Method for determining a change in filling level and system for same

Abstract

The invention relates to a method for determining a change in the filling level in a container. In order to achieve a particularly accurate change in the filling level even in the case of only small changes in the filling level, the invention proposes that the container is excited and an oscillation behaviour of the container, in particular an echo characteristic and / or a natural frequency, is detected, after which the oscillation behaviour is compared with an oscillation behaviour of the container recorded at an earlier point in time and a change in the filling level is inferred if a deviation of the oscillation behaviour exceeds a predefined threshold value. The invention further relates to a system for determining a change in the filling level in a container, comprising a device for mechanically exciting the container, in particular a signal generator, and a sensor for detecting an oscillation characteristic, in particular an echo characteristic and / or a natural frequency of the container, in particular an ultrasonic sensor.

Description

[0001] Method for determining a change in fill level and system for this purpose

[0002] The invention relates to a method for determining a change in fill level in a container.

[0003] The invention further relates to a system for determining a change in fill level in a container, comprising a device for mechanically exciting the container, in particular a signal transmitter, and a sensor for detecting a vibration characteristic, in particular an echo characteristic and / or a natural frequency of the container, in particular an ultrasonic sensor.

[0004] Various methods and systems for determining fill level changes are known from the prior art. Conventional systems generally rely on using a distance sensor, which can be, for example, an ultrasonic or infrared sensor, to determine the distance from the top edge of the container to the surface of a substance inside the container, in order to determine the fill level based on this distance.

[0005] However, such systems and methods have proven unsuitable for determining whether a container is completely empty or contains at least a thin-walled object. This is crucial for level-based emptying of certain containers, such as mailboxes, especially since it must be ensured that a mailbox is emptied, for example, on the next working day, even if only a single letter has been deposited in it. Given the inherent tolerances, current state-of-the-art methods cannot reliably and efficiently determine whether a mailbox contains only a single letter, for example, lying flat at the bottom, or whether the mailbox is empty. Therefore, according to current state-of-the-art methods, mailboxes are still emptied at predetermined intervals, such as daily, regardless of the actual fill level.Due to the increasing prevalence of electronic communication, postal workers frequently visit empty mailboxes, generating costs for these wasted trips without any mail being delivered. This is where the invention comes in. The object of the invention is to provide a method of the type mentioned above, with which a change in fill level can be determined with high accuracy, even when only a very flat object is placed in a container.

[0006] Furthermore, a system for carrying out such a procedure should be specified.

[0007] The first problem is solved according to the invention by a method of the type mentioned at the outset, in which the container is excited and a vibration behavior of the container, in particular an echo characteristic and / or a natural frequency, is recorded, after which the vibration behavior is compared with a vibration behavior of the container recorded at an earlier time and, in the case of a deviation of the vibration behavior exceeding a predefined threshold value, a change in the fill level is inferred.

[0008] Within the scope of the invention, it was recognized that the vibration behavior, in particular the echo characteristics and the natural frequency of the container, changes significantly even when only a single object is placed in the container, for example, a letter in a mailbox. By recording the vibration characteristics and comparing them with a vibration characteristic recorded at an earlier time, it is thus possible to determine reliably and simply whether the fill level has changed compared to the previous measurement.

[0009] The vibration characteristics can be recorded, for example, by mechanically exciting the container or a volume within the container to vibrate, for instance, using a signal transmitter such as a loudspeaker emitting an ultrasonic signal, or a striking device such as a hammer, or similar, after which vibrations of the container itself or an acoustic signal inside the container are measured. A comparison of the current vibration behavior with previous vibration behavior can be made by directly comparing the recorded vibration over a specific time period, for example, 15 seconds after excitation. Alternatively or additionally, a frequency analysis of the measured signal can be performed to identify dominant frequencies in the vibration response, which may be characteristic of a particular fill level.For example, the natural frequency of the container can change significantly by inserting a single letter, so that a change in the fill level can be reliably detected by recording the natural frequency.

[0010] Determining a change in fill level can be achieved solely by measuring changes in vibration behavior. However, the quality of the result can be improved by also recording additional parameters that may influence the vibration behavior.

[0011] For example, to achieve a particularly accurate result, it may be preferable to measure the temperature along with the vibration behavior and, when comparing the measured vibration behavior with the vibration behavior measured at an earlier time, also compare the temperature with the temperature measured at that earlier time. Any deviations in the measured vibration behavior from the vibration behavior recorded at the earlier time should be taken into account, as these changes are attributable to temperature variations. It has been shown that the vibration behavior of a container changes with temperature, and therefore, considering the temperature change to which the container has been exposed since the reference measurement (i.e., the measurement of the vibration behavior at the earlier time) is suitable for improving the accuracy of determining changes in fill level.This can be taken into account, for example, by empirically or computationally determining how a temperature change affects the vibration behavior, such as the echo characteristics or the natural frequency of the container. Subsequently, based on the actual temperature change since the reference measurement, a change in the vibration behavior attributable to the temperature change is calculated. This calculated change is then subtracted from the actual change in vibration behavior to determine the change in vibration behavior caused by a possible change in fill level. If this remaining change exceeds a threshold, which can also be determined empirically or computationally, a change in fill level can be inferred.It is understood that, in addition to temperature, other parameters can also be recorded that affect the vibration behavior of the container, in order to avoid concluding that a change in fill level is solely due to a change in vibration behavior, which is due to factors independent of the fill level such as temperature or the like.

[0012] Furthermore, it is preferably provided that humidity is also measured along with the vibration behavior, and that when comparing the measured vibration behavior with the vibration behavior measured at an earlier time, the humidity is also compared with the humidity measured at that earlier time. Any deviations of the measured vibration behavior from the vibration behavior recorded at an earlier time are taken into account, as these changes are attributable to a change in humidity. A change in humidity particularly affects the speed of sound, which is why a change in humidity can also affect the echo characteristics inside a container. By taking into account a change in humidity since the reference measurement, the accuracy of determining the fill level change can thus be improved.This can be taken into account, for example, by empirically or computationally determining how a change in humidity affects the vibration behavior, such as the echo characteristics or the natural frequency of the container. Subsequently, based on the actual change in humidity since the reference measurement, a temperature-related change in the vibration behavior is calculated. This calculated change is then subtracted from the actual change in vibration behavior to determine the change in vibration behavior caused by a possible change in fill level. If this remaining change exceeds a threshold, which can also be determined empirically or computationally, a change in fill level can be inferred.

[0013] Preferably, the vibration behavior is measured along with the barometric pressure, and when comparing the measured vibration behavior with the vibration behavior measured at an earlier time, the barometric pressure is also compared with the barometric pressure measured at an earlier time. Any deviations in the measured vibration behavior from the vibration behavior measured at an earlier time are taken into account, as changes in the vibration behavior are attributable to changes in the barometric pressure. For example, a change in barometric pressure also results in a change in the speed of sound, which affects the echo characteristics.

[0014] In order to exclude errors in determining a change in fill level which are due to a change in barometric pressure, it is therefore preferably provided that changes in barometric pressure are taken into account when analyzing the change in vibration behavior.

[0015] To determine the effects of temperature changes, changes in humidity, and changes in barometric pressure on vibration behavior, it may be possible to determine the vibration behavior at different temperatures, humidity levels, and pressures, either computationally and / or empirically, and to correlate the measured or calculated data with changes in temperature, humidity, and pressure in order to determine the influences that the individual parameters have on the vibration behavior.To determine the change in vibration behavior that is due to parameters independent of the fill level, in particular temperature, pressure and humidity, the correlation found can then be used to infer the change in vibration behavior caused by the change in these parameters based on the measured changes in temperature, pressure and humidity since the reference measurement, so that the part of the change in vibration behavior that is not due to changes in these parameters can be determined, and thus a change in fill level can be inferred.

[0016] As an alternative to comparing the vibration behavior or echo with that of a known empty container, it is also possible to compare a current vibration behavior, particularly an echo, with a previously recorded vibration behavior, particularly a recent echo, to detect changes in fill level. Especially when echoes are recorded at regular intervals, this allows for highly accurate detection of fill level changes. It is advantageous to measure the vibration behavior of an empty container and then compare a subsequent measurement with that of the empty container. This measurement of the vibration behavior of an empty container can be performed, for example, upon delivery or after emptying, thus establishing a reference value at which the container is definitively empty.

[0017] It can also be provided that an empty container state, which triggers a reference measurement of the vibration behavior when empty, is determined acoustically, optically, mechanically, in particular by detecting movements and / or accelerations, by comparison with an emptying plan and / or the route of an emptying vehicle. For example, a sensor such as a microphone, an accelerometer, and / or an optical sensor can be provided inside the container with which changes in position, acoustic, and / or optical signals, which are typically associated with emptying, can be detected in order to determine an empty container state.

[0018] It goes without saying that such a sensor can also be used to trigger a vibration measurement to detect a change in fill level, for example when the sensor detects a change in position, an acoustic and / or an optical signal which is significant for an object being thrown into the container.

[0019] Furthermore, an empty container state and / or a change in fill level can be detected by mechanically, optically, and / or acoustically monitoring a container opening, particularly a lid opening. This state or change in state can then be used to record the vibration behavior. For example, movements such as changes in position or angle at the container opening or a closure through which material can be added and / or emptied can be mechanically detected using motion and / or acceleration sensors, optically, and / or acoustically. This allows conclusions to be drawn about times when a change in fill level is more likely to occur, so that vibration behavior can subsequently be recorded based on this increased probability of a change in fill level.

[0020] It is advantageous to analyze the vibration behavior at fixed time intervals and then infer a change in the fill level if the vibration behavior changes by more than a predefined threshold within a predefined time interval. For example, a very slow change in the vibration behavior could be caused by a temperature change, a pressure change, a change in humidity, or aging effects of the container. The rate at which the vibration behavior changes can be used to infer a change that, for example, might not indicate a change in the fill level due to a low rate alone, or, conversely, a particularly high rate that cannot be plausibly explained by other factors strongly suggests a change in the fill level.

[0021] It can also be provided that a temperature is measured continuously or at regular intervals, and that a vibration behavior measurement is triggered if the measured temperature changes by more than a predefined amount between two measurements. Measuring the temperature in or on the container requires less energy than measuring vibration behavior; therefore, measuring vibration behavior triggered by a temperature change results in a particularly energy-efficient method. It is understood that a combination of the triggers—time elapsed and temperature change—is possible, and thus the vibration behavior can be measured both at fixed intervals and upon detecting temperature changes.It goes without saying that other triggers can also be used if necessary, such as changes in pressure, humidity, and the like.

[0022] A change in vibration behavior can be, for example, a change in one or more natural frequencies of the container by more than a predefined threshold frequency, for example, more than 0.5 Hz, a change in echo loudness after a predefined time by more than a predefined amount, which can be measured, for example, in mV or dB, or an area under an envelope that is superimposed on an acoustic signal, in particular an echo, within a predefined period of time, for example, an envelope over a measured acoustic signal in a period that begins with the excitation and ends 15 seconds after the excitation.

[0023] To achieve a high-quality determination of fill level changes, the temporal progression of changes in vibration behavior can be analyzed. For example, a change in vibration behavior occurring within a few seconds or minutes can indicate a change in fill level, such as from a letter being placed in a mailbox. Conversely, a change in vibration behavior lasting several days or weeks, and occurring continuously, may indicate a change in vibration behavior caused solely by changes in temperature, pressure, humidity, or other factors unrelated to the fill level. Therefore, considering the rate of change in vibration behavior can improve the accuracy of the fill level change determination.When assessing changes in fill level based on the rate of change in vibration behavior, currently measured data regarding vibration behavior are preferably compared with the most recently measured data.

[0024] In a method for emptying a mailbox, wherein emptying the mailbox is triggered by a change in the fill level, it is advantageous if the change in the fill level is determined in a method according to the invention.

[0025] Changes in the mailbox level can be transmitted to a central data processing unit, which then triggers emptying whenever the mailbox level changes within a predefined time interval, for example, within less than 24 hours or less than a week. Since mailboxes that are already empty and have not experienced any changes in level since the last emptying are not emptied, the emptying of multiple mailboxes within a postal system can be made significantly more efficient, as unnecessary trips are avoided.Although a change in fill level can be determined solely by detecting a change in vibration behavior, an optical detection of the interior of a container and / or a distance measurement to detect an object in the container can be carried out in addition to achieve particularly precise measurement accuracy.

[0026] The further problem is solved according to the invention by a system of the type mentioned at the outset, which is set up for recording measured vibration characteristics and for comparing a currently measured vibration characteristic with a stored vibration characteristic.

[0027] Preferably, the system is designed to carry out a method according to the invention.

[0028] The system can, for example, include a signal transmitter such as an ultrasonic transmitter for emitting an ultrasonic signal or a hammer for striking the container, a sensor for detecting the vibration behavior or a vibration response that results after the excitation is sent by means of the signal transmitter, such as an ultrasonic sensor or a microphone, and a data storage device, in which, for example, an acoustic signal following excitation by means of the ultrasonic sensor or a quantity derived from it such as a frequency spectrum can be stored in order to be able to compare corresponding signals measured at a later time with earlier signals.

[0029] A change in fill level can then be easily inferred by the fact that a current signal or vibration characteristic deviates from a previous vibration characteristic by more than a predefined threshold, which can be specified in Hz, dB, or mV, or a derived quantity. The system typically includes a data processing unit such as a microcontroller, which can be used to assess changes in vibration behavior and thus detect changes in fill level.It is advantageous to have a data modem and a central data processing unit, whereby data relating to changes in fill level and / or data relating to detected vibration behavior, in particular measured data relating to acoustic signals or measured ultrasonic signals, can be transmitted to the central data processing unit via the data modem, especially via a mobile network. If a change in fill level is detected, the emptying of the container can then be triggered centrally, for example, by automatically initiating a vehicle trip to empty the container.

[0030] To enable the system to operate autonomously, i.e., without an external power supply, a local energy storage system, particularly a battery, is preferred. The system can also be designed to be very energy-efficient, using an ultrasonic transmitter, a corresponding sensor, a data storage device, and a modem, so that a single battery can provide power for several years.

[0031] Of course, it is also possible to provide a battery which can be charged, for example, by moving part of the container or by means of photovoltaic cells.

[0032] It is particularly advantageous if the system has a compact design, especially if it can be installed inside a mailbox, particularly on the inside of a lid. The system can be glued to the mailbox or connected to it by a force-fit or form-fit connection.

[0033] In order to take into account changes in vibration behavior caused by temperature changes when determining level changes, a temperature sensor is preferably provided.

[0034] To account for changes in vibration characteristics caused by fluctuations in humidity, it is advantageous to include a humidity sensor. Furthermore, it has proven beneficial to include a pressure sensor to measure air pressure. This allows for the consideration of vibration characteristic changes resulting from air pressure variations, preventing the detection of incorrect level readings when only temperature, humidity, or pressure has changed.

[0035] Additionally, the system, which is preferably arranged on the inside of a container lid, can include a distance sensor, which can be, for example, an infrared or ultrasonic sensor, to additionally detect an object located in the container by means of distance measurement. Such a measurement can also be used to detect when a container is emptied and subsequently perform a reference measurement.

[0036] Further features, advantages, and effects of the invention will become apparent from the exemplary embodiment described below. The drawings referred to therein show:

[0037] Fig. 1 shows a flowchart of a method according to the invention;

[0038] Fig. 2 Diagrams of a measured vibration behavior in a container.

[0039] Fig. 1 shows a flowchart of a method according to the invention for determining a change in fill level. According to this flowchart, after the system is started, in a first step 1, in which it is known that the container is empty, the container is excited or a signal is introduced into the container, in the exemplary embodiment using an ultrasonic transmitter. Subsequently, a vibration response of the container is detected internally by means of an ultrasonic sensor. An acoustic signal in the ultrasonic range is recorded for, for example, ten or fifteen seconds after the excitation, i.e., an echo, which is thus characteristic of an empty container and can serve as a reference measurement.

[0040] Furthermore, in this process step, the temperature inside the container, the humidity, and the relative humidity are also measured and recorded. In a further, second process step 2, a new measurement is triggered. This can occur due to the elapsed time since process step 1, for example, one minute or one hour, or due to a signal from a sensor indicating a change in fill level, in particular a signal from an accelerometer or an acoustic or optical signal. For example, the system can also be configured to detect tampering with the container, preferably a mailbox, using an accelerometer, acoustically, and / or optically, in order to record times when a change in fill level is highly likely to occur.

[0041] Process step 2 triggers a new measurement, which is carried out in process step 3. In process step 3, the container is again excited using the ultrasonic transmitter, and a vibration response is determined. For this purpose, the vibration behavior is again analyzed, with another measurement being taken using an ultrasonic sensor inside the container. If necessary, a derived quantity can be determined from this measurement, for example, a frequency spectrum using frequency analysis.

[0042] In this process step 3, temperature, pressure and humidity are again measured along with the vibration behavior.

[0043] In a fourth process step, the vibration behavior measured in process step 3 is compared with the vibration behavior measured in process step 1, taking into account changes in vibration behavior resulting from changes in temperature, pressure, or humidity. For this purpose, the effects of temperature, pressure, and humidity changes on the vibration behavior can be determined empirically or computationally and, in particular, stored in a system memory via correlation coefficients. This allows conclusions to be drawn about the resulting changes in vibration behavior based on measured changes in temperature, pressure, and humidity. Changes in vibration behavior that are not due to changes in pressure, temperature, or humidity are therefore considered to be caused by a change in the fill level.The result of process step 4 is therefore the signal difference between the signals measured in process steps 3 and 1, possibly corrected for changes due to temperature, pressure and humidity changes.

[0044] In the next step, it is investigated whether the change in vibration behavior between steps 3 and 1, possibly after subtracting the changes caused by changes in pressure, temperature, and humidity, exceeds a predefined threshold. This threshold is sufficiently high so that tolerances in the ultrasonic transmitter and receiver alone do not trigger a threshold violation. In a further step 5, it is then checked whether the result of the subtraction performed in step 4 is above the threshold.

[0045] If the change in vibration behavior exceeds this threshold, a change in the fill level is inferred, which can trigger emptying in process step 6, for example, by means of a vehicle that empties the container. The emptying can be used to perform a new reference measurement, which can be compared with subsequent measurements to determine a change in fill level, i.e., a filling, so that the process is repeated starting with process step 1.

[0046] If the change in vibration behavior is below the threshold value, the process continues with step 2, i.e., after a predefined time interval or upon the occurrence of a specific event, such as an acoustic event in the mailbox, a new measurement is carried out in step 3.

[0047] Although the exemplary embodiment describes the comparison of a current measurement with a reference measurement with an empty container, alternatively or additionally, the result of a current measurement of an echo or other measurement of the vibration behavior can also be compared with one or more other, previous measurements. For example, particularly when measurements are carried out at regular time intervals, a comparison with a previous measurement can always be performed to detect a change in fill level based on a comparatively large change in the vibration behavior within a specific time interval. Fig. 2 shows two diagrams, with the upper diagram showing envelopes over the time courses of measured values ​​from an ultrasonic sensor. The solid line represents a vibration response, i.e., a recorded acoustic signal or...An echo characteristic is shown following excitation of an empty container, which serves as a reference measurement. The dashed line shows an envelope of a vibration response or acoustic signal within the container after excitation when a single letter is present. A further dotted line shows another vibration response after the insertion of a letter. The solid line thus represents the result of the reference measurement, while the dashed and dotted lines represent comparative measurements.

[0048] The lower diagram of Fig. 2 shows differences between the echoes with letter and the echo without letter, i.e. the dashed and dotted envelopes minus the reference measurement shown as a solid line, each over time, for example 10 seconds after excitation.

[0049] As can be clearly seen from the signal difference shown in the lower diagram, the echo characteristics change significantly between the empty container and the container containing letters. Therefore, a change in the echo characteristics can be used to infer a change in the fill level. For automated detection of a fill level change, an area under the difference between the comparative and reference measurements shown in the lower diagram can be compared with a threshold value. If the threshold value is exceeded, a change in the fill level can be inferred. To increase the accuracy of the fill level change detection, additional parameters such as pressure, temperature, and humidity can be recorded. Furthermore, it is possible to combine a distance measurement with the method according to the invention to achieve even higher measurement quality.

[0050] With a method and system according to the invention, a change in the fill level of a mailbox or other container can thus be determined in a particularly simple and at the same time process-reliable way, thereby avoiding trips to empty containers, while at the same time ensuring that letters deposited are quickly removed from the mailbox.

Claims

Patent claims 1. Method for determining a change in fill level in a container, characterized in that the container is excited and a vibration behavior of the container, in particular an echo characteristic and / or a natural frequency, is recorded, after which the vibration behavior is compared with a vibration behavior of the container recorded at an earlier time and, in the case of a deviation of the vibration behavior exceeding a predefined threshold value, a change in fill level is inferred.

2. Method according to claim 1, characterized in that a temperature is also measured along with the vibration behavior and, when comparing the measured vibration behavior with the vibration behavior measured at an earlier time, the temperature is also compared with the temperature measured at an earlier time, wherein, in the case of deviations of the measured vibration behavior from the vibration behavior recorded at an earlier time, changes in the vibration behavior which are due to a temperature change are taken into account.

3. Method according to claim 1 or 2, characterized in that humidity is also measured along with the vibration behavior and, when comparing the measured vibration behavior with the vibration behavior measured at an earlier time, the humidity is also compared with the humidity measured at an earlier time, wherein, in the case of deviations of the measured vibration behavior from the vibration behavior recorded at an earlier time, changes in the vibration behavior which are due to a change in humidity are taken into account.

4. Method according to one of claims 1 to 3, characterized in that a barometric pressure is also measured along with the vibration behavior and, when comparing the measured vibration behavior with the vibration behavior measured at an earlier time, the barometric pressure is also compared with the barometric pressure measured at an earlier time, wherein, in case of deviations of the measured vibration behavior from that measured at an earlier time, Vibration behavior: Changes in vibration behavior are taken into account, which are due to changes in barometric pressure.

5. Method according to one of claims 1 to 4, characterized in that the vibration behavior is measured with the container empty and subsequent measurements of the vibration behavior are compared with the vibration behavior of the empty container.

6. Method according to one of claims 1 to 5, characterized in that a current vibration behavior, in particular an echo, is compared with a last recorded vibration behavior, in particular a last echo.

7. Method according to claim 6, characterized in that an empty container state, which triggers the performance of a reference measurement of the vibration behavior with an empty container, is determined acoustically, optically, mechanically, in particular by detecting movements and / or accelerations, by comparison with an emptying plan and / or a route of an emptying vehicle.

8. Method according to one of claims 1 to 7, characterized in that the vibration behavior is analyzed at fixed time intervals and a change in the fill level is then inferred if the vibration behavior changes by more than a predefined threshold value within a predefined time interval.

9. Method according to one of claims 1 to 8, characterized in that a temperature is measured continuously or at regular time intervals and a recording of the vibration behavior is triggered if the measured temperature has changed by more than a predefined amount between two measurements.

10. Method for emptying a mailbox, wherein emptying of the mailbox is triggered by a change in the fill level, characterized in that that the change in fill level is determined in a method according to one of claims 1 to 9.

11. Method according to one of claims 1 to 10, characterized in that, in addition, an optical detection of the interior of a container and / or a distance measurement is carried out to detect an object in the container.

12. System for determining a change in fill level in a container, comprising a device for mechanically exciting the container, in particular a signal transmitter, and a sensor for detecting a vibration characteristic, in particular an echo characteristic and / or a natural frequency of the container, in particular an ultrasonic sensor, characterized in that the system is configured for recording measured vibration characteristics and for comparing a currently measured vibration characteristic with a stored vibration characteristic, in particular for carrying out a method according to one of claims 1 to 9.

13. System according to claim 12, characterized in that a data modem and a central data processing unit are provided, wherein data relating to the change in fill level can be transmitted to the central data processing unit by means of the data modem.

14. System according to claim 12 or 13, characterized in that a local energy storage device, in particular a battery, is provided.

15. System according to one of claims 12 to 14, characterized in that the system can be installed in a letterbox, in particular on the inside of a lid.

16. System according to one of claims 12 to 15, characterized in that a temperature sensor is provided.

17. System according to one of claims 12 to 16, characterized in that a humidity sensor is provided for determining air humidity.

18. System according to one of claims 12 to 17, characterized in that a pressure sensor is provided for determining air pressure.

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