阅读说明：本技术 电子防盗系统和方法 (Electronic anti-theft system and method ) 是由 维尔纳·法尔肯伯格 瑟伦·厄斯特高·桑达尔 于 2020-04-08 设计创作，主要内容包括：一种电子防盗系统,包括：第一多轴磁力计和第二多轴磁力计(101),被配置为输出表示第一磁场矢量的运动的第一矢量信号(vs0)；以及信号处理器(501),耦接为接收第一矢量信号(vs0)和第二矢量信号(vs1)并且被配置为：根据第二矢量信号(vs1)与第一补偿信号之间的差值的优化来确定第一多维变换(T1)；其中,根据第一多维变换(T1)从第一矢量信号(vs0)的变换生成第一补偿信号；并且从第二矢量信号(vs1)和第一补偿信号生成补偿的第二矢量信号。此外,确定响应于补偿的第二矢量信号的检测器信号(D)满足预定标准；并且至少响应于确定检测器信号满足预定标准,发出或放弃发出警告关于可能的盗窃相关事件的第一警报。(An electronic theft prevention system comprising: a first and a second multi-axis magnetometer (101) configured to output a first vector signal (vs0) representing a motion of a first magnetic field vector; and a signal processor (501) coupled to receive the first vector signal (vs0) and the second vector signal (vs1) and configured to: determining a first multi-dimensional transformation (T1) from an optimization of the difference between the second vector signal (vs1) and the first compensation signal; wherein a first compensation signal is generated from a transformation of the first vector signal (vs0) according to a first multi-dimensional transformation (T1); and generating a compensated second vector signal from the second vector signal (vs1) and the first compensation signal. Furthermore, determining that a detector signal (D) responsive to the compensated second vector signal satisfies a predetermined criterion; and in response to at least determining that the detector signal meets the predetermined criteria, issuing or forgoing issuing a first alarm warning about a possible theft-related event.)

1. An electronic theft prevention system comprising:

a first multi-axis magnetometer (101) arranged in a first station at a first position and configured to output a first vector signal (vs0) representing motion of a first magnetic field vector;

a second multi-axis magnetometer (102, 104) arranged in a second station at a second position and configured to output a second vector signal (vs1, vs3) representing motion of a second magnetic field vector; and

a signal processor (501) coupled to receive the first vector signal (vs0) and the second vector signal (vs1) and configured to:

determining a first value of a parameter of a first multi-dimensional transformation (C1) according to an optimization of a difference between the second vector signal (vs1) and a first compensation signal (cs 1); wherein the first compensation signal is generated from a transformation of the first vector signal (vs0) according to the first multi-dimensional transformation (C1);

generating a compensated second vector signal (cvs1) from the second vector signal (vs1) and the first compensation signal (cs 1);

determining that a detector signal (D) responsive to the compensated second vector signal satisfies a predetermined criterion; and is

Issuing or forgoing issuing a first alarm warning about a possible theft-related event at least in response to determining that the detector signal satisfies the predetermined criterion.

2. An electronic theft prevention system according to claim 1, wherein the first value of the parameter of the first multidimensional transformation (C1) is determined on a round-robin basis according to a first timing (T1, T2, T3).

3. The electronic theft prevention system as claimed in claim 2,

wherein the difference between the second vector signal (vs1) and the first compensation signal (cs1) is determined over a parallel time period or a fraction of the parallel time period of the first vector signal (vs0) and the second vector signal (vs 1); and is

Wherein the compensated second vector signal (cvs1) is generated from the second vector signal (vs2) at a time after the parallel time period and in accordance with the first value re-determined on the loop basis.

4. Electronic theft prevention system according to any of the preceding claims, comprising:

a third multi-axis magnetometer (103, 105) arranged in the third station and configured to output a third vector (vs2) signal representing motion of a third magnetic field vector;

wherein the signal processor (501) is further configured to:

according to said third vector signal (A)₃) Optimization of the difference with the second compensation signal (cs2) to determine a second value of a parameter of the second multi-dimensional transform (T2); wherein the second compensation signal (cs2) is generated from a transformation of the first vector signal (vs0) according to the second multi-dimensional transformation (C2);

generating a compensated third vector signal (cvs2) from the third vector signal (vs2) and the second compensation signal (cs 2);

wherein the detector signal (D) is responsive to the compensated third vector signal (cvs 2).

5. Electronic theft prevention system according to any of the preceding claims, comprising:

a fourth multi-axis magnetometer (104, 106) arranged in the fourth station and configured to output a fourth vector (vs3, vs5) signal representing motion of a fourth magnetic field vector;

wherein the signal processor is further configured to:

determining a third value of a parameter of a third multi-dimensional transformation (C3) according to an optimization of the difference between the fourth vector signal (vs3) and a third compensation signal; wherein the second compensation signal is generated from a transformation of the first vector signal (vs1) according to the third multi-dimensional transformation (C3);

generating a compensated third vector signal from the third vector signal and the second compensation signal;

wherein the detector signal (D) is responsive to the compensated third vector signal.

6. The electronic theft prevention system according to any of the preceding claims wherein the signal processor is further configured to:

band-pass filtering one or more or all of the first, second, third and fourth vector signals by respective band-pass filters; wherein the respective band pass filters have a lower cut-off frequency below 1.0Hz and an upper cut-off frequency above 4Hz and below 50 Hz.

7. Electronic theft protection system according to one of the preceding claims, wherein one or more or all of the first (C1), second (C2) and third (C3) multidimensional transformations are estimated according to a regularization applied during iterative estimation of transformed parameters, the regularization penalizing relatively large ones of the transformed parameters compared to relatively small ones.

8. The electronic theft prevention system as claimed in any one of the preceding claims wherein:

-acquiring said first vector signal (vs0) during a first time period (TS1) and a second time period (TS2), and acquiring said second vector signal (vs1) during said first time period (TS1) and said second time period (TS 2);

estimating a first parameter (C1) at a first time (T1) from the first vector signal (vs0) and the second vector signal (vs1) at the first time period (TS 1);

estimating a first parameter (C1') at a second time (T2) from the first vector signal and the second vector signal at the second time period;

generating the compensated second vector signal (cvs1) at a time subsequent to the second time (T2) according to a first criterion, according to a first parameter (C1) estimated at the first time (T1);

according to a second criterion, the compensated second vector signal is generated at a time after the second time (T2) according to the first parameter (C1') estimated at the second time (T2).

9. Electronic theft protection system according to claim 8, wherein the first criterion is fulfilled when the compensated second vector signal (cvs1) generated from the second vector signal (vs1) at the first time period (TS2) according to the first parameter (C1') estimated at the second time (T2) has a lower strength than the compensated second vector signal (csv1) generated from the second vector signal (vc1) at the first time period according to the first parameter (C1) estimated at the first time (T1).

10. The electronic theft prevention system as claimed in any one of the preceding claims wherein:

at a first time: estimating a first parameter (C1) based on the first vector signal (vs0) for the first time period (TS1), the second vector signal (vs1) for the first time period (TS1) and the first compensation signal for the first time period (TS 1); wherein the first compensation signal for the first time period (TS1) is generated from the first parameter (C1) estimated at the first time (T1) and the first vector signal (vs0) for the first time period (TS 1);

at a second time: estimating a first parameter (C1') based on the first vector signal (vs0) for the second time period (TS2), the second vector signal (vs1) for the second time period (T2) and the first compensation signal for the second time period; and a first parameter (C1') estimated from the second time and the second time periodGenerates the first compensation signal (C)₂·A₀)；

Generating a first compensated second vector signal (cvs1) from the second vector signal (vs1) for the second time period (TS2) and the first compensated signal from the first parameter (C1) estimated at the first time and the first vector signal for the second time period;

generating a second compensated second vector signal (cvs1 ') from the second vector signal (vs1) for the second time period and the first compensated signal from the second time estimated first parameter (C1') and the first vector signal for the second time period;

the signal processor is further configured to:

estimating said first compensated second vector signal (cvs1) and said second compensated second vector signal, and

determining that the first compensated second vector-signal (cvs1) is better than the second compensated second vector-signal (cvs 1'), and generating the compensated second vector-signal (cvs1) based on the first parameters estimated at the first time, and forgoing generating the compensated second vector-signal based on the first parameters estimated at the second time.

11. Electronic theft protection system according to any one of the preceding claims, wherein the signal processor (501) is further configured to:

detecting the corresponding movement of the first and second magnetic field vectors is performed by:

-estimating a first rotation of the first magnetic field vector and a second rotation of the second magnetic field vector;

-generating an indication signal comprising an indication of a counter rotation or a co-rotation;

-determining whether to enable the first alarm at least in response to the indication signal.

12. The electronic theft prevention system according to any of the preceding claims wherein the signal processor is further configured to:

-detecting a corresponding movement of the first and second magnetic field vectors;

-detecting the onset and the persistence of a fluctuation of at least the first or the second magnetic field vector after detecting a corresponding motion of the magnetic field vector; wherein the duration of the fluctuation is accurately determined according to a first timing scale;

-determining whether to issue or forgo issuing a first alarm warning about a possible theft-related event at least in response to determining the onset and duration of the fluctuation of at least the first or second magnetic field vector.

13. The electronic theft prevention system according to any one of claims 11 to 12 wherein detecting corresponding movement of the first and second magnetic field vectors comprises:

-determining whether the movement of the first and second magnetic field vectors corresponds to a substantially horizontal movement of a magnet between the first and second stations.

14. The electronic theft prevention system according to any one of claims 11 to 13 wherein detecting the continuation of the fluctuation comprises:

-determining whether the movement of one or both of the first and second magnetic field vectors corresponds to an oscillating movement of a magnet in the vicinity of one or both of the first and second stations.

15. A method of detecting a theft-related event,

at a system comprising: a first multi-axis magnetometer arranged in the first station and configured to output a first vector signal representing motion of the first magnetic field vector; a second multi-axis magnetometer arranged in the second station and configured to output a second vector signal representing motion of a second magnetic field vector; and a signal processor coupled to receive the first vector signal and the second vector signal:

estimate the firstA multi-dimensional transformation (C)_n) A first multi-dimensional transformation representing a difference between the first magnetic field vector and the second magnetic field vector and estimated over a period of time according to an optimization of the difference between the first vector signal and the second vector signal;

in response to a transformation from (C) to (D) said first multi-dimensional_n) A first compensation signal generated by the defined transformation of the second vector signal, compensating the second vector signal;

determining that a detector signal (D) responsive to the compensated second vector signal satisfies a predetermined criterion; and is

Issuing or forgoing issuing a first alarm warning about a possible theft-related event at least in response to determining that the detector signal satisfies the predetermined criterion.

Technical Field

Theft, also known as shoplifting, is a problem for many retailers, especially those who sell consumer products such as clothing, clothing that is relatively easy to conceal under coats, handbags, and the like, especially where a fitting room is available.

Electronic Article Surveillance (EAS) is known in the art to trigger an alarm and possibly prevent the removal of merchandise from a store or shopping area in an unauthorized manner.

According to conventional EAS systems, a salesperson attaches an electromagnetic tag to merchandise, such as to more expensive merchandise. The antenna is placed near the entrance/exit of a store or shopping area and is coupled to a circuit that detects passing tags affixed to items. Typically, the tag is removed when the item is paid at a checkout counter. Thus, when a tag is detected passing between the antennas, it is typically a theft-related event.

Despite the widespread installation of such systems, theft remains a major problem for retailers at almost every store, for example, those selling clothes or even those selling food.

It is recognized that a person intending to perform a theft enters a store or shopping area with a magnet configured to unlock a lock holding the tag affixed to merchandise. Then, in the store, they remove the label from the article and leave the label. They then take the merchandise out of the store without triggering any alarm via conventional EAS alarm systems.

Such a magnet configured to unlock a lock that attaches the above-described tag to an article is called a separator, a separation magnet, or an unlocking magnet. However, such a separate magnet is difficult to detect because it is easily confused with other magnetic objects present and even moves within and around the shopping area. A magnet may be used for the lock of the bag and, for example, the metal part in the shoe or bag may be embodied as a magnet.

One problem is that automatic detection is prone to generate false alarms, or that a magnet is not detected when it should be detected. In this regard, it should be noted that sales personnel and customers who may be misdirected to theft are very disliked of false alarms.

Background

EP 2997557B 1 relates to automatically detecting when a detaching magnet enters a shop or shopping area and describes an electronic anti-theft system that sounds an alarm when a strong magnet used in the detacher enters the shopping area. This electronic anti-theft system includes: first and second multi-axis magnetometers arranged in the first and second stations and configured to output first and second vector signals representing motion of first and second magnetic field vectors, respectively; and a signal processor coupled to receive the first vector signal and the second vector signal and configured to: estimating a first rotation of the first magnetic field vector and a second rotation of the second magnetic field vector; generating an indication signal comprising an indication of a counter rotation or a co-rotation; and determining whether to issue or inhibit an alarm signal warning about a possible theft-related event at least in response to the indication signal. The system issues a warning if the unlocking magnet for the anti-shoplifting tag passes between stations, for example, when a station is located on each side of the entrance to the shopping area.

However, it is desirable to further improve the reliability associated with detecting theft-related events.

Disclosure of Invention

It has been observed that in some places, and sometimes with existing systems (e.g., systems that detect separate magnets), reliably detecting theft-related events is a problem. Thus, existing systems generate false alarms or fail to issue an alarm when an alarm should be issued. It is also observed that conventional temporal filtering may be sufficient in some cases, but not in all cases. Therefore, the inventors devised:

an electronic theft prevention system comprising:

a first multi-axis magnetometer (101) arranged in a first station at a first position and configured to output a first vector signal (vs0) representing motion of a first magnetic field vector;

a second multi-axis magnetometer (102, 104) arranged in a second station at a second position and configured to output a second vector signal (vs1, vs3) representing motion of a second magnetic field vector; and

a signal processor (501) coupled to receive the first vector signal (vs0) and the second vector signal (vs1) and configured to:

determining a first value of a parameter of the first multi-dimensional transformation (C1) according to an optimization of a difference between the second vector signal (vs1) and the first compensation signal (cs 1); wherein a first compensation signal (cs1) is generated from a transformation of the first vector signal (vs0) according to a first multi-dimensional transformation (C1);

generating a compensated second vector signal (cvs1) from the second vector signal (vs1) and the first compensation signal (cs 1);

determining that a detector signal (D) responsive to the compensated second vector signal satisfies a predetermined criterion; and is

Issuing or forgoing issuing a first alarm warning about a possible theft-related event in response to at least determining that the detector signal satisfies the predetermined criterion.

Thus, theft-related events can be detected more reliably and the risk of generating false alarms or failing to issue alarms at least at times when an alarm should be issued is reduced.

In particular, but not limited thereto, theft-related events can be reliably detected despite the presence of interfering magnetic fields emitted by high-power electromagnetic devices. High power electromagnetic devices may be associated with overhead contact lines, for example, associated with railways, subway lines, trams, and the like.

Interference from e.g. high power electromagnetic devices can be suppressed in the compensated second vector signal using a first compensation signal, which is obtained via the first transformation and the information in the first vector signal. The first transformation may accommodate, for example, one or both of a rotation transformation and a scaling transformation. The first transformation may represent a difference between the first magnetic field vector and the second magnetic field vector.

The first multi-axis magnetometer may be placed at a distance from the second multi-axis magnetometer within a range of a few meters (e.g., 1-20 meters). According to the claimed system, spatial information related to the disturbing magnetic field is included in the first transformation, since the first magnetometer senses the magnetic field at the position of the first station, which is different from the position of the second station. The first vector signal is acquired at a different location than the second vector signal. The second multi-axis magnetometer may be placed in close proximity to an area where it is desired to detect a theft-related event, such as an access area, fitting room area, or aisle. The first multi-axis magnetometer may be placed in a location closer to the source of the magnetic field (such as an overhead contact line of a train, subway or bus line) and/or in a location where passage by customers is not desired (at least not often).

Thus, the signal processor enables more effective filtering of interference from electromagnetic devices than conventional time domain filtering. It has been found that despite the presence of electromagnetic devices that emit strong electromagnetic fields, the claimed system is able to substantially suppress the effects of interfering magnetic fields to more reliably detect theft-related events.

The second multi-axis magnetometer may sense theft-related events alone or in combination with one or more additional multi-axis magnetometers (e.g., in combination with the first multi-axis magnetometer).

The compensated second vector signal is compensated using information from the first multi-axis magnetometer. In particular, a first multi-dimensional transformation is applied such that the first vector signal is available to compensate the second vector signal.

In some embodiments, first values of parameters of the first multi-dimensional transform (C1) are determined on a round-robin basis according to a first timing (T1, T2, T3).

Thus, despite the presence of a time-varying disturbing magnetic field emitted by the high-power electromagnetic device, a theft-related event can be reliably detected. For example, it is observed that time-varying disturbing magnetic fields emitted by overhead contact lines, e.g. associated with railways, subway lines, trams, etc., attract offset levels of substantially DC current. Such time-varying disturbing magnetic fields alternate regularly or irregularly and may occur at a frequency related to theft-related events occurring in the vicinity of the second station.

In some aspects, in response to the first value of the parameter being re-determined on a recurring basis according to the first timing, a compensated second vector signal is generated from the second vector signal according to the first value being re-determined on a recurring basis. Therefore, the most recent first value is used for compensation.

The first values of the parameters of the first multi-dimensional transform may be determined at regular intervals (e.g., every 30 seconds, every 60 seconds, every 3 minutes) or at other regular or irregular intervals.

In some embodiments, the difference between the second vector signal (vs1) and the first compensation signal (cs1) is determined over parallel time periods or portions of parallel time periods of the first vector signal (vs0) and the second vector signal (vs 1); and generating a compensated second vector signal (cvs1) from the second vector signal (vs2) at a time after the parallel time period and in accordance with the first value re-determined on a loop basis.

Thus, the most recent first value of the parameter based on the first transformation is compensated and the compensated second vector signal adapts faster to the changing disturbing magnetic field.

The concurrent time period (i.e., the current time period) may or may not overlap or be continuous or discontinuous with the previous concurrent time period.

In some embodiments, an electronic theft prevention system includes:

a third multi-axis magnetometer (103, 105) arranged in the third station and configured to output a third vector (vs2) signal representing motion of a third magnetic field vector;

wherein the signal processor (501) is further configured to:

determining a second value of a parameter of the second multi-dimensional transform (T2) according to an optimization of a difference between the third vector signal (a3) and the second compensation signal (cs 2); wherein a second compensation signal (cs2) is generated from a transformation of the first vector signal (vs0) according to a second multi-dimensional transformation (C2);

generating a compensated third vector signal (cvs2) from the third vector signal (vs2) and the second compensation signal (cs 2);

wherein the detector signal (D) is responsive to the compensated third vector signal (cvs 2).

The second and third multi-axis magnetometers may be located on each side of a passageway, for example, a passageway to a shopping area or a passageway to a fitting room.

Thus, the second and third stations may be located on opposite sides of the aisle. The first station may be located at a first distance from any of the second and third stations, wherein the first distance is greater than (e.g., at least twice) the distance between the second and third stations.

The second and third values of the respective transformations may be different, although the distance between the second station and the first station is relatively small. For example, the first magnetometer may have a different orientation than one or both of the second magnetometer and the third magnetometer. It may also happen that one or more magnetometers are changed orientation, intentionally or unintentionally.

One or both of the compensated second vector signal and the compensated third vector signal may be processed to issue or forgo issuance of an alarm warning about a possible theft-related event. This is described in more detail in EP 2997557B2 related to channels and application PCT/EP2018/077148 related to fitting rooms.

In some embodiments, an electronic theft prevention system includes:

a fourth multi-axis magnetometer (104, 106) arranged in the fourth station and configured to output a fourth vector (vs3, vs5) signal representing motion of a fourth magnetic field vector;

wherein the signal processor is further configured to:

determining a third value of a parameter of the third multi-dimensional transformation (C3) based on an optimization of the difference between the fourth vector signal (vs3) and the third compensation signal; wherein a second compensation signal is generated from a transformation of the first vector signal (vs1) according to a third multi-dimensional transformation (C3);

generating a compensated third vector signal from the third vector signal and the second compensation signal;

wherein the detector signal (D) is responsive to the compensated third vector signal.

One or more or all of the compensated second, third and fourth vector signals may be processed to issue or forgo issuance of an alarm warning about a possible theft-related event. This is also described in more detail in EP 2997557B2 related to channels and application PCT/EP2018/077148 related to fitting rooms.

In some embodiments, the signal processor is further configured to: band-pass filtering one or more or all of the first, second, third and fourth vector signals by respective band-pass filters; wherein the respective band pass filters have a lower cut-off frequency below 1.0Hz and an upper cut-off frequency above 4Hz and below 50 Hz.

The band pass filter can effectively remove offsets corresponding to the earth's magnetic field and AC noise, e.g., from electrical appliances, motors, etc., occurring at frequencies above 4Hz to above 50 Hz.

In some aspects, band pass filtering is applied to provide the vector signal as a band pass filtered vector signal. Thus, the vector signal may be a band-pass filtered vector signal. This improves the effectiveness of the compensation, since the transformation can be estimated more accurately when the offset corresponding to the earth's magnetic field and AC noise, for example, from an electrical appliance, is removed in advance.

The band pass filter may be implemented by a low pass filter and a high pass filter or by a first low pass filter and a second low pass filter coupled via a summing unit to output a difference signal as known in the art.

In some embodiments, one or more or all of the first multi-dimensional transform (C1), the second multi-dimensional transform (C2), and the third multi-dimensional transform (C3) are estimated according to a regularization applied during iterative estimation of parameters of the transforms, the regularization penalizing relatively larger ones of the parameters of the transforms as compared to relatively smaller ones of the parameters of the transforms.

Regularization prevents or suppresses overfitting. This is advantageous because in general one direction of the magnetic field vector in three-dimensional space is much stronger than the other directions. This helps to suppress overfitting in the other directions. The regularization may be L1 regularization or L2 regularization or another type of regularization. The regularization constrains (regularizes) the coefficient estimates to zero. In other words, the technique discourages learning more complex or flexible models to avoid the risk of overfitting.

In some embodiments, the first vector signal (vs0) is acquired during a first time period (TS1) and a second time period (TS2), and the second vector signal (vs1) is acquired during the first time period (TS1) and the second time period (TS 2); estimating a first parameter (C1) at a first time (T1) from a first vector signal (vs0) and a second vector signal (vs1) at a first time period (TS 1); estimating a first parameter (C1') at a second time (T2) from the first vector signal and the second vector signal at a second time period; generating a compensated second vector signal (cvs1) at a time after the second time (T2) in dependence on the first parameter (C1) estimated at the first time (T1) in accordance with a first criterion; and generating, according to a second criterion, a compensated second vector signal at a time after the second time (T2) according to the first parameter (C1') estimated at the second time (T2).

In this way, the system can adapt to improved parameters that can be estimated on an ongoing basis. The first and second time periods may be consecutive time periods, e.g., having a duration of 30 seconds to 120 seconds or less or more. The first and second time periods may overlap in time or be spaced apart to occur at regular or irregular times.

In some embodiments, the first criterion is fulfilled when the compensated second vector signal (cvs1) generated from the second vector signal (vs1) at the first time period (TS2) according to the first parameter (C1') estimated at the second time (T2) has a lower intensity than the compensated second vector signal (csv1) generated from the second vector signal (vc1) at the first time period according to the first parameter (C1) estimated at the first time (T1).

Thus, the strength provides a metric and a mutual threshold for estimating whether to update or maintain the parameters over time. Thus, the system may accommodate time varying magnetic fields and/or repositioning and/or rotation of the station and/or magnetometer relative to each other. This greatly reduces the frequency of service attendance by the system and serves to further reduce the frequency of false alarms or failure to raise alarms at the time they should be raised.

In some embodiments of the present invention, the,

at a first time: estimating a first parameter (C1) based on the first vector signal (vs0) for the first time segment (TS1), the second vector signal (vs1) for the first time segment (TS1) and the first compensation signal for the first time segment (TS 1); wherein a first compensation signal for a first time period (TS1) is generated from a first parameter (C1) estimated at a first time (T1) and a first vector signal (vs0) for the first time period (TS 1);

at a second time: estimating a first parameter (C1') based on the first vector signal (vs0) for the second time period (TS2), the second vector signal (vs1) for the second time period (T2) and the first compensation signal for the second time period; and generating a first compensation signal from the second time estimated first parameter (C1') and the first vector signal for the second time period; generating a first compensated second vector signal (cvs1) from the second vector signal (vs1) for the second time segment (TS2), and generating a first compensated signal from the first parameter (C1) estimated at the first time and the first vector signal for the second time segment; generating a second compensated second vector signal (cvs1 ') from the second vector signal (vs1) for the second time period and a first compensated signal from the first parameter (C1') estimated for the second time and the first vector signal for the second time period; the signal processor is further configured to:

estimating a first compensated second vector signal (cvs1) and a second compensated second vector signal, and

determining that the first compensated second vector signal (cvs1) is better than the second compensated second vector signal (cvs 1'), and generating a compensated second vector signal (cvs1) based on the first parameters estimated at the first time, and forgoing generating the compensated second vector signal based on the first parameters estimated at the second time.

In some embodiments, the signal processor (501) is further configured to: the detection of the corresponding movement of the first magnetic field vector and the second magnetic field vector is performed by:

-estimating a first rotation of the first magnetic field vector and a second rotation of the second magnetic field vector;

-generating an indication signal comprising an indication of a counter rotation or a co-rotation;

-determining whether the first alarm is enabled at least in response to the indication signal.

This is also described in more detail in EP 2997557B2 in relation to channels.

In some embodiments, the signal processor is further configured to:

-detecting a corresponding movement of the first magnetic field vector and the second magnetic field vector;

-detecting the start and duration of a fluctuation of at least the first or second magnetic field vector after detecting the corresponding movement of the magnetic field vector; wherein the duration of the fluctuation is determined in accordance with a first timing criterion;

-determining whether to issue or forgo issuing a first alarm warning about a possible theft-related event at least in response to determining the onset and duration of the fluctuation of at least the first magnetic field vector or the second magnetic field vector.

In some embodiments, detecting the corresponding motion of the first magnetic field vector and the second magnetic field vector comprises:

-determining whether the movement of the first and second magnetic field vectors corresponds to a substantially horizontal movement of the magnet between the first and second stations.

In some embodiments, detecting the duration of the fluctuation comprises:

-determining whether the movement of one or both of the first and second magnetic field vectors corresponds to an oscillating movement of the magnet in the vicinity of one or both of the first and second stations.

This is also described in more detail in the application PCT/EP2018/077148 related to fitting rooms.

There is also provided a method of detecting a theft-related event, comprising, at a system: a first multi-axis magnetometer arranged in the first station and configured to output a first vector signal representing motion of the first magnetic field vector; a second multi-axis magnetometer arranged in the second station and configured to output a second vector signal representing motion of a second magnetic field vector; and a signal processor coupled to receive the first vector signal and the second vector signal, comprising:

estimate the first multipleDimension transformation (C)_n) A first multi-dimensional transformation representing a difference between the first magnetic field vector and the second magnetic field vector and estimated over a period of time based on an optimization of the difference between the first vector signal and the second vector signal;

in response to a transformation from a first multi-dimensional (C)_n) A first compensation signal generated by transformation of the defined second vector signal, compensating the second vector signal;

determining that a detector signal (D) responsive to the compensated second vector signal satisfies a predetermined criterion; and is

Issuing or forgoing issuing a first alarm warning about a possible theft-related event in response to at least determining that the detector signal satisfies the predetermined criterion.

Drawings

The following is described in more detail with reference to the accompanying drawings, in which:

fig. 1 shows magnetometers of an anti-theft system, for example installed in the entrance area of a shopping area and a fitting room area;

fig. 2 shows magnetometers of an anti-theft system, for example installed in a fitting room area, comprising a first magnetometer and a second magnetometer;

fig. 3 shows magnetometers of an anti-theft system, for example installed in an entrance area, comprising a first magnetometer, a second magnetometer and a third magnetometer;

fig. 4 shows magnetometers of an anti-theft system, for example installed in a fitting room area, comprising a first magnetometer and a second magnetometer;

fig. 5 shows a first block diagram of a signal processor of the anti-theft system;

FIG. 6 shows a second block diagram of a signal processor of the anti-theft system; and

fig. 7 shows a timing diagram for estimating and using the transformed estimated parameters.

Detailed Description

The electronic anti-theft system is described below with respect to various embodiments, including at least a first multi-axis magnetometer 101 and a second multi-axis magnetometer 102, 104. Typically, the first multi-axis magnetometer 101 is arranged in a first station at a first position and is configured to output a first vector signal vs0 representing the motion of a first magnetic field vector. A second multi-axis magnetometer, e.g. represented by 102 and 104, is arranged in a second station at a second position and is configured to output a second vector signal vs1, vs3 representing the motion of a second magnetic field vector. The magnetic field vector refers to a representation of the physical magnetic field sensed by the respective magnetometer. In general, the magnetometers herein are shown in a Cartesian coordinate system having x, y and z axes. The magnetometers may be inclined relative to each other, although not shown here in this manner. The magnetometer package may include markings or symbols printed on its surface to indicate the orientation of its axis.

A signal processor (described further below) is coupled to receive the first vector signal vs0 and the second vector signal vs 1. The signal processor, e.g., one or more processors configured to run a program, to generate at least one compensated vector signal and determine that a detector signal responsive to the compensated vector signal satisfies a predetermined criterion; and in response to at least determining that the detector signal meets the predetermined criteria, issuing or forgoing issuing a first alarm warning about a possible theft-related event. In some embodiments, the signal processor is coupled to receive additional one or more vector signals, e.g., vs2 and vs 3. In some embodiments, a plurality of signal processors are used, each coupled to receive two or more vector signals. The vector signals may be transmitted from the respective stations to the signal processor via a wireless or wired connection. Furthermore, the one or more signal processors may be coupled to the alarm transmitter, for example to a mobile alarm transmitter, by a wireless or wired connection.

Herein, a vector signal is a digital vector signal, comprising three sample values (e.g., designated x)_i、y_iAnd z_i) One sample value for each of three mutually orthogonal dimensions (e.g., x, y, and z). The magnetometer may be of a digital type outputting a digital value or of an analog type outputting an analog signal, which is then converted to a digital vector signal by an analog-to-digital converter. The digital signals may be communicated according to the I2C standard, the bluetooth standard, or according to another protocol.

Before turning to the details of the signal processor, the configuration of a system of multi-axis magnetometers arranged in respective stations at respective positions and configured to output respective vector signals is described.

Fig. 1 shows an example of a system of magnetometers, for example an anti-theft system installed in the entrance area of a shopping area and a fitting room area. The system 100 of magnetometers comprises:

i) a first multi-axis magnetometer 101 outputting a first vector signal vs 0;

ii) a first set 115 of magnetometers 102 and 103 outputting respective vector signals vs1 and vs 2; and

iii) a second group 108 of magnetometers 104, 105, 106 and 107.

The first set 115 of magnetometers 102 and 103 may be arranged on opposite sides of a pathway, indicated by arrow 117, which pathway may be an entrance to a shopping area, such that a person entering the shopping area passes between magnetometers 102 and 103. The channel between the magnetometers may also be referred to as a "gate". Persons who do not need to pass through the door access shopping area may pass along arrow 116. As described in more detail in EP 2997557B2, it may be determined that a person carrying a separate magnet (or a magnetically similar object) passes through the door along arrow 117 or that a person carrying a separate magnet passes along arrow 116. One or more "doors" may be installed in this manner. One or more magnetometers may be used for two adjacent gates to reduce the number of magnetometers required.

The second group 108 of magnetometers 104, 105, 106 and 107 may be arranged in a fitting room area, for example a shopping area. In some embodiments, each fitting room requires at least one magnetometer to distinguish which fitting room issues an alarm in the event a theft-related event is detected. Fitting rooms are indicated as 109, 110 and 111 and are accessible through corresponding channels indicated by arrows 112, 113 and 114. Here, magnetometers 104, 105, 106 and 107 are arranged to form a door at the entrance of each fitting room. As described in more detail in EP 2997557B2, it can thus be determined that a person is entering a fitting room with a separate magnet. As described in more detail in patent application PCT/EP2018/077148, it can be determined whether a predetermined and possible theft-related movement of the separation magnet occurs in a given fitting room.

Importantly, the system of magnetometers comprises a first multi-axis magnetometer 101. The first multi-axis magnetometer 101 is positioned at a distance, e.g., within a few meters (e.g., 1-20 meters), from the second multi-axis magnetometer. Here, the second multi-axis magnetometer may be any one of the magnetometers 102, 103, 104, 105, 106 and 107. The magnetometers of the first group 108 may be positioned at a mutual distance of, for example, approximately 0.5 meters to 2 meters or more or less, depending on the size of the fitting room. The magnetometers of the second group 115 may be positioned at a mutual distance of e.g. about 1 meter to 4 meters or more or less, depending on the position of the other alarm stations with respect to the entrance positioning. The first multi-axis magnetometer 101 can be placed closer to the magnetic field source (such as an overhead contact line of a train, subway, or bus line) and/or in a location where passage by customers is not desired (at least not often).

The system of magnetometers may include fewer or more groups of magnetometers to obtain a desired detection area or gates.

Fig. 2 shows an example of a system of magnetometers (including a first magnetometer and a second magnetometer) of an anti-theft system installed in a fitting room area, for example. The system 200 of magnetometers comprises a first magnetometer 101 and a second magnetometer 104. The system 200 may be used, for example, in conjunction with a fitting room 109. Thus, a simpler system is provided. The system may be implemented as described in patent application PCT/EP 2018/077148.

As will be described in more detail below, for the system 200 of magnetometers, the signal processor is configured to calculate values of parameters of the first multi-dimensional transformation C1 and to generate a compensated second vector signal from the second vector signal vs1, the first vector signal vs0 and the first transformation C1. The transformation C1 is illustrated by the dashed line denoted C1.

Fig. 3 shows an example of a system of magnetometers (including a first magnetometer, a second magnetometer and a third magnetometer), such as an anti-theft system installed in an entrance area. The system of magnetometers 300 comprises a first magnetometer 101, a second magnetometer 102 and a third magnetometer 103. The system 300 may be used, for example, in conjunction with one or both of the entrance area and the fitting room.

For the system 300 of magnetometers, the signal processor is configured to calculate values of parameters of the first multi-dimensional transformation C1 and values of parameters of the second multi-dimensional transformation C2. Further, the signal processor is configured to generate:

i) a compensated second vector signal from the second vector signal vs1, the first vector signal vs0 and the first transform C1; and

ii) the compensated third vector signal from the third vector signal vs2, the first vector signal vs0 and the second transform C2.

The transformations C1 and C2 are illustrated by the dashed line denoted C1 and the dashed line denoted C2.

Fig. 4 shows an example of a system of magnetometers (including a first magnetometer and a second magnetometer) of an anti-theft system installed in a fitting room area, for example. The system 400 of magnetometers comprises a first magnetometer 102 and a second magnetometer 103. The system 400 may be used, for example, in conjunction with one or both of the entrance area and the fitting room.

For the system 400 of the magnetometer, the signal processor is configured to calculate values of parameters of the first multi-dimensional transformation C1, and to generate a compensated second vector signal from the second vector signal vs2, the first vector signal vs0 and the first transformation C1. The transformation C1 is illustrated by the dashed line denoted C1. Thus, the first magnetometer 102 may itself be used as a "door" or fitting room magnetometer.

Fig. 5 shows a first block diagram of an example of a signal processor of the anti-theft system. The first block diagram may be implemented by a part of hardware and/or software of the signal processor. The signal processor 501 is coupled to receive a first vector signal vs0, a second vector signal vs1 and a third vector signal vs 3.

The band pass filters 502 filter one or more or all of the first, second and third vector signals through the respective band pass filters. The corresponding band pass filter has a lower cut-off frequency below about 1.0Hz and an upper cut-off frequency above about 4Hz and below about 50Hz, for example at-3 dB. The band pass filter may effectively remove offsets corresponding to the earth's magnetic field and AC noise, for example, from appliances, motors, etc. having switched, rotating or reciprocating electromagnetic circuits. For simplicity, the vector signals input to and output from the band pass filter are denoted by the same reference numerals. In some embodiments, the band pass filter may be omitted.

The time periods of the first, second and third vector signals vs0, vs1, vs2 are stored in buffers denoted as [ vs0], [ vs1] and [ vs2 ]. The buffer may be rewritten with the most recent time period at regular intervals (e.g., every 30 seconds).

The signal processor has a first branch configured to calculate a first transformation C1 and to calculate a compensated second vector signal cvs 1. Furthermore, the signal processor has a second branch configured to calculate a second transformation C2 and to calculate a compensated third vector signal cvs 2.

The first branch is based on an estimator 'Est' 503 configured to determine a first value of a parameter of the first multi-dimensional transformation C1 according to an optimization of the difference between the second vector signal vs1 and the first compensation signal cs 1; wherein the first compensation signal is generated from a transformation of the first vector signal vs0 according to a first multi-dimensional transformation C1. More specifically, the estimator is configured to optimize the following expression according to an optimization algorithm, e.g., a L-BFGS (Low memory Broyden-Fletcher-Goldfarb-Shanno) algorithm.

Wherein, vs_nIs a vector signal (N x 3 matrix; where N is the number of samples in the buffer), e.g. from the second vector signal vs 1; vs. v_n0(N × 3 matrix) is the first vector signal vs 0; k is a constant; c_nIs a3 x 3 transform matrix; i and j are summation variables; and |. | represents a 1-norm.

The transformation transforms the 3D representation of the first vector into a 3D representation of the second vector. The transformation may have parameters representing one or both of rotation and scaling. The parameters of the transformation may be stored in one or more variables, such as in an array as is known in the art. The signal processor may discard the memory operations associated with all elements of the 3 x 3 matrix, for example, if the transform includes 5 non-zero parameters.

Here, the optimization may be a minimization of e. When summing the values stored in the buffer, the above expression is iteratively optimized to minimize e_n(summing the values in the buffer is not shown in the above expression). The last term of the above expression is the so-called L1 regularization. Regularization penalizes parameter values C of a relatively large transformation compared to parameter values of a relatively small transformation_n. Regularization prevents or suppresses overfitting. Instead of L1 regularization, other types of regularization may be applied.

May be after a predetermined number of iterations or after a predetermined period of time or when the threshold e is reached_nA stopping criterion known in the art is applied to obtain the transformed values.

The transformation (e.g., C1) may be computed in other ways (e.g., using other optimization algorithms selected from, for example, the steepest descent algorithm class).

In response to the value of the transformation C1 available after the above iterative computation, the signal processor may generate a compensated second vector signal cvs1 from the second vector signal vs1 and the first compensation signal cs1, the first compensation signal being generated from a transformation of the first vector signal vs0 according to the first multidimensional transformation C1 available after the iterative computation. The compensated second vector signal cvs1 may be generated by the summing unit 505 calculating the difference between the second vector signal vs1 and the first compensation signal cs 1. The difference may be calculated as a conventional difference or in another way.

The second leg is based on the estimator 'Est' 504 and operates as described above.

The compensated second vector signal cvs1 and the compensated third vector signal cvs2 generated from the first branch and the second branch, respectively, are input to the vector processor 'VP' 707. Vector processor 507 receives the vector signal, processes the vector signal and generates a detector signal (D). The vector processor 507 may operate as described in more detail in EP 2997557B2 or PCT/EP 2018/077148. Thus, the compensated vector signals described herein are input to the vector processor instead of receiving uncompensated vector signals as described in EP 2997557B2 and PCT/EP 2018/077148.

The detector signal D is input to an alarm unit which determines that the detector signal meets a predetermined criterion. The predetermined criterion may be that the alarm is enabled by the enable signal and the detector signal makes a predetermined transformation or reaches a predetermined threshold. In response to at least determining that the detector signal meets the predetermined criteria, the alarm unit 508 issues or forgoes issuing an alarm warning about a possible theft-related event.

The alert may be communicated via a wireless transmission device, such as radio circuit 508, to a mobile device carried by, for example, a store clerk.

In another example, the signal processor 501 is coupled to receive a first vector signal vs0, a second vector signal vs3, and a third vector signal vs 4. In other examples, the signal processor is coupled to receive the first vector signal vs0, the second vector signal vs3, the third vector signal vs4, the fourth vector signal vs5, and the fifth vector signal vs 6. The signal processor is configured to process the vector signal with the necessary modifications. In addition to the first vector signal, one or more or all of the vector signals may be processed to generate a compensated vector signal.

Fig. 6 shows a second block diagram of a signal processor of the anti-theft system. The second block diagram may be implemented by a part of hardware and/or software of the signal processor. The signal processor 601 may be part of the signal processor 501 or interconnected with the signal processor 501. The signal processor 601 is configured to estimate the values of the first transformation over the course of time.

The time periods of the first vector signal vs0 and the second vector signal vs1 are stored in buffers denoted as [ vs0] and [ vs1 ]. The buffer may be rewritten with the most recent time period at regular intervals (e.g., every 30 seconds or every 180 seconds) or at other intervals.

As described above, the values of the parameters of the first transformation C1 may be calculated by an iterative algorithm. First, C1 has been calculated during the time period TS1 and is available at the first time T1 (see fig. 7). Also as described above, the compensated second vector signal cvs1 may be generated via summing units 603 and 604. The compensated second vector signal cvs1 is input to estimator "Eval" 602. Second, at a later point in time T2, the values of the parameters of the first transformation are recalculated, as represented by C1 ', which C1' has been calculated during the time period TS2 and is available at a second time T2 (see fig. 7). A compensated second vector signal cvs1 'based on the transformation C1' may be generated. The compensated second vector signal cvs 1' is also input to estimator "Eval" 602. Thus, the estimator 602 receives the compensated second vector signal cvs1 and the compensated second vector signal cvs 1'.

The estimator 602 may estimate two versions of the compensated second vector signal to determine which first transformation C1 or C1' to use to calculate the compensated second vector signal for at least some future time periods.

The estimator 602 may estimate two versions of the compensated second vector signal, for example according to the expression calculated for cvs1 and cvs 1' as follows:

wherein Sig represents a measure of signal strength; |.. | represents a 1-norm; m (e.g., M600) represents the number of samples in a time period, x_i、y_iAnd z_iRepresenting three sample values at time or sample instance i, respectively, one sample value for each of three mutually orthogonal dimensions (e.g., x, y, and z).

The estimator 602 may determine that C1 'results in a lower signal strength by comparing the respective values of | Sig |, and thus determine to replace C1 with C1' for at least some future time periods. Alternatively, the estimator 602 may calculate a compensated vector signal by comparing the respective values of | Sig | to determine that C1 results in a lower signal strength, and thus determines that C1 remains for at least some future time period, rather than replacing C1 with C1'.

The above estimation may be performed on a round-robin basis according to predetermined timing (e.g., at times T1, T2, T3, etc.). To save memory, C1 may contain the transform of the vector signal currently used to compute the compensation, while C1' may represent the most recent candidate transform. Therefore, although C1 is calculated from the time period before the time periods stored in the buffers [ vs0] and [ vs1], C1 is compared with C1' calculated from the time periods stored in the buffers [ vs0] and [ vs1 ]. The buffers [ vs0] and [ vs1] contain parallel time segments of the first vector signal vs0 and the second vector signal vs 1.

Fig. 7 shows a timing diagram for estimating and using the transformed estimated parameters. The timing diagram is shown as a function of time t. The first and second vector signals vs0, vs1 are shown over time and in particular over time periods TS1, TS2 and TS3 elapsed at times T1, T2 and T3, respectively.

It is also shown that the calculation 'comp.' of the first value of the first parameter of the first transformation occurs from T1 to T1a, as indicated by the pointing block denoted C1, and is available at a first time T1a after T1. Subsequently, the recalculation of the first value of the first parameter of the first transformation occurs from T2 to T2a, as indicated by the pointing block denoted C1', and is available at a first time T2a after T2.

As described above, the signal processor may determine that C1 is better than C1', and continue to use C1. This is shown with respect to label "C _ a". Alternatively, as described above, the signal processor may determine that C1 'is better than C1, and use C1' instead of C1, as shown with respect to label "C _ B".

The signal processor may be configured to process a pair of vector signals, e.g., vs0 and vs1, or to process multiple vector signals simultaneously using the disclosure provided above. For example, the signal processor 501 may omit the second branch to include the first branch.

There is also provided an electronic theft prevention system, comprising:

a first multi-axis magnetometer (101) arranged in a first station at a first position and configured to output a first vector signal (vs0) representing motion of a first magnetic field vector;

a second multi-axis magnetometer (102, 104) arranged in a second station at a second position and configured to output a second vector signal (vs1, vs3) representing motion of a second magnetic field vector; and

a signal processor (501) coupled to receive the first vector signal (vs0) and the second vector signal (vs1) and configured to:

determining a first value of a parameter of the first multi-dimensional transformation (C1) according to an optimization of a difference between the second vector signal (vs1) and the first compensation signal (cs 1); wherein a first compensation signal is generated from a transformation of the first vector signal (vs0) according to a first multi-dimensional transformation (C1);

generating a compensated second vector signal (cvs1) from the second vector signal (vs1) and the first compensation signal (cs 1);

determining that a detector signal (D) responsive to the compensated second vector signal satisfies a predetermined criterion; and is

Issuing or forgoing issuing a first alarm warning about a possible theft-related event in response to at least determining that the detector signal satisfies the predetermined criterion.

The above electronic theft prevention system may be configured with a magnetometer of one-dimensional type, and the first transformation may be a one-dimensional transformation such as multiplication or summation. Such an electronic theft prevention system may be equipped with a first magnetometer and a second magnetometer arranged in substantially the same orientation. The electronic theft prevention system may be mounted with the first magnetometer and the second magnetometer arranged in an orientation different from the mutually orthogonal orientation. The magnetometers may be arranged at a mutual orientation of less than about 60 ° (e.g., less than about 45 °). In some embodiments, the second station comprises a plurality of one-dimensional magnetometers arranged along a substantially vertical axis (e.g., arranged in an elongated, vertical or upright body or stand mount for fixing on a wall). Embodiments of the above electronic anti-theft system comprising a one-dimensional magnetometer, wherein the multi-axis magnetometer may be replaced by a one-dimensional magnetometer and/or a one-dimensional transform, are defined in the dependent claims and summary of the invention.

In some embodiments, the multi-axis magnetometer is a two-dimensional magnetometer. The electronic theft prevention system may be mounted with the first magnetometer and the second magnetometer arranged in an orientation different from the mutually orthogonal orientation. The magnetometers may be arranged at a mutual orientation of less than about 60 ° (e.g., less than about 45 °). The two-dimensional magnetometers may each have substantially orthogonal axes.

From the above it is clear that theft related events can be detected more reliably and at least the risk of generating false alarms or failing to issue alarms when they should be issued is reduced.