NL2019681B1 - A system, a method and a computer program product for detecting an object - Google Patents

Abstract

The invention relates to a system for detecting an object. The system comprises a multiple number of optical transmitters for transmitting optical beams. Further, the system comprise a multiple number of optical receivers for receiving the transmitted optical beams. Also, the system comprises a detection unit that is arranged for registering an interruption of receipt of a transmitted optical beam. Each receiver is operationally optically coupled to a corresponding transmitter such that each receiver and its corresponding transmitter form a virtual beam detector.

Description

Title: A system, a method and a computer program product for detecting an object

The invention relates to a system for detecting an object.

Typically, valuable objects such as paintings in a museum are protected by IR or visible light camera systems. However, it appears that such security systems suffer from a number of drawbacks such as blind spots and false warnings. Further, personal is needed to instantly monitor images of the camera systems.

It is an object of the invention to provide a system for detecting an object wherein at least one of the above identified disadvantages is counteracted. Specifically, it is an object to provide a system for detecting an object that is more accurate. Thereto, according to the invention, a system is provided for detecting an object, comprising a multiple number of optical transmitters for transmitting optical beams and a multiple number of optical receivers for receiving the transmitted optical beams, further comprising a detection unit that is arranged for registering an interruption of receipt of a transmitted optical beam, wherein each receiver is operationally optically coupled to a corresponding transmitter such that each receiver and its corresponding transmitter form a virtual beam detector.

By providing a detection unit for registering an interruption of receipt of a transmitted optical beam, wherein each receiver is operationally optically coupled to a corresponding transmitter such that each receiver and its corresponding transmitter form a virtual beam detector, a system is obtained detecting objects protruding through the virtual beam. As the transmitters and receivers can be located quite close before the valuable object, no blind spots occur, thereby improving the detection security.

Advantageously, each transmitter can be arranged for transmitting an optical beam that is uniquely coded relative to optical beams transmitted by other transmitters. By further arranging the receivers for operationally optically couphng to a transmitter transmitting a beam having a code that matches with a pre-determined code associated with said receiver, a limited number of transmitter / receiver pairs can be obtained, in a controllable way, so that only a limited number of beams associated with said transmitter I receiver pairs have to be monitored for interruption detecting, thus efficiently using processing power of the detection unit. Further, a desired set of optical beams forming a web in a detection area can be realized for effectively performing object detection in a detection area.

The system is widely applicable for securing objects or spaces against intrusion by vehicles, animals and persons crossing said beam, thereby being capable of determining intrusion situations.

The invention also relates to a method for detecting an object.

Further, the invention relates to a computer program product. A computer program product may comprise a set of computer executable instructions stored on a data carrier, such as but not limited to a flash memory, a CD or a DVD. The set of computer executable instructions, which allow a programmable computer to carry out the method as defined above, may also be available for downloading from a remote server, for example via the Internet, e.g. as an app.

Other advantageous embodiments according to the invention are described in the following claims.

It should be noted that the technical features described above or below may each on its own be embodied in a system for detecting an object, i.e. isolated from the context in which it is described, separate from other features, or in combination with only a number of the other features described in the context in which it is disclosed. Each of these features may further be combined with any other feature disclosed, in any combination.

The invention will now be further elucidated on the basis of a number of exemplary embodiments and an accompanying drawing. In the drawing:

Fig. 1A shows a schematic view of a first embodiment of a system for detecting an object according to the invention;

Fig. IB shows a schematic view of a second embodiment of a system for detecting an object according to the invention;

Fig. 1C shows another schematic view of the system for detecting an object as shown in Fig. 1A;

Fig. 2 shows a schematic view of a third embodiment of a system for detecting an object according to the invention;

Fig. 3 shows a schematic view of a fourth embodiment of a system for detecting an object according to the invention;

Fig. 4 shows a schematic view of a fifth embodiment of a system for detecting an object according to the invention;

Fig. 5A shows a schematic perspective view of a system for detecting an object according to the invention including an elongate carrying structure;

Fig. 5B shows a schematic cross sectional view of the system for detecting an object as shown in Fig. 5A;

Fig. 5C shows a schematic side view of the system for detecting an object as shown in Fig. 5A;

Fig. 6 shows a schematic perspective view of a system for detecting an object according to the invention surrounding a three-dimensional detection space;

Fig. 7 shows a schematic perspective view of a system for detecting an object according to the invention including two virtual wall detectors arranged behind each other;

Fig. 8 shows a schematic perspective view of a system for detecting an object according to the invention including a pyramidal shaped virtual cover detector, and

Fig. 9 shows a flow chart of a method according to the invention.

The figures merely illustrate preferred embodiments according to the invention. In the figures, the same reference numbers refer to equal or corresponding parts.

Figure 1A shows a schematic view of a first embodiment of a system 1 for detecting an object according to the invention. The system 1 has a multiple number of optical transmitters 2a-d for transmitting optical beams 3a-d. Further, the system 1 has a multiple number of optical receivers 4a-d for receiving the optical beams 3a-d. The optical transmitters 2a-d are located as a one-dimensional array along a first line 5, with equidistant intermediate spaces. Similarly, the optical receivers 4a-d are located as a one-dimensional array along a second line 6, with equidistant intermediate spaces. The first and second line 5, 6 are mainly parallel defining a two-dimensional detection area 10 therebetween. In a direction Y, parallel to the first and second line 5, 6, the detection area 10 is bounded by a first and second side line 7, 8 interconnecting the first and second line 5, 6 beyond the location of the transmitters 2 and receivers 4, respectively. Generally, optical transmitters 2 are depicted as crosses while optical receivers 4 are depicted as open circles.

The system 1 further has a detection unit 9 that is arranged for registering an interruption of receipt of a transmitted optical beam 3a-d. The combination of optical beams 3a-d form a virtual wall or curtain that notifies any object traversing therethrough. Thereto, the detection unit 9 is connected to the receivers 4a-d. In the shown embodiment, the detection unit 9 is also connected to the transmitters 2a-d for controlling a process of transmitting the optical beams 3a-d. Based on interruption data, the detection unit 9 may estimate static and/or dynamic characteristics of an object causing the beam interruption as described in more detail below.

Each receiver 4a-d is operationally optically coupled to a corresponding transmitter 2a-d such that each receiver 4a-d and its corresponding transmitter 2a-d form a virtual beam detector.

Generally, each transmitter 2a-d is arranged for transmitting an optical beam 3a-d that is uniquely coded relative to optical beams transmitted by other transmitters. Then, the optical beams are mutually different and each beam can be uniquely associated with the respective transmitter that has transmitted said beam. By coding the transmitted beams a limited number of virtual beam detectors can be obtained, in a controllable way, i.e. the number of optically coupled transmitter / receiver pairs is limited so that only a limited number of beams have to be monitored for detecting any interruption, thus efficiently using processing power of the detection unit 9 arranged for performing interruption detection.

Optical beams can e.g. be coded in a spectral or temporal way. As an example, the transmitted beams 3a-d may have a different colour or wavelength. Further, the transmitted beams 3a-d may be modulated in time, e.g. using a pulse code modulation or other unique binary code modulating the intensity of the beam over time. By transmitting a beam in accordance with a specific code, said beam can uniquely be distinguished from other beams.

Each of the receivers 4a-d is arranged for operationally optically coupling to a transmitter 2a-d transmitting a beam 3a-d having a code that matches with a pre-determined code associated with said receiver. A process of filtering and processing the received coded beams can be performed in a digital regime, after a step of analogue to digital conversion, by a processingunit, integrated with hardware optically receiving the beam, or by a processing unit remote from hardware optically receiving the beam, e.g. by a processing element in the detection unit 9. Then, during operation of the system 1, each of the receivers 4a-d optically couples to a transmitter transmitting a beam having a pre-determined code that is associated with the respective receiver. On the other hand, the respective receiver does not optically couple to a transmitter transmitting a beam having a code that does not match with the pre-determined code associated with the respective receiver. In other words, the respective receiver completely ignores beams originating from transmitters not corresponding to the code associated with the receiver, Then, the number and location of optically coupled transmitter I receiver pairs can be selected, thus realizing a desired set of optical beams forming a web in the two-dimensional detection area 10 for effective objection detection. As an example, a substantially uniform distribution over the detection area 10 can be obtained. As a further example, some sub-areas in the detection area 10 can be provided with a more dense beam distribution or a less dense beam distribution

As an example, the transmitters 2a-d shown in Fig. 1A transmit a beam at a first, second, third and fourth frequency, respectively. Similarly, the receivers 4a-d are set to couple to a transmitter transmitting at a first, second, third and fourth frequency, respectively, in accordance with a respective frequency code associated with the individual receivers 4a-d. Then, a first receiver 4a optically couples to a first transmitter 2a, a second receiver 4b optically couples to a second transmitter 2b, a third receiver 4c optically couples to a third transmitter 2c, and a fourth receiver 4d optically couples to a fourth transmitter 2d. Also pulse coded beams can be recognized by the receivers, using digital filtering. As a result, a limited number of mutually coupled transmitters and receivers are obtained.

In this respect it is noted that the system may include more or less than four transmitters, e.g. three, five, six, or even more transmitters, e.g. tens, hundreds or thousands of transmitters. Similarly, the system may include more or less than four receivers, e.g. three, five, six, or even more receivers, e.g. tens, hundreds or thousands of receivers. Further, the number of transmitters may be different from the number of receivers.

The detection unit 9 is arranged for registering an interruption of optical beam receipt in the virtual beam detector, i.e. an interruption of an optical beam that is transmitted and received, respectively, by a transmitter and a receiver, respectively, of a transmitter I receiver pair that is operationally optically coupled.

In the embodiment shown in Fig. 1A, the transmitters 2a-d and receivers 4a-d are distributed along a detection contour including two detection contour segments, viz. the parallel first and second line 5, 6, extending in a common plane, surrounding a two-dimensional detection area 10. The system 1 including the transmitters 2, receivers 4 and detection unit 9 form a virtual wall detector that detects an object present in the detection area and interrupting at least one optical beam 3.

It is noted that, as an alternative to the setup shown in Fig. 1A, each receiver 4a-d can be replaced by a series of receivers that are operationally optically coupled to the respective transmitter 2a-d. Then, the second line 6 can completely or mainly completely be covered with receivers.

Figure IB shows a schematic view of a second embodiment of a system 1 for detecting an object according to the invention. The system 1 is similar to the system 1 shown in Fig. 1A. However, in Fig. IB, the transmitters 2 and receivers 4 are distributed over both the first and the second line 5, 6. In the shown embodiment, the transmitters 2 and receivers 4 are positioned in a linear array, in an alternating manner. However, the transmitters 2 and receivers 4 can also be distributed in another manner, e.g. such that the first line 5 contains more transmitters 2 than receivers 4, while the second line 6 contains more receivers 4 than transmitters 2.

The transmitter and receiver setups shown in Fig. 1A and Fig. IB are also referred to as a so-called duo-frame for determining a position of an object in a direction Y parallel to the first and second line 5, 6. Further, in the embodiments shown in Fig. 1A and Fig. IB, each receiver is optically coupled to a unique transmitter, thus forming four transmitter-receiver pairs that are optically coupled during operation.

Fig. 1C shows another schematic view of the system 1 for detecting an object as shown in Fig. 1A. For illustration purposes only two transmitters 2a’,2b’ and two receivers 4a’,4b’ are shown. Each transmitter 2a-b includes an optical source 2a’, 2b’ transmitting an optical beam upon receipt of an analogue feeding signal. Further, each transmitter 2a-b includes a digital to analogue converter 17a, 17b connected to a corresponding optical source 2a’, 2b’ and converting a digital transmitting control signal into an analogue feeding signal feeding the respective optical source 2a’, 2b’. Similarly, each receiver 4a, 4b includes an optical sensor 4a’, 4b’ and an analogue to digital converter 18a, 18b connected to a respective optical sensor 4a’, 4b’. Upon receipt of an optical beam, the analogue to digital converter 18a, 18b converts the electric sensing signal from the optical sensors 4a’, 4b’ into a digital sensor signal for processing. The system 1 further comprises a processing module 9’ connected to the digital to analogue converters 17a, 17b and to the analogue to digital converters 18a, 18b. The processing module 9’ transmits the digital transmitting control signals towards the digital to analogue converters 17a, 17b of the transmitters 2a,b, and receives the digital sensor signals received from the analogue to digital converters 18a,b of the receivers 4a,b. Further, the processing module 9’ processes the received digital sensor signals, including a filtering step, e.g. a sub-step of decoding the sensor signals and a sub-step of comparing the code with a pre-determined code associated with the receiver sending the digital sensor signal. If the code matches with the predetermined code associated with the receiver, the processing module 9’ registers that the receiver is optically coupled to the transmitter transmitting the coded beam. Otherwise, no optical coupling is registered rendering the receiver virtually insensible for the transmitted beam having a code that does not match.

The system 1 further includes a control module 9” connected to the processing module 9’ for controlling operation of the processing module 9’. Further, the system 1 includes a system interface 9”’enabling a user to interact with the system 1, e.g. by activating or diagnosing the system, or by receiving an alert signal if an object has been detected by the system. The processing module 9’, the control module 9” and/or the interface module 9”’ can be implemented separately as shown in Fig. 1C or can at least partly be integrated, e.g. into a single detection unit 9 shown in Fig. 1A.

It is noted that, alternatively, any processing and/or filtering step can in principle be performed by hardware included with the individual receivers, or with a group of individual receivers.

In Fig. 1C, only two transmitters 2a’,2b’ and two receivers 4a’,4b’ are shown, for illustration purposes. In principle, the processing module 9’ can be connected to more than two transmitters and/or receivers each provided with a corresponding digital to analogue converter or analogue to digital converter can be connected. Further , a multiple number of processing modules 9’ can be connected to the control module 9” or multiple control modules can be mutually connected so that a selected number of optical transmitter / receiver couplings can be realized. Further, the interface module 9”’ can be coupled to a multiple number of processing modules for obtaining a single interface to be operated.

Fig. 2 shows a schematic view of a third embodiment of a system 1 for detecting an object according to the invention. Here, transmitters 2a-d are positioned as a one-dimensional array along a third line 5’, parallel to an X direction, transverse to the Y direction. Similarly, receivers 4a-d are positioned as a one-dimensional array along a fourth line 6’, parallel to the third line 5’. Again, a detection area 10 is bounded by a third and fourth side line 7’, 8’ interconnecting the third and fourth line 5, 6, beyond the transmitters and receivers, respectively. The system 1 including the transmitters 2, receivers 4 and detection unit 9 again form a virtual wall detector that detects an object present in the detection area 10 and interrupting at least one optical beam 3.

The transmitter and receiver setup shown in Fig. 2 is also referred to as a so-called duo-frame for determining a position of an object mainly in a direction X transverse to the third and fourth side line 7’, 8’. It is noted that, again, the transmitters and receivers can be distributed in another manner over the third and fourth line 5’, 6’, e.g. in an alternating manner.

Further, in the embodiment shown in Fig. 2, a single receiver is operationally optically coupled to a multiple number of transmitters. As shown, a second receiver 4b receives three optical beams transmitted by three respective transmitters 2a-c. Here, the second receiver is arranged for optically coupling to three transmitters 2a-c transmitting beams with different codes. As an example, the receiver may be simultaneously optically coupled to a transmitter transmitting a first beam 3b having a first code, e.g. having a first wavelength or first pulse code modulation, a second beam 3c having a second code, e.g. having a second wavelength or second pulse code modulation, and a third beam 3d having a third code, e.g. having a third wavelength or third pulse code modulation. In practice, the transmitters 2a-c can be arranged to transmit the respective beams after each other so that codes of the individual beams can be properly recognized by the receiver without being disturbed by other beams having other codes. Apparently, a multiple number of transmitters 2a-c are operationally optically coupled to a specific receiver 4b. Here, a single receiver 4b is arranged for operationally optically coupling to a multiple number of transmitters 2b-d each transmitting a beam 3b-d having a unique code relative to other beams. In other words, the single receiver 4b optically couples to a multiple number of transmitters 2b-d each transmitting a beam 3b-d having a pre-determined code that is associated with the receiver 4b. Here, a multiple number of pre-determined codes is associated with the receiver 4b. Again, the respective receiver 4b does not optically couple to a transmitter transmitting a beam having a code that does not match with the pre-determined codes associated with the respective receiver. In other words, the respective receiver 4b completely ignores beams originating from transmitters not corresponding to the code associated with the receiver 4b.

If two transmitters are remote from each other so that the beams transmitted by said two transmitters do not reach each other, or if the optic beams transmitted by two transmitters are directed to different directions without traversing each other, said two transmitters may operate independent of each other, even if they are coded in the same way. Then, as example, multiple transmitter receiver pairs may be formed with optical beams that have the same code.

In the embodiment shown in Fig. 2, also a multiple number of receivers 4a-b are operationally optically coupled to a specific transmitter 2a. Then, both receivers 4a-b are arranged for operationally optically coupling to the same transmitter 2a transmitting a beam 3a-b having a unique code.

Figure 3 shows a schematic view of a fourth embodiment of a system 1 for detecting an object according to the invention. Here, the transmitters 2 and receivers 4 are positioned along a one-dimensional array along the first line 5, the third line 5’ and the second line 6. The two-dimensional detection area 10 is surrounded by the first line 5, the third line 5’, the second line 6 and the first side line 7, 8 interconnecting the first and second line 5, 6. The system 1 including the transmitters 2, receivers 4 and detection unit 9 form a virtual wall detector that detects an object present in the detection area 10 and interrupting at least one optical beam 3. Here, an X coordinate as well as an Y coordinate of the object can be determined. The transmitter and receiver setup shown in Fig. 3 is also referred to as a so-called triple-frame for determining X and Y coordinates of an object in the detection area 10.

Transmitters 2 and receivers 4 can be operationally optically coupled as indicated above, preferably such that the beams are evenly distributed over the detection area 10.

Figure 4 shows a schematic view of a fifth embodiment of a system 1 for detecting an object according to the invention. Here, the transmitters 2 and the receivers 4 are distributed over a closed contour enclosing a two-dimensional detection area 10 of the virtual wall detector. The closed contour is formed by the first and second line 5, 6 and the third and fourth line 5’, 6’. Again, the transmitters 2 and receivers 4 can be distributed more evenly over the contour, e.g. in an alternating manner. Similar to the embodiment shown in Fig. 3, both an X coordinate as well as an Y coordinate of the object can typically be determined. The transmitter and receiver setup shown in Fig. 4 is also referred to as a so-called quadframe for determining X and Y coordinates of an object in the detection area 10.

Generally, a virtual wall detector includes a multiple number of optical transmitters and a multiple number of optical receivers positioned on a contour surrounding a two-dimensional detection area, also called window. Further, the virtual wall detector includes a detection unit that is arranged for registering an interruption of receipt of an optical beam transmitted by an optical transmitter and received by an optical receiver that is operationally optically coupled to a corresponding transmitter such that each receiver and its corresponding transmitter form a virtual beam detector. The contour may be rectangular as shown in Fig. 1-4, or may have another shape such as a polygon with another number of vertices such as a triangle, a pentagon or a hexagon, or a curved shape such as an ellipse or circle. In practice, the transmitters and receivers can be positioned in a row on a mast, pillar, floor, wall and/or ceiling.

By providing a virtual wall detector any person, animal, vehicle such as drone, or other object traversing said detection window can be detected, in principle, using a non-physical or even invisible barrier.

It is noted that the transmitters and receivers can be arranged in an alternative way, not on a contour surrounding in a two-dimensional detection area. As an example, transmitters and corresponding receivers can be positioned in a three dimensional space such as a hall or room, at random, creating a three-dimensional beam configuration throughout a three-dimensional space to be protected.

Generally, the system is a combination of a single or a multiple number of transmitter receiver optically coupled pairs.

Figure 5A shows a schematic perspective view of a system 1 for detecting an object according to the invention including a mainly elongate carrying structure 11. In said elongate carrying structure 11, groups of transmitters 2 and groups of receivers 4 are located at mutual different levels. Here, a first group 12 including six transmitters 2 is located in the elongate carrying structure 11, at a first level in a longitudinal direction L of the elongate carrying structure 11. A second group 13 including six receivers 4 is located at a subsequent, second level in the longitudinal direction L. Further, a third group 14 includes six transmitters 2 and is located at a third level in the longitudinal direction L. Similarly, a fourth group 15 includes six receivers 4 and is located at a fourth level in the longitudinal direction L. Generally, the groups 12-15 are located as a one-dimensional array in the elongate carrying structure 11, at subsequent levels in the longitudinal direction. In the shown embodiment, groups including transmitters and receivers, respectively, are located in an alternating manner. However, in another embodiment, the groups may ordered in another way, e.g. groups including transmitters located adjacent each while groups including receivers are also located adjacent each other, as clusters of transmitters and receivers, respectively. Further, a group located at a level in the longitudinal direction of the elongate carrying structure may include a combination of transmitters and receivers. It is noted that the above-mentioned groups may include less than six transmitters or receivers, e.g. four or five transmitters or receivers, or more than six transmitters or receivers, e.g. seven, eight or ten transmitters or receivers.

Generally, the elongate carrying structure 11 may include a combination of transmitters and receivers. However, in principle, a first elongate carrying structure 11 may include only transmitters without receivers, while a second elongate carrying structure 11 may include only receivers without transmitters.

Figure 5B shows a schematic cross sectional view of the system 1 for detecting an object as shown in Fig. 5A. Here, the first group 12 including transmitters 2 and the second group 13 including receivers 4 is shown. In the shown embodiment, the transmitters 2a-f, in the first group 12, and the receivers 4a-f, in the second group 13, are distributed in an uniform manner in a circumferential direction C with respect to the longitudinal direction L. Further, the transmitters 2a-f are located such that they form vertices of a regular hexagon. Similarly, the receivers 4a-f are located such that they form vertices of a regular hexagon. It is noted that they may also form vertices of a non-regular hexagon. Generally, the transmitters 2 and/or receivers 4 in a group at a specific level in the elongate carrying structure 11 form a polygon, preferably a regular polygon.

Further, in the embodiment shown in Fig. 5B, the polygon vertices 2a-f of the first group 12 are located mainly half-way between adjacent vertices 4a-f of the second group 13, viewed in the circumferential direction C. Generally, vertices of a subsequent group 13 may be located mainly half-way between circumferentially adjacent vertices of a previous group 12 in the order of groups located at subsequent levels in the elongate carrying structure 11. Alternatively, the vertices in subsequent groups can be located in another way, e.g. mutually aligned in the longitudinal direction L.

The embodiment shown in Fig. 5B can be obtained by providing an elongate carrying structure wherein the groups with transmitters and receivers are aligned in the longitudinal direction L, and then twisting the structure to a degree such that the vertices of a particular group are swiveled over a circumferential distance half-way between the vertices of a subsequent group.

Preferably, the elongate carrying structure 11 is flexible such that it can be brought in a specific contour, e.g. a straight contour, a curved contour or a bended contour. The structure 11 may include transparent plastic material, e.g. covering a elongate kernel, such as including a single or a multiple wire kernel. Optionally, the transmitters and receivers are embedded in the elongate carrying structure. Then, a plastic transparent material may partially cover the transmitters and receivers, functioning as optics through which optical beams from transmitters and to receivers propagate. The plastic transparent material may include a band pass filter passing an optical beam in a spectral band in which the transmitters and/or receivers operate. The optics may include a lens narrowing an aperture of the optical transmitters and receivers. As an example, an aperture of a transmitter or receiver is circa 360° divided by the number of transmitters and receivers in two subsequent groups in the elongate carrying structure 11. As an alternative, micro cylinders may be applied in front of the transmitters and/or receivers for limiting the optical aperture. In the embodiment shown in Fig. 5B the number of transmitters and receivers per group, at a specific level in the elongate carrying structure 11, is six, rendering the number of transmitters and receivers in two subsequent groups twelve. Then, an aperture of 30° may be applied. If, in another embodiment, the total number of transmitters and receivers in the two groups is eight, an aperture of 45° may be applied. Further, in yet another embodiment, the total number of transmitters and/or receivers in a single group, at a specific level, may cover 360°. Then, if the single group includes e.g. 8 transmitters and receivers in total, an aperture of 45° may be applied.

Advantageously, the transmitters are implemented as LED’s providing a robust and reliable optical performance at relatively low costs. The receivers can be implemented as photo sensors or photo sensor arrays such as linear CCD units or DLP’s. In practice, each transmitter and each receiver can be provided with a digital analogue converter and a analogue digital converter, respectively.

Figure 5C shows a schematic side view of the system 1 for detecting an object as shown in Fig. 5A. Here, the system 1 includes an elongate carrying structure 11 as described above, arranged as a pillar in a vertical direction. Further, the system includes a reflecting line 16 bounding a two-dimensional detection area 10. Then, beams 3A,B transmitted by transmitters 2 in the elongate carrying structure 11 may travel through the detection area 10, reflect against the reflecting line 16, and travel back to the elongate carrying structure 11, towards a receiver 2.

The elongate carrying structure 11 may also be applied in an embodiment described referring to Fig. 1A, IB and 2-4. It is further noted that an embodiment described referring to Fig. 1A, IB and 2-4 may include a reflecting line 16 as described above, e.g. along a side of the contour surrounding the two-dimensional detection area.

Figure 6 shows a schematic perspective view of a system 1 for detecting an object according to the invention surrounding a three-dimensional detection space 20. The system 1 includes a multiple number of virtual wall detectors 2 la-d arranged next to each other, side by side. In the shown embodiment, vertical sides 22 of the virtual wall detectors 2 la-d are connected to each other such that a series or concatenation of virtual wall detectors 2 la-d is formed. In the shown embodiment, four virtual wall detectors are connected to each other forming a ring surrounding the three dimensional detection space 20 in lateral directions X and Y. It is noted that the ring may include less than four virtual wall detectors, e.g. three virtual wall detectors, or more than four virtual wall detectors, e.g. five or six virtual wall detectors. It is further noted that the series of virtual wall detectors may be closed or open. In the shown embodiment, the virtual wall detectors have rectangular geometry. In other embodiments, virtual wall detectors having other shapes may be used, e.g. triangular shaped virtual wall detectors or polygon shaped virtual wall detectors having more than four vertices, such as a pentagonal or hexagonal shaped virtual wall detector. Generally, the combined detectors surround a three-dimensional detection space 20, forming a virtual cover detector, forming a three-dimensional cover or shield with respect to the three-dimensional detection space 20. In yet a further embodiment, the system 1 may include a ring shaped combination of virtual wall detectors 21a-d as well as a further virtual wall top detector bounding the detection space 20 at its top and having sides that are connected to the upper sides 23a-d of the ring type detectors 21. Then, the three-dimensional space 20 can be completely shielded from above and side directions. The combination of virtual wall detectors may then form a closed shield that is only open at the bottom side of the space 20. As an example, the virtual wall detectors may form a box that is open at its bottom. It is further noted that, the system may include a further virtual wall detector closing off the bottom of the three-dimensional detection space 20, thereby obtaining a truly closed shielding structure shielding the three-dimensional detection space 20 in its three dimensions.

In principle, the system 1 can be constructed easily and quickly, without high accuracy, at any location, using either a light, low cost construction or a more robust construction that may endure critical weather circumstances. Due to optical divergence of the beams, the transmitters and receiver are allowed to move somewhat without limiting its functionality. In principle, the system may operate in a robust and safe manner. Further, in principle, the detection principle can be operated without performing calibration procedures. The system 1 may have a temporal, semi-permanent or permanent character, e.g. for shielding a temporary military encampment or a military barrack, respectively.

Further, in principle, the system 1 may have any size and can function in a modular way, enabling modular extension at a later stage, scaling up or down. Also the detection accuracy can be scaled up or down, by rearranging transmitters and receivers. The system can be integrated relatively simple with existing architecture and infrastructure, while, in principle, no moving parts are included.

The described system can be applied for compound fencing of military or civil areas, installations or plants on enemy soil. Application of the system enables real time detection of incoming hostile projectiles, as well as size, speed and direction of the projectiles, thereby enabling persons to react adequately avoiding or counteracting chaotic situations. In principle, any number of incoming projectiles can be detected.

Similarly, the system can be applied for compound fencing of refugee camps, industrial plants such as chemical plants and refineries, company infrastructure, areas, ports and airports, e.g. for the purpose of estimating a number of people and/or vehicles that has entered an area.

Further, the system can also be applied for securing streets, public or private buildings such as government buildings, prisons and private houses or rural estates, halls and objects, indoors, outdoors, at sea or under water. As an example, uncultivated private or public areas can be protected, such as an intermediate space between a building and a public area. Further, the interior of building such as museums or nuclear plants can be protected. Here, a single virtual wall detector can be applied e.g. extending in a horizontal direction for monitoring a floor, ceiling or roof area, or extending in a vertical direction for monitoring vertical structures such as paintings or other valuable art on a wall, also when public is present.

In security applications, a camera system can be controlled to be swiveled automatically to an intrusion location when an intruding object or person is detected by the system. After closing hours of a publically accessible space such as a museum hall, a monitoring function can be extended to a greater space or area.

The system can also be applied for traffic control, e.g. for determining vehicle speed, lane position and/or exterior contour detection of driving vehicles, e.g. on highways, optionally in combination with existing camera systems. Advantageously, vehicle speed, trajectory control, lane control and lane load can be determined relatively accurately. In this process, vehicle contour detection can be used for road management in terms of types and number of vehicles that use the road. Optionally, also undesired vehicle driver’s behaviour can be monitored including trucks passing vehicles when prohibited and tailgating.

In another application, the system is used for measuring a size and/or movement of microbiologie tissue or organism.

In yet a further application, the system is used as a single or double virtual wall detector as described in more detail referring to Fig. 7, but orientated in a horizontal plane, above a floor of a sport accommodation or physiotherapist’s office for monitoring and/or measuring specific movements of sportsman, sportswoman or patients, e.g. for measuring jumping, landing, step and locomotion of the human body, or for measuring a force exerted by a human foot.

Figure 7 shows a schematic perspective view of a system 1 for detecting an object according to the invention including two virtual wall detectors 31, 32 arranged behind each other, preferably in a parallel constellation. Here, the virtual wall detectors 31, 32 are arranged with an offset with respect to each other. When an object 35 follows an object path 36 traversing through the first or front virtual wall detector 31 and the second or back virtual wall detector 32, said object 35 crosses the first and second virtual wall detector 31, 32 at crossing points 37a, 37b, respectively. Upon detection of said crossing points 37a, 37b, information about direction and speed of the object 35 can be obtained.

It is noted that the double virtual wall detector shown in Fig. 7 can be used as an elementary unit for building a structure surrounding a three-dimensional detection space, e.g. as illustrated in Fig. 6.

Figure 8 shows a schematic perspective view of a system 1 or detecting an object according to the invention including a pyramidal shaped virtual cover detector 41. Again, the system includes a combination of virtual wall detectors 42. Here, the individual virtual wall detectors 42 have a triangular geometry and are located such that one side of the virtual wall detectors 42, its bottom side 42a, extends in a common ground plane, the combination of bottom sides 42a forming a polygon ground profile, while the other sides 42b,c of the virtual wall detectors 42 are connected to corresponding sides of adjacent virtual wall detectors 42, and the vertices 42d of the triangular shaped virtual wall detectors 42 that are opposite to the bottom sides 42a all coincide thus forming a pyramidal shaped virtual cover detector, covering a three-dimensional detection space. Preferably, at least a number of receivers are located at upwardly oriented sides of the virtual wall detectors 42, for forming a mesh or matrix of transmitter receivers pairs.

The pyramidal shaped virtual cover detector 41 can be applied for analyzing explosive characteristics of a detonating explosive 50 by measuring size, direction, speed and crossing location of explosive fragments travelling through virtual wall detectors 42 of the virtual cover detector 41, as an alternative to time consuming arena fragmentation tests. Preferably, the optical receivers 4 of the virtual wall detectors 42 are shielded from a location where the explosive 50 has been placed, so that there is no line of sight between the explosive and the receivers 4, thereby counteracting any disturbing effects of radiation and/or illumination by the exploding explosive on the detection of explosive fragments in the beam 3 propagating from a transmitter 2 towards a receiver 4 that is operationally optically coupled to said transmitter. The pyramidal shaped virtual cover detector 41 may include a single or a multiple number of shielding elements obstructing or at least attenuating transmission of optical beams or radiation from the location of the explosive 50 towards receivers 4 of the virtual cover detector 41.

It is noted that also a box-shaped virtual cover detector 1 having-rectangular shaped virtual wall detectors as described referring to Fig. 7 can be applied for analyzing explosive characteristics of a detonatingexplosive 50. It is noted that a box-shaped virtual cover detector having rectangular shaped virtual wall detectors, preferably defining a mesh or matrix of transmitter receiver pairs, e.g. as shown in Fig. 4, may be optimal in terms of effectiveness, efficiency and costs.

In the embodiment shown in Fig. 8, at least a majority of the optical receivers 4 is located at the bottom side 42a of the respective virtual wall detectors 42, while a shielding wall 43 is provided inside the pyramidal shaped virtual cover detector 41, between the location of the explosive 50 and the receivers 4 at the bottom side 42a of the respective virtual wall detectors 42. The shielding wall may be integrally formed or may be composed of a multiple number of shielding wall segments that are located adjacent each other, side by side, surrounding the location where the explosive 50 has been placed, e.g. at the center of the polygon ground profile formed by the bottom sides 42a of the virtual wall detectors 42. Alternatively or additionally, individual shielding elements can be provided near the individual receivers 4 shielding them against radiation and/or optical beams generated by the exploding explosive.

Advantageously, at least a number of the virtual wall detectors 42 of the pyramidal shaped virtual cover detector 41 have been implemented as virtual double wall detectors as described referring to Fig. 7 thereby enabling the virtual cover detector 1 to estimate the travelling direction and/or speed of explosive fragments moving from the three-dimensional detection space 20 or inner space of the pyramid outwardly, through the virtual double wall detectors.

Generally, during operation of the system 1, respective transmitters 2 are optically coupled to respective receivers 4, via receipt of the optical beams 3 transmitted by the transmitters 2 and evaluation of a code of the received optical beams 3, e.g. wavelength, modulation or other coded temporal or spectral variation of the received beams to check whether the code matches with a pre-determined code associated with the respective receivers 4. The detection unit is arranged for registering an interruption of optical beam receipt in the virtual beam detector. It is noted that a temporal coded transmission is more robust against hacking.

Upon detection that a single or multiple number of beams are interrupted, it is determined that an object is locally present in the optical path of the respective beams. Any interruption of an optical beam can be determined by verifying that a received power of the beam is below a predefined level. Also, a change of beam intensity can be monitored for determining an interruption, increasing sensitivity of the system. Based on interruption data, the detection unit 9 may estimate static and/or dynamic characteristics of said object causing the beam interruption or interruptions. In principle, the interruption data are available immediately, making real time object detection possible, locally or remotely.

As an example of dynamic characteristics of the detected object, location information of the object interrupting the beam or beams can be determined, such as a one-dimensional or two-dimensional location in a virtual wall detector. In this respect it is noted that a one-dimensional location in a virtual wall detector actually represents a two-dimensional location in three-dimensional space, while a two-dimensional location in a virtual wall detector represents a three-dimensional location in the virtual wall detector. Depending on the number, location and orientation of the interrupted optical beams, location information of the object can be found. As an example, when two interrupted beams cross each other, the object is expected to be present in or close to the crossing point of the interrupted beams.

Further, as an example of static characteristics of the detected object, size characteristics of the detected object can be determined, based upon the number of beams that are interrupted as a cluster. As an example, if a number of subsequent parallel beams are interrupted, it may be concluded that the detected object has a spatial extension as wide as a space occupied by said interrupted parallel beams. In principle, if a cluster of interrupted beams is separated from another cluster of interrupted beams by a single or multiple number of uninterrupted beams, it is concluded that at least two separate objects cross the virtual wall detector.

In case of a virtual double wall detector, further information can be determined, based on the interruption data. As an example, the detection unit 9 can be arranged for estimating a speed and/or a travel direction of an object passing through a front virtual wall detector 31 and a back virtual wall detector 32 arranged behind each other. In principle, an object speed can be determined by interrelating a distance between the crossing locations of the respective virtual wall detectors placed behind each other, and a crossing time period that has lapsed between interrupting a beam in the front virtual wall detector 31 and interrupting a beam in the back virtual wall detector 32. Further, by determining an optical path orientation between the crossing locations of the front and back virtual wall detectors 31, 32 a travel direction or angle of incidence of the detected object can be determined.

The above-mentioned virtual double wall detector can advantageously be used for detecting bullets, missiles and other hostile projectiles in a military context, especially for localizing from which direction an area is attacked.

Optionally, a low pass filter, a band pass filter or a high pass filter can be applied to interruption data e.g. such that slowly moving objects through or on the virtual wall detector, such as moving insects, are filtered out. Further, each transmitter receiver pair may be operated using a filter.

It is noted that a detection performance of a virtual wall detector depend on at least a density , extension and offsets of receivers on a side or array of the virtual wall. In general, when applying a high density of receivers and low offsets between them, relatively small objects traversing the wall can be detected. In principle, a maximum size or mesh size and/or minimum density of receivers can be determined based on a minimum size of objects that should be detected by the system 1. Also an accuracy in determining the orientation of the projectile path may be included. As an example, it may follow that a receiver size is at least 2.5 times larger than a minimum size of a projectile to be detected. Then, objects as small as 1 mm with velocities up to circa 5000 m/s can be detected. Further, a coding frequency has to be set above a minimum level to counteract that detection of a high speed object is missed, e.g. propagating through a beam in a zero pulse interval of a pulse coded beam. In addition, a double row of receivers, arranged behind each other, can be applied if it is undesired that subsequent receivers have a non-zero intermediate space therebetween. A second row may include receivers that have been shifted relative to receivers in a first row, over a distance that is at least the intermediate space between receivers in the first row, thus providing a full coverage of detectors along a receiver line.

It is noted that the transmitters and receivers can be arranged in an alternative way, not on a contour surrounding in a two-dimensional detection area. As an example, transmitters and corresponding receivers can be positioned in a three dimensional space such as a hall or room, at random, creating a three-dimensional beam configuration throughout a three-dimensional space to be protected. As an example, a cluster of transmitters can be located adjacent to each other while receivers, optically coupled to said transmitters via coding, can be located at remote locations somewhere in the three-dimensional space to be protected. In principle, the system is modular and can be extended with further clusters of transmitters and/or receivers.

Figure 9 shows a flow chart of a method according to the invention. The method 100 is used for detecting an object. The method comprises a step of providing 110 a multiple number of optical transmitters for transmitting optical beams, a step of providing 120 a multiple number of optical receivers for receiving the transmitted optical beams, and a step of registering 130 an interruption of receipt of a transmitted optical beam, wherein each receiver is operationally optically coupled to a corresponding transmitter such that each receiver and its corresponding transmitter form a virtual beam detector.

The method for detecting an object can be performed using dedicated hardware structures, such as FPGA and/or ASIC components. Otherwise, the method can also at least partially be performed using a computer program product comprising instructions for causing a processor of a computer system or a control unit, viz. included in a central or distributed detection unit, to perform the above described registering step, or at least a sub-step thereof. As an example, the evaluation of beam codes related to beams received by the receivers can be performed centrally at a single detection unit, or in a distributed manner by respective detection subunits connected to a single or a multiple number of receivers.

All steps can in principle be performed on a single processor. However, it is noted that at least one sub-step can be performed on a separate processor. A processor can be loaded with a specific software module. Dedicated software modules can be provided.

The invention is not restricted to the embodiments described herein. It will be understood that many variants are possible.

The optical beams that are transmitted by the transmitters may have a colour in the visible spectrum, e.g. for the purpose of prevention. However, the beams may have another wavelength, e.g. in the infrared or ultraviolet regime in order to make the system invisible and minimize a chance that third parties discover operation of the system.

When the distance between the transmitter and the operationally optically coupled receiver is relatively large, the transmitter may include a laser with limited divergence to reduce optical losses, e.g. by providing optics at the laser such that the beam, after passing through the optics, slightly diverges. Generally, laser technology is applicable if the system is sufficiently rigid such that a modification of position and/or orientation of transmitters and receivers does not interrupt an optical connection of an optically coupled pair of transmitter and receiver. Further, an aperture of the transmitters and receivers can be modified using optics including lenses and/or cylinders.

It is noted that the system according to the invention can be combined with other measurement techniques, such as acoustic systems for determining a propagation direction of detected objects.

These and other embodiments will be apparent for the person skilled in the art and are considered to fall within the scope of the invention as defined in the following claims. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments. However, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Claims (17)

An object detection system, comprising a plurality of optical transmitters for transmitting optical beams and a plurality of optical receivers for receiving the transmitted optical beams, further comprising a detection unit adapted to record a interruption of receipt of a transmitted optical bundle, wherein each receiver is optically coupled during operation to a corresponding transmitter such that each receiver and the corresponding transmitter form a virtual bundle detector. The system of claim 1, wherein the detection unit is adapted to record an interruption of optical beam reception in the virtual beam detector. The system of claim 1 or 2, wherein a plurality of receivers are optically coupled to a specific transmitter during operation. A system according to any one of the preceding claims, wherein a plurality of transmitters is optically coupled to a specific receiver during operation. A system according to any one of the preceding claims, wherein each transmitter is adapted to send an optical bundle that is uniquely coded to optical bundles transmitted by other transmitters. The system of claim 5, wherein each receiver is arranged to optically couple during operation to a transmitter that transmits a bundle with a code corresponding to a predetermined code. System as claimed in any of the foregoing claims, comprising a substantially elongated support structure, wherein groups of transmitters and / or groups of receivers are at least mutually different levels in the elongated support structure, preferably in an alternating manner. A system according to claim 7, wherein a group of transmitters and / or a group of receivers are arranged at a specific level, in the elongated support structure, such that they form vertices of a polygon, preferably a regular polygon. 9. System as claimed in claim 8, wherein in a top view of the elongated support structure, corner points of a next group are situated substantially halfway between circumferentially adjacent corner points of a previous group. A system according to any one of the preceding claims, wherein the transmitters and receivers are arranged along a detection contour extending in a common plane, and surround or enclose a two-dimensional detection area to form a virtual wall detector. The system of claim 10, further comprising a reflection line that delimits the two-dimensional detection area. 12. System as claimed in any of the foregoing claims 10-11, wherein the detection unit is adapted to estimate a location and / or size of an object in the detection area that causes at least one beam interruption in a plurality of virtual beam detectors of the virtual wall detector. A system according to any of the preceding claims 10-12, comprising a plurality of virtual wall detectors arranged side by side that surround a three-dimensional detection space to form a virtual cover detector. A system according to any one of the preceding claims 10-12, comprising a plurality of virtual wall detectors arranged one behind the other to form a virtual double wall detector. The system of claim 14, wherein the detection unit is adapted to estimate a speed and / or propagation direction of an object passing through virtual wall detectors arranged one behind the other. Method for detecting an object, comprising the steps of: - providing a plurality of optical transmitters for transmitting optical beams; - providing a plurality of optical receivers for receiving the transmitted optical bundles; - registering an interruption of receipt of a transmitted optical bundle, wherein each receiver is optically coupled during operation to a corresponding transmitter such that each receiver and the corresponding transmitter form a virtual beam detector. A computer program product for detecting an object, the computer program product comprising computer readable code which causes a processor to perform the step of registering an interruption of reception of a transmitted optical bundle, the bundle being transmitted by a transmitter of a a plurality of optical transmitters, and receiver through at least one receiver of a plurality of optical receivers, and wherein each receiver is optically coupled during operation to a corresponding transmitter such that each receiver and the corresponding transmitter form a virtual beam detector.