Lighting control system

Abstract

To avoid packet collisions in wireless mesh networks. [Solution] The lighting control system according to the embodiment comprises a plurality of lighting fixtures forming a wireless mesh network and a control device for controlling the lighting fixtures. The lighting fixtures transmit status packets indicating their own status information to the wireless mesh network at a transmission time determined by the control device, and transmit received packets received from other lighting fixtures to the wireless mesh network according to the timing of receipt.

Description

Technical Field

[0001] The present invention relates to a lighting control system.

Background Art

[0002] Conventionally, there is a lighting control system including a plurality of lighting fixtures, sensors, and the like. For example, in a lighting control system, a wireless mesh network is formed by a plurality of lighting fixtures and sensors, and signals transmitted from the outside are transferred to each other on the wireless mesh network (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the prior art, packets transmitted from each lighting fixture to the wireless mesh network may collide.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a lighting control system capable of avoiding packet collisions in a wireless mesh network.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, a lighting control system according to the present invention includes a plurality of lighting fixtures forming a wireless mesh network and a control device for controlling the lighting fixtures. The lighting fixture transmits a status packet indicating the status information of its own device to the wireless mesh network at a transmission time determined by the control device, and transmits the received packet received from another lighting fixture to the wireless mesh network according to the timing of reception. [Effects of the Invention]

[0007] According to the present invention, packet collisions in a wireless mesh network can be avoided. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a diagram showing an overview of the lighting control system according to an embodiment. [Figure 2] Figure 2 shows an example of a distributed control system configuration. [Figure 3] Figure 3 is a block diagram of the area controller according to this embodiment. [Figure 4] Figure 4 is a block diagram of a lighting fixture according to an embodiment. [Figure 5] Figure 5 is an explanatory diagram of the synchronization process according to the embodiment. [Figure 6] Figure 6 is an explanatory diagram of the status packet transmission process according to the embodiment. [Figure 7] Figure 7 is an explanatory diagram of the transmission process of a state packet according to the embodiment. [Figure 8] Figure 8 is a flowchart showing the processing procedure executed by the area controller according to this embodiment. [Figure 9] Figure 9 is a flowchart showing the processing procedure performed by the lighting fixture according to the embodiment. [Modes for carrying out the invention]

[0009] The lighting control system S according to the embodiment described below comprises a plurality of lighting fixtures 10 that form a mesh network N (an example of a wireless mesh network) and an area controller 1 (an example of a control device). The lighting fixtures 10 transmit status packets indicating their own status information to the mesh network N (an example of a wireless mesh network) at a transmission time determined by the area controller 1 (an example of a control device), and transmit received packets received from other lighting fixtures 10 to the mesh network N (an example of a wireless mesh network) according to the timing of receipt.

[0010] Furthermore, the lighting fixture 10 according to the embodiment described below retransmits the status packet after a random time has elapsed since the initial transmission.

[0011] Furthermore, the area controller 1 (an example of a control device) according to the embodiment described below transmits synchronization packets for time synchronization of multiple lighting fixtures 10 to a mesh network N (an example of a wireless mesh network), and when a lighting fixture 10 relays a synchronization packet to another lighting fixture 10, it corrects the synchronization packet by the relay processing time before transmitting it.

[0012] Furthermore, the area controller 1 (an example of a control device) according to the embodiment described below sets non-overlapping transmission times for each lighting fixture 10.

[0013] Furthermore, the area controller 1 (an example of a control device) according to the embodiment described below sets non-overlapping transmission times for each group including multiple lighting fixtures 10, and the lighting fixtures 10 transmit status packets within the transmission time set for each group.

[0014] Furthermore, the lighting fixture 10 according to the embodiment described below sends a status packet to the mesh network N (an example of a wireless mesh network) at the start of the transmission time set for each group, and after sending the status packet, it retransmits the status packet after a random time has elapsed.

[0015] In addition, the lighting fixture 10 according to the embodiment described below receives a received packet and transmits the received packet to the mesh network N (an example of a wireless mesh network) after a random time has elapsed.

[0016] (Embodiment) Hereinafter, embodiments of the present invention will be described based on the drawings. Note that each of the embodiments shown below does not limit the technology disclosed by the present invention. In addition, the same parts in each embodiment are denoted by the same reference numerals, and overlapping descriptions are omitted.

[0017] First, the outline of the lighting control system according to the embodiment will be described using FIG. 1. FIG. 1 is a diagram showing the outline of the lighting control system according to the embodiment. As shown in FIG. 1, the lighting control system S includes an area controller 1 and a plurality of distributed control systems 100.

[0018] The area controller 1 is the master unit of the plurality of distributed control systems 100 and is a control device that controls each distributed control system 100. Note that the area controller 1 corresponds to an example of a control device that controls a lighting fixture. Note that the control device may be a device provided in the distributed control system 100.

[0019] For example, the area controller 1 individually controls each distributed control system 100 by transmitting control information to each distributed control system 100. In addition, the area controller 1 acquires the state information transmitted from each distributed control system 100 at a predetermined cycle and can grasp the current state of each distributed control system 100.

[0020] In the present disclosure, the state in which the area controller 1 controls each distributed control system 100 is described as centralized control, and the state in which each distributed control system 100 controls independently is described as distributed control.

[0021] The lighting control system S according to the embodiment is a system that can operate by switching between centralized control and distributed control.

[0022] Each distributed control system 100 is a system that includes lighting fixtures. Here, a specific example of the distributed control system 100 according to the embodiment will be described using Figure 2. Figure 2 is a diagram showing an example of the configuration of the distributed control system 100.

[0023] As shown in Figure 2, the distributed control system 100 consists of lighting fixtures 10, switches 20, a scheduler 30, sensors 40, and terminal devices 50, etc. Note that in the example shown in Figure 2, one of each device is shown for illustrative purposes, but any number of each device can be included.

[0024] Furthermore, as shown in Figure 2, each device constituting the distributed control system 100 forms a mesh network N. The mesh network N is a network formed by wireless communication conforming to the Bluetooth® or BLE (Bluetooth® Low Energy) communication standards.

[0025] Each device connected to the mesh network N can receive various instructions and other signals transmitted from external devices, such as the area controller 1, by forwarding these instructions to the mesh network N.

[0026] The lighting fixture 10 is a predetermined lighting device such as a base light, ceiling light, downlight, or spotlight. The lighting fixture 10 also has a wireless communication function and communicates with other devices located within the wireless communication range via the mesh network N.

[0027] Sensor 40 detects various types of information. Sensor 40 also has a wireless communication function and communicates with other devices located within wireless communication range via the mesh network N. For example, sensor 40 may include an imaging unit that includes a CMOS (Complementary Metal Oxide Semiconductor) image sensor or a CCD (Charge Coupled Device) image sensor, and may function as a human presence sensor or an illuminance sensor. When sensor 40 functions as a human presence sensor, it detects whether or not a person is present in the detection range from the image captured by the imaging unit, and transmits the detection result to the lighting fixture 10 via the mesh network N. When sensor 40 is an illuminance sensor, it detects whether or not a person is present in the detection range from the image captured by the imaging unit, and transmits the detection result to the lighting fixture 10 via a predetermined network.

[0028] The scheduler 30 controls other devices such as the lighting fixture 10 and the sensor 40. The scheduler 30 outputs predetermined control signals to control the other devices such as the lighting fixture 10 and the sensor 40 at timings set by the user of the terminal device 50 (for example, a system administrator). The scheduler 30 also has a wireless communication function and may communicate with other devices located within the wireless communication range via the mesh network N.

[0029] Switch 20 is a device that outputs a predetermined control signal to a pre-assigned lighting fixture 10. Switch 20 also has a wireless communication function and may communicate with other devices located within wireless communication range via a mesh network N.

[0030] The terminal device 50 is an information processing terminal that has various functions such as communication, display, and web browsing functions, and performs information processing according to the embodiment. The terminal device 50 is also equipped with a dedicated application program that provides various functions for realizing the information processing according to the embodiment. For example, a user of the terminal device 50 can perform setting operations on other devices such as lighting fixtures 10 through functions provided by the dedicated application. The terminal device 50 can be implemented using a smart device (smartphone or tablet), a PDA, or a desktop or laptop personal computer.

[0031] Next, an example of the configuration of the area controller 1 according to the embodiment will be described using Figure 3. Figure 3 is a block diagram of the area controller 1 according to the embodiment. As shown in Figure 3, the area controller 1 has a time management unit 3, a storage unit 4, and a control unit 5.

[0032] The time management unit 3 is composed of, for example, a counter circuit that increases by 1 at a fixed period (e.g., 1 usec or 1 msec period). The time of the control unit 5, which will be described later, generates the reference time for each lighting fixture 10. The control unit 5 reads the value of the counter managed by the time management unit 3 at a fixed period (e.g., 30 seconds or 1 minute), generates a packet containing that counter value, and transmits it to each distributed control system 100 via the communication unit 2.

[0033] The storage unit 4 is implemented using, for example, semiconductor memory elements such as RAM (Random Access Memory) or flash memory, or storage devices such as hard disks or optical discs. In the example shown in Figure 3, the storage unit 4 stores device information 4a.

[0034] Equipment information 4a is information about each device that constitutes the distributed control system 100. In this disclosure, equipment information 4a includes status information for each device.

[0035] The control unit 5 is a controller, and is realized by various programs stored in the memory device inside the area controller 1 being executed using RAM as the working area by a CPU (Central Processing Unit) or MPU (Micro Processing Unit), for example. As shown in Figure 3, the control unit 5 has a receiving unit 5a, a processing unit 5b, and a transmitting unit 5c, and realizes or executes the information processing functions and operations described below.

[0036] The receiving unit 5a receives various information from each device constituting the distributed control system 100 via the mesh network N. For example, the receiving unit 5a receives status packets from each device indicating the status of each device.

[0037] The processing unit 5b performs various processes related to the control of each device that constitutes the distributed control system 100. For example, the processing unit 5b generates various packets for controlling each device and analyzes status packets transmitted from each device.

[0038] The transmitting unit 5c transmits various packets to each device constituting the distributed control system 100 via the mesh network N. The transmitting unit 5c transmits synchronization packets, etc., to synchronize the time of each device. The receiving unit 5a and the transmitting unit 5c may be provided separately from the control unit 5. The area controller 1 may also have a communication unit that can communicate with a higher-level device via Ethernet (registered trademark), etc.

[0039] Next, an example of the configuration of the lighting fixture 10 according to the embodiment will be described using Figure 4. Figure 4 is a block diagram of the lighting fixture 10 according to the embodiment. As shown in Figure 4, the lighting fixture 10 according to the embodiment comprises a light-emitting unit 12, a time management unit 13, a storage unit 14, and a control unit 15.

[0040] The light-emitting unit 12 illuminates a predetermined area. For example, the light-emitting unit 12's state (on, off, and intensity when lit) is controlled by the control unit 15.

[0041] The time management unit 13 is composed of, for example, a counter circuit that increases by 1 at a fixed period (for example, a period of 1 usec or 1 msec).

[0042] The storage unit 14 is implemented by, for example, a semiconductor memory element such as RAM or flash memory, or a storage device such as a hard disk or optical disc. In the example shown in Figure 4, the storage unit 14 stores packet information 141. The packet information 141 is information about packets generated by the control unit 15. In this disclosure, the packet information includes state packets and received packets, which will be described later.

[0043] The control unit 15 is a controller, and is realized, for example, by a CPU or MPU executing various programs stored in the storage device inside the lighting fixture 10 using RAM as the working area. As shown in Figure 4, the control unit 15 has a receiving unit 151, a generating unit 152, and a transmitting unit 153, and realizes or executes the information processing functions and operations described below.

[0044] The receiving unit 151 receives various types of information through the mesh network N. For example, the receiving unit 151 receives control instructions from the area controller 1 and received packets transmitted from other devices through the mesh network N.

[0045] The generation unit 152 generates status packets that indicate the status of the device. For example, the generation unit 152 generates status packets at the timing specified by the time management unit 13.

[0046] The transmitting unit 153 transmits various information through the mesh network N. For example, the transmitting unit 153 transmits status packets generated by the generation unit 152 to the area controller 1 through the mesh network N.

[0047] Furthermore, the transmitting unit 153 transmits received packets, which are status packets of other devices, to the area controller 1 and other devices via the mesh network N. Note that the receiving unit 151 and the transmitting unit 153 may be provided separately from the control unit 15. In addition, the lighting fixture 10 may have a communication unit that can communicate with devices outside the distributed control system 100 via Ethernet or the like.

[0048] In this disclosure, the transmitting unit 153 transmits a status packet indicating the status information of its own device to the mesh network N at a transmission time determined by the area controller 1, and transmits received packets received from other lighting fixtures 10 to the mesh network N according to the timing of their receipt.

[0049] Here, we will explain the processing by the lighting control system S according to the embodiment using Figures 5 to 7. First, we will explain the time synchronization process of the area controller 1 and the lighting fixture 10 using Figure 5.

[0050] Figure 5 is an explanatory diagram of the synchronization process according to the embodiment. The horizontal axis in Figure 5 represents the passage of time. Furthermore, in the following, it is assumed that packets transmitted by area controller 1 pass through lighting fixture #1 and lighting fixture #2 before reaching lighting fixture #3, and that packets transmitted by area controller 1 pass through lighting fixture #1 before reaching lighting fixture #2.

[0051] As shown in Figure 5, the area controller 1 sends a synchronization packet Pktt to the mesh network N at time t1 for time synchronization. The synchronization packet is a packet that indicates the counter value of the time management unit 3 of the area controller 1.

[0052] For example, lighting fixture #1 receives a synchronization packet Pktt at time t1 and synchronizes the counter value of its own time management unit 13 with the counter value of the time management unit 3 of area controller 1 based on the synchronization packet Pktt.

[0053] Next, lighting fixture #1 generates a synchronization packet Pktta and transmits it to the mesh network N at time t2. For example, the counter value of synchronization packet Pktta is the counter value of synchronization packet Pktt corrected by the relay processing time of synchronization packet Pktt. That is, in the example shown in Figure 5, there is a delay of time t1 to time t2 between when lighting fixture #1 receives synchronization packet Pktt and when it transmits synchronization packet Pktta. Therefore, lighting fixture #1 generates a synchronization packet Pktta with the counter value of synchronization packet Pktt corrected by time t1 to time t2 and transmits it to the mesh network N.

[0054] Next, at time t2, lighting fixture #2 receives the synchronization packet Pktta and synchronizes the counter value of its own time management unit 13 with the counter value of the time management unit 3 of area controller 1.

[0055] Then, lighting fixture #2, similar to lighting fixture #1, generates a synchronous packet Pkttb from the received synchronous packet Pktta, corrected by the relay processing time, and transmits it to the mesh network N at time t3.

[0056] As a result, lighting fixture #3 can receive the synchronization packet Pkttb at time t3, and based on the received synchronization packet Pkttb, synchronize the counter value of its own time management unit 13 with the counter value of the time management unit 3 of area controller 1.

[0057] Thus, in this disclosure, when forwarding the synchronous packet Pktt, each device performs a correction equal to the relay processing time. This enables accurate time synchronization of each device.

[0058] Next, the transmission process of status packets by each lighting fixture 10 will be explained using Figure 6. Figure 6 is an explanatory diagram of the transmission process of status packets according to the embodiment. In Figure 6, as with Figure 5, lighting fixture #1 is assumed to act as a relay when sending and receiving data between the area controller 1 and lighting fixture #2.

[0059] As shown in Figure 6, this disclosure sets a transmission time for sending status packets for each lighting fixture 10. In the example shown in Figure 6, the transmission time for lighting fixture #1 is period a from time t11 to time t14, and the transmission time for lighting fixture #2 is period b from time t16 to time t19. In other words, in the example in Figure 6, non-overlapping transmission times are set for each lighting fixture 10. Furthermore, the periods from time t10 to time t11, time t14 to time t15, and time t15 to time t16 are margins that take into account the time synchronization error of each lighting fixture 10.

[0060] For example, the area controller 1 determines the transmission time for each device based on each lighting fixture 10 and other devices that make up the distributed control system 100. As shown in Figure 6, lighting fixture #1 generates a packet Pa1 indicating the status of its own device at time t11 when period a, which is its own transmission time, begins.

[0061] The packet Pa1 generated by lighting fixture #1 is sent to the mesh network N as a status packet Ptk1 at time t12, and area controller 1 receives the status packet Ptk1 from lighting fixture #1 at time t12.

[0062] Furthermore, lighting fixture #1 retransmits the status packet Ptk1 after a random time has elapsed from the time t12 when it initially sent the status packet Ptk1. In the example in Figure 6, lighting fixture #1 retransmits the status packet Ptk1 at time t13, after a random retransmission time Nti1 has elapsed from the time t12 when it initially sent the status packet Ptk1.

[0063] Next, we will explain the process of sending status packets by lighting fixture #2. Lighting fixture #2 generates a packet Pa2 indicating its own status at time t16, when period b, which is the transmission time of its own device, begins.

[0064] Packet Pa2 generated by lighting fixture #2 is sent to mesh network N as status packet Ptk2 at time t17, and lighting fixture #1 receives status packet Ptk2 at time t17. Note that the status packet Ptk2 received by lighting fixture #1 corresponds to an example of a received packet.

[0065] Lighting fixture #1 forwards state packet Ptk2 as state packet Ptk2_r1 to mesh network N after a random time has elapsed since it received state packet Ptk2 at time t17.

[0066] In the example shown in Figure 6, lighting fixture #1 forwards the state packet Ptk2 as state packet Ptk2_r1 to the mesh network N at time t18, after a forwarding random time trand1 has elapsed from time t17, when it received the state packet Ptk2.

[0067] Furthermore, lighting fixture #2 retransmits the status packet Ptk2 at time t19, after a random retransmission time Nti2 has elapsed from time t17, when it sent the status packet Ptk2.

[0068] Thus, in this disclosure, collisions of status packets for each lighting fixture 10 can be avoided by setting different transmission times for each lighting fixture 10. In addition, each lighting fixture 10 retransmits a status packet after a random time has elapsed, and a device that relays status packets forwards it after a random time has elapsed since receiving a status packet from another device.

[0069] In this way, since both the device that sends the status packet and the device that relays the status packet utilize the mesh network N after a random time interval, the timing of each device's use of the mesh network N can be appropriately staggered, thus avoiding packet collisions.

[0070] At time t13, area controller 1 will receive status packet Pkt1 again, which was retransmitted by lighting fixture #1. However, since it had already received status packet Pkt1 at time t12, the status packet Pkt1 received at time t13 will be discarded. Similarly, at time t19, lighting fixture #1 will receive status packet Pkt2 from lighting fixture #2 again. However, it will discard the status packet Pkt2 received at time t19.

[0071] Next, using Figure 7, we will explain the transmission process of status packets when a transmission time is set for each group containing multiple lighting fixtures 10. Figure 7 is an explanatory diagram of the transmission process of status packets according to an embodiment.

[0072] As shown in Figure 7, assume that a period a is set for the transmission time of status packets for both lighting fixture #1 and lighting fixture #2, from time t21 to time t27. For example, in this case, lighting fixture #1 and lighting fixture #2 generate packet Pa1 and packet Pa2, respectively, at time t21 when period a begins.

[0073] Next, lighting fixture #1 and lighting fixture #2 each send their respective state packets Pkt1 and Pkt2 to the mesh network N after a random time has elapsed from time t21.

[0074] In the example shown in Figure 7, lighting fixture #1 sends status packet Pkt1 at time t22, after a random transmission time trandN1 has elapsed from time t21, and lighting fixture #2 sends status packet Pkt2 at time t23, after a random transmission time trandN2 has elapsed from time t21.

[0075] Furthermore, when lighting fixture #1 receives the status packet Pkt2 sent by lighting fixture #2 at time t23, it forwards the status packet Pkt2 as status packet Pkt2_r1 after a random time has elapsed. The example shown in Figure 7 illustrates the case where lighting fixture #1 forwards the status packet Pkt2 as status packet Pkt2_r1 at time t26, after a random forwarding time trandR1 has elapsed from time t23, when it received the status packet Pkt2 sent by lighting fixture #2.

[0076] In this way, even if overlapping transmission times are set for multiple devices, the timing at which each device utilizes the mesh network N can be appropriately staggered by setting random transmission times and random transfer times.

[0077] Next, the processing procedure executed by the area controller 1 according to the embodiment will be described using Figure 8. Figure 8 is a flowchart showing the processing procedure executed by the area controller 1 according to the embodiment.

[0078] As shown in Figure 8, first, the area controller 1 sets the transmission time for each device that constitutes the distributed control system 100 to send status packets (step S101), and then notifies each device of its transmission time (step S102).

[0079] Then, the area controller 1 receives status packets from each device within the transmission time set for each device (step S103) and terminates processing.

[0080] Next, the processing procedure performed by the lighting fixture 10 according to the embodiment will be described using Figure 9. Figure 9 is a flowchart showing the processing procedure performed by the lighting fixture 10 according to the embodiment.

[0081] As shown in Figure 9, the lighting fixture 10 first determines whether or not it is time to send a status packet (step S201). If the lighting fixture 10 determines that it is time to send a status packet (step S201; Yes), it sends the status packet to the mesh network N (step S202).

[0082] Furthermore, if the lighting fixture 10 determines in step S201 that it is not time to send a status packet (step S201; No), it proceeds to the process in step S203. Next, the lighting fixture 10 determines whether or not there is a received packet to forward (step S203).

[0083] If the lighting fixture 10 determines that there is a received packet to forward (step S203; Yes), it forwards the received packet to the mesh network N (step S204) and terminates processing.

[0084] Furthermore, if the lighting fixture 10 determines in step S203 that there are no received packets to transfer (step S203; No), it terminates processing.

[0085] As described above, the lighting control system S according to the embodiment comprises a plurality of lighting fixtures 10 that form a mesh network N (an example of a wireless mesh network) and an area controller 1 (an example of a control device). The lighting fixtures 10 transmit status packets indicating their own status information to the mesh network N (an example of a wireless mesh network) at a transmission time determined by the area controller 1 (an example of a control device), and transmit received packets received from other lighting fixtures 10 to the mesh network N (an example of a wireless mesh network) according to the timing of receipt.

[0086] Therefore, according to the lighting control system S of this embodiment, packet collisions in a wireless mesh network can be avoided.

[0087] While embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0088] 1 Area Controller 3 Time management department 4 Storage section 4a Device information 5. Control Unit 5a Receiving section 5b Processing Unit 5c Transmitter 10 Lighting fixtures 12 Light-emitting part 13 Time management department 14 Storage section 15 Control Unit 20 switches 30 Scheduler 40 sensors 50 Terminal devices 100 Distributed Control Systems 151 Receiving Unit 152 Generation part 153 Transmitter S Lighting Control System

Claims

1. Multiple lighting fixtures forming a wireless mesh network; A control device for controlling the aforementioned lighting fixture; It is equipped with, The aforementioned lighting fixture is The device transmits a status packet indicating its own status information to the wireless mesh network at the transmission time determined by the control device. The system transmits received packets from other lighting fixtures to the wireless mesh network according to the timing of their receipt. Lighting control system.

2. The aforementioned lighting fixture is After sending the status packet, the status packet is resent after a random time has elapsed. The lighting control system according to claim 1.

3. The control device is A synchronization packet for time synchronization of multiple lighting fixtures is sent to the wireless mesh network. The aforementioned lighting fixture is When relaying the aforementioned synchronization packet to another lighting fixture, the synchronization packet is corrected by the relay processing time before transmission. The lighting control system according to claim 1.

4. The control device is Set the transmission time for each of the aforementioned lighting fixtures so that they do not overlap. The lighting control system according to claim 1.

5. The control device is Set non-overlapping transmission times for each group containing multiple lighting fixtures. The aforementioned lighting fixture is The status packets are transmitted within the transmission time set for each group. The lighting control system according to claim 1.

6. The aforementioned lighting fixture is After the start of the transmission time set for each group, the status packet is sent to the wireless mesh network. After sending the aforementioned status packet, the status packet is resent after a random time has elapsed. The lighting control system according to claim 5.

7. The aforementioned lighting fixture is After receiving the aforementioned received packet, the received packet is transmitted to the wireless mesh network after a random time has elapsed. The lighting control system according to claim 1.

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