FIELD OF THE INVENTION

The present invention relates in general to sensor systems for dispensers. Particularly, the present invention relates to dispensers such as soap dispensers, paper towel dispensers, air freshener dispensers, used in the toilet rooms of large buildings, including office buildings, hotels, airports, etc. The present invention will be specifically explained for dispensers of the above type, but the application of the inventive concept is not limited to these dispensers; conceivably, the present invention can also be applied with dispensers for snacks, cigarettes, etc. BACKGROUND OF THE INVENTION

Understandably, a dispenser should always be in a filled condition. If for instance a soap dispenser in a public toilet room gets empty, the guests can not wash their hands in a hygienic manner any more, and if the towel dispenser gets empty, the guests can not dry their hands. However, the costs of maintaining the dispensers is an important issue. It is for instance possible that maintenance personnel regularly checks upon all dispensers, but this may mean that the

dispensers are filled up while that was not yet necessary if the personnel checks too frequently, or that a dispenser is already empty if the personnel does not check frequently enough. With a view to increased efficiency, it is desirable that the maintenance personnel is only directed to those dispensers that need refilling in the near future. For this purpose, it is possible to equip each dispenser with a level sensor, which senses the level of the dispenser's contents and transmits a sensor signal to a central processing device, typically a managing computer.

It is further desirable that the sensing system, i.e. the combination of central processing device and the several sensors, is as low-cost as possible. Consequently, the communication between sensor and the central processing device, hereinafter simply indicated as "processor", is preferred to be wireless, because arranging a wired network is costly. Likewise, the sensors should be capable of operating without connection to mains, because arranging a power grid for the sensors is expensive.

Further, it is desirable that the sensors can be implemented as small add-on devices that can be added to existing dispensers.

SUMMARY OF THE INVENTION The above considerations lead towards a desirable implementation as self- contained module, the module containing the functionalities of powering, sensing and transmitting.

In an obvious implementation, such module would be battery-powered, and the sensor would be an active sensor for actively determining a value of a measuring parameter, for instance a level of liquid in a container (soap) or the height of a stack of items (paper towels), or the weight of the supply to be measured. However, such an approach would inevitably involve the need to also monitor the status of the battery.

The invention aims to provide a simple sensing system that does not require the use of batteries in the sensing modules.

To this end, the sensing according to the invention is based on the use of passive RFID tags. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of the present invention will be further explained by the following description with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which:

figure 1 schematically illustrates an RFID communication system;

figure 2 schematically illustrates an example of a container with a sensing system proposed by the present invention;

figure 3A is a graph of signal strength versus supply level;

figure 3B is a graph of signal strength versus supply level;

figure 4 schematically illustrates an example of a dispenser with a sensing system proposed by the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 schematically shows the essential components of an RFID

communication system 1 , i.e. an RFID transponder or tag 10 and an RFID reader 20. Since these systems are commonly known, the following explanation will be kept brief. The tag 10 comprises a chip 1 1 and an antenna 12, but does not comprise any battery. The reader 20 is capable of transmitting a radio frequent (RF) signal for interrogating the tag 10. When this interrogation signal is received by the tag 10, it will derive power from the received RF signal, and this power is used by the tag 10 to transmit an RF response signal, which contains a unique ID code identifying the specific tag. The reader 20 receives the coded response signal, and is capable of recognizing the ID code contained therein (for instance because the reader 20 contains a database of ID codes). Such passive RFID tag is typically used for recognizing and/or following mobile objects, for instance suitcases in a luggage handling system, parcels in a mail handling system, shoppings in a self-service shop. Basically, they only respond by "calling" their ID code, and they are not provided with any measuring facilities. Nevertheless, according to the inventive concept of the present invention, such simple passive RFID tag can be used in a sensing system.

Figure 2 schematically illustrates the inventive sensing system proposed by the present invention, generally indicated at 100. A container 5 contains a supply of consumable substance 2, for instance liquid soap. The container 1 communicates with a dispenser output not shows for sake of simplicity. The container 5 is provided with a plurality of passive RFID tags 10, which are individually distinguished by the addition of characters A, B, C, etc. The different RFID tags are located at mutually different heights, preferably above each other. The system 100 comprises supply- dependent signal interfering means, generally indicated at 110. The effect of the supply-dependent signal interfering means 110 is to influence the RF signal between the RFID reader 20 and a tag 10 as a function of the supply level. Figure 3A is a graph illustrating this effect. The horizontal axis represents the supply level (arbitrary units), while the vertical axis represents RF signal magnitude (arbitrary units) as received by a tag. When the supply is zero (empty), the signal magnitude is at a maximum MAX. With rising supply level, the signal magnitude remains constant until the supply level reaches a first level L1. With still increasing level, the signal strength reduces until the supply level reaches a second level L2. With further increasing supply level, the signal magnitude remains constant at this minimum level MIN, which may be zero but this is not essential. What is essential is that the RFID tag 10 has a response threshold TH: if the RF interrogation signal as received by the tag has a magnitude higer than the threshold TH, the tag will respond, but the tag will not respond if the RF interrogation signal has a magnitude lower than the threshold TH.

In figure 3A, it can be seen that the signal threshold TH is reached at a supply level Lx. As long as the supply level is lower than Lx, the RF signal as received by the tag is strong enough and the tag 10 will respond. When the supply level is higher than Tx, the RF signal as received by the tag is too weak and the tag 10 will not respond. Conversely, for the RFID reader 20 this means that if the reader does receive a response signal it knows that the supply level is lower than Lx. Not receiving a response signal may be interpreted as indicating that the supply level is higher than Lx, but it is to be noted that the tag may also be defective.

Thus, the tag 10 acts as a binary sensor, capable of issuing a binary response signal (yes/no) depending on whether or not a certain level is exceeded. Figure 3B is a similar graph illustrating an implementation where the relationship between tag response and supply level is reversed: low supply level corresponds to low signal strength while high supply corresponds to high signal strength.

The system can be implemented in many ways. The RFID reader 20 may be a hand-held or mobile apparatus, for service personnel to carry with them. But the reader may also be arranged in a fixed location, for instance in/above the ceiling of washing room or toilet room, capable of communicating with the tags of a plurality of dispensers, and coupled to a central controller via a wired or wireless network. Based on the information received from the several readers located within a building, the controller may issue a work program for maintenance personnel.

The supply-dependent signal interfering means 110 may be implemented in many ways. In the simplest embodiment, the consumable substance itself interferes with the RF signal by reducing the magnitude thereof. Best results are obtained when the substance is physically positioned between the tag 10 and the reader 20. It may be advantageous to have a metal shielding plate 120 positioned on the opposite side of the tag 10, so that the tag 10 is between the plate 120 and the substance 2, so that the RF signal can not bypass the substance 2 and reach the tag 10 from the opposite side but must pass through the substance 2 for being able to reach the tag.

As explained in the above, one tag 10 suffices to be able to make a distinction [more than Lx] / [less than Lx]. The precise values of L1 , L2 and Lx will, among others, depend on the physical size of the tag and on the location where the tag is positioned. The central controller 30 may issue a filling instruction when it appears that the supply level has dropped below Lx.

A more refined sensing is possible if the supply of substance 2 is provided with more than one tag, the different tags being associated with different threshold levels Lx: figure 2 illustrates an implementation with three tags 10A, 10B, 10C arranged above each other. If the container 1 is fully filled, the reader 20 will receive no response signals when it sends its interrogation signal. If the supply level drops below the threshold level Lx of the uppermost tag 10A, the reader 20 will receive a response signal only containing the ID code of the uppermost tag 10A: this is the situation shown in the figure. If the supply level drops below the threshold level of the second tag 10B, the reader 20 will receive a response signal containing the ID codes of the uppermost tag 10A and the second tag 10B. If the supply level drops below the threshold level of the lowermost tag 10C, the reader 20 will receive a response signal containing the ID codes of all three tags. The central controller 30, which knows which ID codes correspond to which tags at which containers, is now capable of monitoring the consumption of the substance 2 and may even predict when it is likely that the container 1 needs to be refilled. From this prediction, the controller 30 may decide to have the container filled during the next routine maintenance round, or to wait.

In the embodiment described above, the substance 2 itself acts directly as supply-dependent signal interfering means 1 10. Whether this is possible will depend among others on the physical properties of the substance (inherent RF

characteristics) and on the shape of the supply. For instance, when monitoring a supply of toilet paper, it may be difficult to use the paper itself as supply-dependent signal interfering means. Figure 4 illustrates a solution to this problem. The

consumable substance 2 is shown as a paper roll mounted in a housing 3. The supply-dependent signal interfering means 1 10 comprise an actuator 140 arranged movable within the housing 3, for instance by being hinged to the housing, as shown. The actuator 140 is always contacting the outer circumference of the paper roll 2, for instance by being biased by gravity, as shown. Alternatively, the actuator could be biased by a spring or the like. Again, the system 100 comprises at least one RFID tag 10 mounted in the housing 3, but preferably two or more RFID tags 10 mounted above each other. The actuator 140, which can be made of any suitable material, carries a shield 141 which is preferably made of metal. The arrangement of the actuator and the shield is such that the shield is positioned close to the RFID tags. With consumption of the toilet paper, the diameter of the paper roll 2 decreases, the actuator 140 moves, and the shield 141 travels along the series of (at least one) RFID tags, covering or releasing specific tags depending on its position and hence on the actual diameter of the paper roll 2. So, also in this embodiment, a tag does or does not respond to the interrogation signal depending on the actual diameter of the paper roll 2. It is noted that in the above it is assumed that the RFID tag only has two modes of operating: either it does respond to the interrogation signal or it does not. It may also be that there is a transition region where the response signal grows weaker with decreasing signal strenght of the interrogation signal as received by the tag: in that case, the reader 20 may also measure the signal intensity of the response signal for a more detailed measuring of the supply level in the transition region.

In the case of a dispenser for a liquid substance, such as soap, there basically are two systems for filling the dispenser. In one system, the container is an

exchangeable container, and refilling the dispenser is done by taking out the empty container and placing a new one. The container is typically placed in a housing part of the dispenser. In such case, the RFID tags of the present invention may be mounted on the actual replaceable container but may also be mounted on the dispenser housing, preferably internally. In another system, the container is an integral part of the dispenser, and the container is filled by pouring liquid substance into the container from a large supply vessel. In that case, there still may be an actual container within a housing, but it is also possible that the housing itself acts as container.

It is further noted that a replaceable container may be implemented as a rigid shape, for instance in the shape of a bottle, but may also be implemented as a collapsable bag. During use, the contents within the bag are reduced and the bag collapses. In such case, the bag itself can also act as signal interfering means.

A key aspect of the invention is the use of an RFID tag as a presence detector. Traditionally, the system of passive RFID tags has been deveiopped for and is being used for detecting the presence of the RFID sensor in the detection field or a reader, which in turn can be used to detect the presence of an object on which the tag is fixed. According to the inventive concept of the present invention, the tag is stationary but its reception is or is not disturbed by another object, not attached to the tag, so that the response or not by the tag is indicative for the presence or absence of such other object close to the tag.

In the above, the principles of the invention have been described for the situation of monitoring a level of substance: the "other object" close to the stationary tag here is the substance itself, or an object displaced by the substance. However, the principles of the present invention can be applied in other fields as well. One example to be mentioned here is the use of a passive RFID tag placed in the seat of a chair, wherein the RF reception of the tag is unobstructed and the associated reader will receive the tag's ID code if the chair is empty, and wherein the RF reception of the tag is obstructed and the associated reader will not receive the tag's ID code if the chair is occupied by a human. In that case, the tag associated with the chair can detect the occupancy by any human. Based on this detection, a system can decide to take an action. For instance, when the chair is the chair of a car, a seatbelt warning system may decide to issue a warning signal for the seatbelt or not, or, in case of a crash, an airbag system may decide to active the airbag or not, and a rescue system may call rescue services while informing them of the number of occupants.

In an other example, an automatic building management system is used to automatically switch of the light if a room is empty. Such systems typically are based on the use of movement detectors. However, when an office worker is working behind is desk, it may be that he is hardly moving, and it is annoying when the lights are regularly switched off. In current systems, the users have "learned" themselves to regularly move sufficiently such as to be noticed by the system. According to the invention, it is possible to use an office chair equipped with a passive RFID tag, and an automatic building management system equipped with an RF reader, so that the presence of the office worker is noticed even when he is sitting still.

In another example, an automatic filling system may detect the level of flushing water in a toilet reservoir.

In another example, a warning system may detect the level of water in a cellar or in the hull of a ship to warn against flooding.

In another example, passive RFID tags can be applied on the outside surface of a vehicle (truck, car, trailer, caravan, etc) as a simple and easy-to-install distance warning sensor, to avoid damages when parking because of not noticing an obstacle, without the need to install expensive ultrasonic sensors plus wiring.

It should be clear to a person skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that several variations and modifications are possible within the protective scope of the invention as defined in the appending claims.

In the above, the present invention has been explained with reference to block diagrams, which illustrate functional blocks of the device according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, microcontroller, digital signal processor, etc.