graph, with the upper first graph relating to unit 101a and the lower second graph relating to unit 101b. The vertical axis of each unit 101 represents the electrical quantity labeled "I" (current in a preferred embodiment), and the horizontal axis of each unit 101 represents the time axis labeled "t". To understand the operating principle, a common time axis is considered for one unit 101. However, it will be explained later that time-series synchronization between two units 101 is not necessary.

[0054] The solid line 207 in the first graph represents the current flowing through the light source 103 of unit 101a, for example, a pulsed laser. The dashed line 208 in the first graph represents the current generated by the photodetector of unit 101a. The solid line in the second graph 209 represents the current flowing through the light source 103 of unit 101b. The dashed line in the second graph 210 represents the current generated by the photodetector of unit 101b.

[0055] In the first graph, the moment when a sudden change occurs in the current flowing through the light source 103 of unit 101a is shown as t AL This is written as t, and the moment when a sudden change occurs in the current generated by the photodetector 107 of unit 101a is indicated as t AR This is how it is written. In this illustrative explanation, t AL and t AR These indicate the peaks of the respective referenced curves.

[0056] In the second graph, the moment when a sudden change in the current flowing through the light source 103 of unit 101b occurs is shown as tBL and the moment at which a sudden change in the current generated by the photodetector 107 of the unit 101b occurs is denoted by t BR In particular, in this exemplary description, t BL and t BR each indicate the peak of the referenced electrical quantity.

[0057] In the first graph, the propagation time from the unit 101a to the unit 101b and the propagation time from the unit 101b to the unit 101a are equal to each other, and these are denoted by t p .

[0058] Looking at the graph, the following description can be given.

[0059] [Formula]

[0060] The quantity (t AL -t AR ) and (t BL -t BR ) can take both positive and negative values. It should also be noted that an absolute value is required when it is not known in advance which unit 101 generates the first pulse. The quantity (t AL -t AR ) can be measured by the unit 101a, and the quantity (t BL -t BR ) can be measured by the unit 101b, so there is no need to synchronize the clocks of one unit 101 with another. The propagation time is calculated as follows.

[0061] [Formula]

[0062] Alternatively, the processing can be performed using an equivalent formula. Preferably, the processing unit 111 of at least one unit 101 can process 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, and calculate the distance between the units 101.

[0063] Therefore, by multiplying the propagation time by the propagation speed, it is possible to further calculate the distance between units 101.

[0064] Furthermore, preferably, the processing unit 111 of at least one unit 101 can calculate at least one continuous derivative with respect to time with respect to the distance between two units 101 of the system, such as velocity or acceleration, and these calculations can be initiated from information about the distance.

[0065] Several preferred embodiments are described in detail below.

[0066] [Embodiment using the time-to-digital converter 114] The embodiments of the present invention will be described in more detail below, and further details regarding the measurement process and measuring device 109 provided in each unit 101 will be provided.

[0067] According to a preferred embodiment of the present invention, Figure 3 shows a schematic diagram of one of two general-purpose units 101 of the system of the present invention, the unit 101 comprising the following: -Light source 103 such as pulsed laser, - Electrical circuit 105 for driving the light source 103, -Photodetector 107, -a. A time-to-digital converter 114 having at least two stop inputs, b. A first electrical circuit 115 for reading the amount of electricity related to the light source 103, c. A second electrical circuit 116 for reading the electrical quantity related to the photodetector 107, A measuring device 109 consisting of the above. - Processing device 111, -Communication device 113.

[0068] The time-to-digital converter 114 is a digital measuring instrument used to measure the time intervals between various types of events. These time intervals are determined by a start signal and at least one stop signal present at the input of the time-to-digital converter 114.

[0069] Here, the operation of each unit 101 will be described in the preferred embodiment described. In the embodiment described, the first electrical circuit 115 for reading out the pulsed laser or general-purpose light source 103 is characterized in that it converts the current flowing through the pulsed laser into a voltage proportional thereto and enables comparison of this voltage with a reference voltage. The first electrical circuit 115 for reading out the pulsed laser is preferably, in a non-limiting embodiment, realized by a resistor connected in series with the pulsed laser and positioned between the pulsed laser and a ground node, and a comparator that compares the voltage at a common node between the resistor and the pulsed laser with a threshold voltage.

[0070] In the described preferred embodiment, the second electrical circuit 116 for reading out the photodetector 107 is characterized in that it converts the current generated by the photodetector 107 into a proportional voltage and enables comparison of this voltage with a threshold voltage value. In the described embodiment, the second electrical circuit 116 for reading out the photodetector is implemented in a non-limiting manner by a transimpedance amplifier connected to the photodetector 107 and a comparator connected to the output of the transimpedance amplifier.

[0071] According to a preferred embodiment of the present invention, the time-to-digital converter 114 has at least one start input and at least two stop inputs. The processing unit 111 is connected to one of the start inputs of the time-to-digital converter 114. The output of a first electrical circuit for reading out the pulsed laser is connected to a stop input of the time-to-digital converter 114. The output of a second electrical circuit for reading out the photodetector 107 is connected to another 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 unit 111 to transmit the results of the digital time measurement to the processing unit 111.

[0072] In a preferred embodiment described in the present invention, a processing unit 111 within each unit 101 transmits a start signal to the start input of a time-to-digital converter 114 to initiate a time-to-digital conversion process. A digital signal delayed with respect to the start signal is transmitted by the processing unit 111 of each unit 101 to an electrical circuit 105 for driving a light source 103, which generates a current to drive the light source 103, i.e., a pulsed laser in this example.

[0073] When a current pulse flows through the pulsed laser, the first electrical circuit 115 for reading the pulsed laser generates a stop signal at the first stop input of the time-to-digital converter 114, simultaneously with the optical pulse generated by the pulsed laser.

[0074] When an optical pulse is received by the photodetector 107 of each unit 101, the second electrical 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.

[0075] To more clearly illustrate the operation of a preferred embodiment of the present invention, also refer to Figure 4. Figure 4 shows two graphs, one at the top relating to unit 101a and the other at the bottom relating to unit 101b. In each graph, the vertical axis represents voltage labeled "V" and the horizontal axis represents time labeled "t".

[0076] In particular, Figure 4 shows the following for each of the two graphs: -Time of each unit 101-Voltage at the start inputs 403, 404 of the digital converter 114, -Time of units 101a and 101b -Start moment of digital converter 114 (startA, startB), -Time of each unit 101-Voltage at the first stop inputs 405, 406 of the digital converter 114, - Stop moment (stopLA, stopLB) corresponding to the first stop input of the time-to-digital converter 114 -Time of each unit-Voltage at the second stop inputs 407, 408 of the digital converter 114, - Stop moments (stopRA, stopRB) corresponding to the second stop input of the time-to-digital converter 114.

[0077] When the stop time measurements (stopLA, stopRA) are read by the processing unit 111 of unit 101a connected to the corresponding time-digital converter 114, and the stop time measurements (stopLB, stopRB) are read by the processing unit 111 of unit 101b connected to the corresponding time-digital converter 114, the processing unit 111 of unit 101b transmits the measurements (stopLB-stopRB) to the processing unit 111 of unit 101a via the communication device 113 of unit 101b, and the processing unit 111 of unit 101a receives this transmission via the communication device 113 of unit 101a and calculates the propagation time tp as follows.

[0078]

number

[0079] In the preferred embodiments described of the present invention, the communication device 113 of each unit 101 is a radio frequency antenna. Obviously, such a communication device 113 in a different preferred embodiment may also include a computing unit separate from the processing unit 111 of the corresponding unit 101.

[0080] According to a preferred embodiment, the measurement process, initiated by the processing unit 111 of each unit transmitting a start signal to the time-to-digital converter 114 of each unit 101, is periodically repeated by the processing unit 111 of each unit 101 to obtain multiple measurements for calculating statistical parameters such as mean and variance. In this case, each unit 101 generates and detects a train of light pulses.

[0081] In more preferred and less limited embodiments of the present invention, instead of a single time-to-digital converter 114 having two stop inputs, two time-to-digital converters can be used in each unit 101. In this case, in the embodiments described, the two converters receive the same start signal from the processing unit 111.

[0082] The embodiments described above do not limit the realization of the system subject matter of the present invention. For example, in another embodiment of the present invention, start signals (start, startB) within each unit 101 may be generated internally by the time-to-digital converter 114, and a signal delayed with respect to the start signal may be generated by the time-to-digital converter 114 and transmitted to the electrical circuit 105 that drives the light source 103.

[0083] [Embodiment using the analog-to-digital converter 117] Figure 5 schematically represents two units 101, unit 101a and unit 101b of the system according to a preferred embodiment of the present invention, and provides details regarding the measuring device 109 of each unit 101.

[0084] In particular, each unit 101 includes the following: -The light source 103 is a pulsed laser, - Electrical circuit 105 for driving the pulsed laser, -Photodetector 107, -a. An analog-to-digital converter 117 having at least two input channels, b. A first electrical circuit 115 for reading the electrical quantities related to the pulsed laser, c. A second electrical circuit 116 for reading the electrical quantity related to the photodetector 107, Measuring device 109 having, - Processing device 111, -Communication device 113.

[0085] The operation of each unit 101 is shown below in accordance with the embodiments described.

[0086] In preferred embodiments of the present invention described herein, the first electrical circuit 115 for pulse laser readout is characterized in that it enables the conversion of the current flowing through the pulse laser into a voltage proportional to the pulse laser. The first electrical circuit 115 for pulse laser readout is preferably implemented, in a non-limiting embodiment, using a resistor connected in series between the pulse laser and the ground node, and a voltage amplifier that amplifies the voltage across the resistor.

[0087] In the described embodiment, the second electrical 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 thereto. In the described embodiment, this second electrical circuit 116 has a transimpedance amplifier whose input is connected to the detector in a non-limiting manner.

[0088] The processing unit 111 of each unit 101 starts the measurement upon receiving a start signal transmitted to the electrical circuit 105 that drives the pulsed laser.

[0089] 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 electrical circuit 115 for pulse laser readout and the voltage at the output of the second electrical circuit 116 for photodetector 107 readout. In this embodiment, the analog-to-digital converter 117 connected to the processing unit 111 provides the processing unit 111 with the data resulting from the digitization of the input signals.

[0090] To measure the time difference between the arrival time of a pulse measured by one channel of the analog-to-digital converter 117 and the time difference of a pulse measured by the other channel of the analog-to-digital converter 117, the processing unit 111 uses known processing techniques such as cross-correlation between the two digitized signals, or evaluates the arrival moment of each digitized pulse using a digital threshold.

[0091] The processing unit 111 of one unit 101, for example 101b, transmits the time difference between identified events to the processing unit 111 of the other unit 101, for example 101a, via the communication device 113 of each unit 101. The processing unit 111 of unit 101a then processes the propagation time. a. The time difference between events identified by unit 101a, b. The time difference between events identified by unit 101b, It is calculated as half the absolute value of the sum.

[0092] [Embodiments including optical lenses and optionally rotating mirrors] In a further embodiment, at least one unit 101 comprises an optical lens that parallelizes light pulses generated by a light source 103, and optionally a rotating mirror used to direct the parallelized beam to different angular positions with respect to a predetermined reference system fixed to the unit 101.

[0093] Therefore, according to this embodiment, in the operation configuration of the at least one unit 101 described above, the rotating mirror is used to sequentially guide the light pulses parallelized by the optical lens in different directions within a three-dimensional space that can be explored by the rotating mirror itself.

[0094] Therefore, distance measurement is performed only when the parallelized beam of one unit 101a is approximately parallel to the direction in which unit 101a is connected to another unit 101b by the operation enabled by the rotating mirror, and when the distance and orientation relative to unit 101a need to be known.

[0095] When the parallelized light pulse of unit 101a is directed in a direction substantially parallel to the direction between unit 101b and unit 101a, the latter can receive the parallelized light pulse emitted by the other unit 101a and transmit information about the measured time difference to the same unit 101a.

[0096] Therefore, by knowing the angular position adopted by the rotating mirror during measurement, the processing unit 111 can also obtain information related to the relative angular direction of the other unit 101b.

[0097] [An embodiment providing multiple light sources or detectors] If a single unit 101 comprises one single light source 103 and / or one single photodetector 107, the unit 101 may not be able to transmit and receive light pulses in all angular directions within the surrounding space. Therefore, in such cases, it is advantageous to have the same unit 101 comprise two or more light sources 103 and / or two or more photodetectors 107 so that the transmitted and / or received light pulses can cover a wider solid angle.

[0098] This allows for increased reliability of the system, which is the subject of this invention, through redundancy, and maximizes the observation area of ​​the solid angle.

[0099] Multiple light sources 103 can be driven by the electrical circuit 105 within the unit 101 as if they were a single light source 103, or as if they were multiple different electrical circuits 105 operating simultaneously.

[0100] Each photodetector 107 may instead be connected to the same measuring device 109 that identifies a first pulse from among the pulses received from one of the photodetectors belonging to the same unit 101. If the fields of view of the photodetectors 107 do not overlap, only one of the photodetectors 107 will identify a pulse coming from another unit 101.

[0101] [Methods for performing triangulation or trilateration] According to the embodiment covered by claim 8, the distances obtained between at least three different units 101 can be used for geometric and topological processing (such as triangulation or trilateration) to determine the position of any one of the units 101 and further topological information of the system composed of the different units 101.

[0102] As an example, in a particularly advantageous embodiment, the system consists of four units 101, of which three units 101 are fixed and one unit 101 is movable in two-dimensional space, so that the distance measured between each of the movable unit 101 and the fixed unit 101 makes it possible to uniquely identify the position of the movable unit 101 in two-dimensional space.

[0103] In detail, it should be noted that three units are sufficient only when the moving unit moves within a one-dimensional space where one moving unit and two stationary units are required in that one-dimensional space.

[0104] Similarly, if the movable units are movable in two-dimensional space, four units are needed—three fixed and one movable. However, in three-dimensional space, five units are needed—four fixed and one movable.

[0105] [An embodiment for detecting different degrees of freedom of a rigid subsystem] According to an embodiment of the present invention covered by claim 9, several units 101 of the system covered by the present invention are arranged relative to each other at fixed distances and angles in order to realize at least one rigid subsystem, i.e., a subsystem in which at least two units 101 have fixed distances and orientations relative to each other. In this way, by combining knowledge of the distance between each unit 101 belonging to the rigid subsystem and at least one unit 101 not belonging to the subsystem, and knowledge of the relative positions of the units 101 belonging to the rigid subsystem, it becomes possible to detect the translational and rotational degrees of freedom of the rigid subsystem with respect to at least one unit 101 not belonging to the subsystem.

[0106] In fact, since the relative positions of the units 101 constituting the rigid subsystem are known, if, for example, one unit 101 not belonging to the rigid subsystem has its distance from each of the two units 101 belonging to the subsystem determined, then if the rigid subsystem has only rotational degrees of freedom and no translational degrees of freedom, it is possible to estimate the orientation of the rigid subsystem from that distance. If there are two units 101 not belonging to the rigid subsystem, and the rigid subsystem has only one translational degree of freedom, then it is possible to estimate the position of the rigid subsystem relative to the two units 101 not belonging to the subsystem.

[0107] If there are multiple units 101 belonging to the rigid subsystem, and / or multiple units 101 not belonging to the subsystem, it is possible to further estimate more rotational and / or translational degrees of freedom of the rigid subsystem for at least one unit 101 not belonging to the rigid subsystem.

[0108] For example, the rigid subsystem may be rigidly connected to a moving body whose position and orientation in space over time need to be known.

[0109] For illustrative purposes, Figure 6 shows a system comprising five units 101a, 101b, 101c, and 101d, which includes a rigid subsystem consisting of four units 101a, 101b, 101c, 101d, and 101e. In this rigid subsystem, the relative positions between the four units 101a, 101b, 101c, and 101d are known. Unit 101e does not belong to the rigid subsystem.

[0110] In a preferred embodiment, units 101a, 101b, 101c, and 101d belonging to the rigid subsystem operate sequentially, where operation means transmitting optical pulses, while unit 101e is always operating.

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), wherein each unit (101) is a. Light source (103), b. An electrical circuit (105) that drives the light source (103) by an electrical signal, c. A photodetector (107) that detects 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 temporal events, e. Processing device (111), f. Communication device (113) and, Equipped with, The aforementioned temporal events are, i. Sudden changes in the amount of electricity related to the light source (103), ii. Sudden changes in the electrical quantity related to the photodetector (107), Associated with, 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 controlled by the processing unit (111) of at least one unit (101). a. The time difference between the aforementioned time events related to one unit (101), b. The time difference between the aforementioned temporal events related to another unit (101), It is calculated by processing the data. At least one unit (101) shares information about temporal events analyzed by the measuring device (109) with at least one other unit (101) via the communication device (113). system.

2. The system according to claim 1, wherein the processing device (111) of at least one unit (101) processes the propagation time of an optical pulse in the space between two units (101) and the propagation speed of an optical pulse in the space between the units (101), and calculates the distance between the units (101).

3. The system according to claim 2, wherein a processing unit (111) of at least one unit (101) calculates at least one time-sequential derivative of the distance between two units (101) in the system.

4. At least one measuring device (109) of unit (101) a. At least one time-to-digital converter (114), b. A first electrical circuit (115) for reading the amount of electricity related to the light source (103), c. A second electrical circuit (116) for reading the electrical quantity related to the photodetector (107), A system according to any one of claims 1 to 3, including the system described in any one of claims 1 to 3.

5. At least one measuring device (109) of unit (101) a. At least one analog-to-digital converter (117), b. A first electrical circuit (115) for reading the amount of electricity related to the light source (103), c. A second electrical circuit (116) for reading the electrical quantity related to the photodetector (107), A system according to any one of claims 1 to 3, including the system described in any one of claims 1 to 3.

6. At least one unit (101) further comprises an optical lens for parallelizing the light pulses generated by the light source (103), The system according to any one of claims 1 to 5.

7. The system according to claim 6, wherein at least one unit (101) further comprises a rotating mirror for guiding the parallelized light pulses to different angular positions.

8. The system comprises at least three units (101), and the distance between units (101) belonging to different pairs is processed by geometric processing. a. The position of at least one specific unit (101) in space, b. At least one of the continuous derivatives with respect to time with respect to the position, The system according to claim 2, which determines at least one of the quantities of .

9. It comprises at least three units (101), where at least two units (101) are arranged relative to each other at a fixed and known distance and angle to realize at least one rigid subsystem, and by a geometric procedure, a. The spatial position of at least one unit (101) belonging to one rigid subsystem, b. At least one continuous derivative with respect to time with respect to the spatial position of at least one unit (101) belonging to at least one rigid subsystem, c. The spatial orientation of at least one rigid subsystem, d. At least one continuous derivative with respect to time with respect to the direction in space of at least one rigid subsystem, The system according to claim 2, which is capable of calculating at least one of the amounts of

10. The system according to any one of claims 1 to 9, wherein each unit (101) comprises a plurality of light sources (103).

11. The system according to any one of claims 1 to 10, wherein each unit (101) comprises a plurality of photodetectors (107).

Images