WO2001008080A2

WO2001008080A2 - Method for identifying objects on a moving conveyor

Info

Publication number: WO2001008080A2
Application number: PCT/FR2000/002139
Authority: WO
Inventors: Lassina Sanogo; Pierre Bonnefoy
Original assignee: Tagsys
Priority date: 1999-07-28
Filing date: 2000-07-26
Publication date: 2001-02-01
Also published as: FR2797123A1; WO2001008080A3

Abstract

The invention concerns a system for automatically identifying objects being transported on a moving conveyor (20) comprising a detection member, each object being provided with an electronic label. The invention is characterised in that the detection member consists of a rotary field antenna (110) consisting of two loops (B1, B2) located in the same plane and coupled in phase quadrature over an overlapping zone, the antenna (10) being generally rectangular in shape and located in a plane parallel to the conveyor (20). In another embodiment, the antenna (10) can further be oriented such that its axis of symmetry (105) forms an angle (α) with the displacement axis (25) of the conveyor (20).

Description

SYSTEM FOR IDENTIFYING OBJECTS ON A CONVEYOR

MOVEMENT .

The present invention relates to a dynamic system for automatically identifying objects on a moving conveyor.

The present invention essentially applies to the identification of objects moving in one dimension on a conveyor. All the objects are each provided with an electronic label responding to the request of a detection member constituted by a radiofrequency transmission-reception system. Several problems relate to such identification. First of all, the conveyor generally comprises a metal portion which absorbs a large part of the electromagnetic field emitted by the detection member. On the other hand, the detection members such as the antennas for example, generally have field holes along their axes of symmetry when the electronic tag to be identified is not located in a plane parallel to the plane of the antenna. . '^'' 1 Now, in the application which interests us,> e ^ electronic labels are fixed randomly on objects arranged randomly on a conveyor which move in a rectilinear manner. It is thus possible that certain objects cross the field of the antenna close to an axis of symmetry, without being detected.

The invention seeks to provide a dynamic identification system which allows the detection of any object moving on a metal conveyor, and regardless of the orientation of the electronic label worn by the object to be identified.

There are several radio frequency identification systems (RFID: Radio Frequency Identification in English) comprising a detection device such as an antenna detecting electronic tags assigned respectively to different objects.

Depending on the applications, the detection members can be of different shapes and positioned in different ways. |

Figure 1 illustrates the application in which the invention is located, that is to say in the context of objects moving rectilinearly on a metal conveyor. The conveyor 20 has a movement axis 25 along which objects 51, 52, 53 each carrying an electronic label 10 evolve. The conveyor generally has a width greater than the objects 50, 51, 52 that it conveys. It is therefore necessary that the field emitted by the detection member covers the entire width of the conveyor in order to detect all the objects whatever the distance at which they are from the edges.

Thus, an identification system using “gate” antennas, that is to say two antennas placed opposite each side of the conveyor, has the disadvantage of having a very weak field in the center because the metallic environment of the conveyor absorbs a large part of the electromagnetic field emitted. For such an application, an antenna situated in a plane parallel to the plane of the conveyor, and not far from the latter is more suitable. Such an antenna can have different geometric shapes. Another problem which the invention seeks to solve consists in detecting an object on a moving conveyor whatever the orientation of the electronic label placed on said object. Thus, in the case of an object of simple and reproducible shape, having a flat surface parallel to the plane of the conveyor, such as a box for example, the electronic label 10 can systematically be fixed on the top of the box in order to be in a plane parallel to that of the detection device (object 52). In such a configuration, identification is ensured.

However, there are applications in which the objects to be identified do not have such a simple shape, or for which precautions in positioning the label 10 have not been taken. On such objects (51 and 53), the electronic label can be fixed along a plane perpendicular to the conveyor and can be randomly oriented relative to the plane of the front of the detection antenna. The edge of the antenna is called its edge perpendicular to the axis of the conveyor.

The geometry of the antenna is therefore important. Indeed, there are identification systems using circular antennas, but this geometry is particularly ill-suited to the detection of objects on a moving conveyor because each diameter of the antenna includes a field hole for orientation of the label perpendicular to the plane of the antenna.

These field holes are not annoying for applications in which the objects move in two or three dimensions because they will then necessarily cross an area of intensity field. sufficient to be detected. This is the case of Electronic Article Surveillance (SEA) used in all department stores for example.

However, in the case of an object moving in one dimension, as is the case of an object stationary on a moving conveyor, it is possible that the object crosses the field of the circular antenna according to a diameter and it will not be detected. A rectangular antenna 100, | covering the entire width of the conveyor, is therefore more suitable for the application of object identification on a moving conveyor 20.

A rectangular antenna has two axes of symmetry 105 and 106 which constitute field holes for an electronic label 10 perpendicular to the plane of the conveyor 20 as is the case of the objects 51 and 53 of FIG. 1.

In such a configuration, in particular if the electronic label of an object to be identified is perpendicular to the plane of the conveyor and perpendicular to the plane of the front of the antenna (see FIG. 9b, case of object 53 of FIG. 1) , and that it crosses the antenna field at its center, it cannot be detected.

In order to overcome these drawbacks and to allow reliable identification of objects on a moving metal conveyor whatever the orientation of their electronic label, the invention proposes to provide a dynamic identification system comprising a device for detecting a particular geometry.

The present invention more particularly relates to an automatic object identification system moving on a moving conveyor comprising a detection member, each object being provided with an electronic label.

According to a first embodiment, the identification system is characterized in that the detection member is constituted by a rotating field antenna composed of two loops located in the same plane and coupled in phase quadrature on an overlap zone , the antenna being of generally rectangular shape and situated in a plane parallel to the plane of the conveyor.

The rotating field, obtained by coupling on a zone of overlap of two loops in which currents respectively phase shifted by π / 2 circulate, makes it possible to stir the field over the entire detection volume of the antenna. Indeed, the phase quadrature introduces a phase rotation between the two branches of the overlap zone which causes an alternation of change of sign of the electromagnetic field.

According to a first variant, the rotating field is obtained by injection of two phase-shifted currents of π / 2 dan the two loops of the antenna.

According to another variant, the rotating field e. ^c t obtained by induction of a current in a passive loop from a current injected into an active loop, the induced current being phase-shifted by π / 2 with respect to the injected current.

According to one characteristic, the surface of the overlap area of the rotating field antenna is adjustable.

According to an alternative embodiment, the rotating field antenna is also oriented so that its axis of symmetry makes an angle with the axis of moving the conveyor.

According to a second embodiment, the identification system is characterized in that the detection member is constituted by an antenna of generally rectangular shape located in a plane parallel to the plane of the conveyor and oriented so that its axis of symmetry makes an angle with the axis of movement of the conveyor.

According to one characteristic, the angle between the axis of symmetry of the antenna and the axis of the conveyor is between 5 ° and 40 °.

According to another characteristic, the electronic labels are located in any plane relative to the plane of the conveyor. According to a first embodiment, the antenna is located above the plane of the conveyor.

According to a second embodiment, the antenna is located below the plane of the conveyor.

According to a feature of these modes of implementation, the antenna is located at a distance less than or equal to 40 cm from the plane of the conveyor.

According to a third mode of implementation, the artennε is integrated into the plane of the conveyor. r- Seloi _' a feature, the antenna cost ^, ι J ^* the width of the conveyor.

The invention exploits a new antenna geometry in the context of an application to moving conveyors in order to ensure the detection of any object moving on such a conveyor whatever the orientation of the electronic label of the object.

Other features and advantages of the invention will become apparent on reading the description which is given below and which is given by way of illustrative and nonlimiting example and with reference to the drawings in which: FIG. 1, already described, is a diagram of a conveyor carrying objects to be identified; - Figure 2 schematically illustrates a first embodiment of the invention; Figure 3 schematically illustrates a third embodiment of the invention; Figures 4a and 4b illustrate the principle of a rotating field; Figure 5 is a graph of the currents of a rotating field antenna; FIG. 6 schematically illustrates a second embodiment of the invention; - Figures 7a and 7b illustrate the field for a label parallel to the plane of the conveyor, respectively for the first and the second embodiment of the invention; Figures 8a and 8b illustrate the field for a label perpendicular to the plane of the conveyor and parallel to the front of the antenna, respectively for the first and the second embodiment of the invention;

- ^" Figures 9a and 9b illustrate the lice field a label perpendicular to the plane of the conveyor and perpendicular to the front ^" of the antenna, respectively for the 'first and the second embodiment of the invention.

FIG. 2 illustrates a first embodiment of the invention. The identification system according to the invention comprises a detection member constituted by an antenna 110. According to a first characteristic essential to the invention, the antenna 110 is of generally rectangular shape, that is to say that it has two axes of symmetry 105 and 106. It can have slightly rounded edges without losing its generally rectangular shape .

According to a second characteristic essential to the invention, the antenna 110 is placed in a plane parallel to the plane of the conveyor 20 in order to cover its entire width. _

According to a third characteristic essential to this embodiment of the invention, the detection member is constituted by a rotating field antenna 110 composed of two loops Bi and B ₂ located in the same plane and coupled on an overlap zone C , conductive strands 111 and 112 of each loop delimiting this area C. Currents Ii and I ₂ , in phase quadrature, flow respectively in each branch Bi and B ₂ . The phase quadrature between the currents Ii and I ₂ of the two strands 111 and 112 can be obtained in different ways.

According to a first method, the two loops Bi and B ₂ are respectively controlled by two current amplifiers which inject into each loop alternating currents Ii and I ₂ . These ^amplifiers' are previously set in phase quadrature with respect to each other.

According to a second method, the rotating field antenna 110 consists of an active loop Bi and a passive loop B ₂ .

The active loop Bi receives an alternating current Ii injected by a current amplifier. This current Ii induces a current I ₂ in the passive loop B ₂ by a phenomenon of induction in the overlap zone C of the antenna 110. According to known physical properties, the induced current I ₂ is phase-shifted by π / 2 relative to the injected current Ii. This quadrature phase coupling, which will be explained later, allows the electromagnetic field of the antenna 110 to be mixed so as to eliminate the field holes and to guarantee a minimum field intensity over the entire area covered. through the antenna. - -

This coupling allows the antenna 110 to generate a rotating field for detecting ^an electronic tag whatever its orientation, even when it is perpendicular to the plane of the conveyor and perpendicular to the front of the antenna (Figure 9a).

However, even if a minimum field strength is guaranteed, as is clearly illustrated in FIGS. 7a, 8a and 9a, this field is not uniform and certain zones have minimum fields. In particular for a label 10 located in the plane of the antenna 110, two minima appear along the axis of symmetry 105 (FIG. 7a). However, in a metallic environment, it is necessary to guarantee a relatively high field on all the possible trajectories of a label 10.

This is why, according to an alternative embodiment, illustrated in FIG. 3, the rotating field antenna 110 is also oriented so that its axis of symmetry 105 has an angle of offset α with the axis of movement. 25 of the conveyor. Thus, a label, which by application, moves in a linear direction 25, cannot cross the entire detection area of the antenna 110 with a minimum of field. FIGS. 4a and 4b illustrate the effects of the quadrature phase coupling of the two loops Bi and

B ₂ of the rotating field antenna 110. Such a rotating field can be likened to the field generated by a rotating magnet placed opposite a fixed magnet.

When the conductive strands 111 and 112 of the overlap zone C are in phase, the intensity of the electromagnetic field in this zone C is very strong, while when the same strands are in phase opposition, the intensity of the electromagnetic field _ in zone C becomes almost zero.

Advantageously, the width of the overlap zone C is adjustable in order to allow optimal adjustment of the stirring of the electromagnetic field over the entire detection volume of the antenna 110.

FIG. 5 reports on a graph the temporal behaviors of the two currents ι _x and ι ₂ .

When one realizes the sum of the values of the currents iχ and ι ₂ (dotted curve) one goes through an alternation of positive and negative values. These changes in sign of the currents flowing in the antenna 110 cause changes in the direction of the electromagnetic field.

The frequency of the currents ι _x and / or l ₂ injected α in the loops B _X and B ₂ , or only in the active loop Bi are for example 13 MHz. The alternation of change of direction of the electromagnetic field will then be close enough to stir the field over the entire volume covered by the antenna 110. FIG. 6 illustrates the second embodiment of the identification system according to the invention for which the detection member is constituted by a single loop antenna 100. Such an antenna 100 is of generally rectangular shape, and is placed in a plane parallel to the plane of the conveyor 20 in order to cover its entire width.

The field hole generated by the axis of symmetry 106 appears for an electronic label 10 perpendicular to the plane of the conveyor and parallel to the plane of the front of the antenna (FIG. 8b). However, this field hole is perpendicular to the axis of movement 25 of the object 51 to be identified. The latter will therefore necessarily be detected by crossing areas of higher intensity field.

On the other hand, the field hole generated by the axis of symmetry 105 appears for an electronic label 10 perpendicular to the plane of the conveyor and perpendicular to the front of the antenna (see FIG. 9b). It is therefore possible that the object 53 crosses the field of the antenna 100 close to this axis of symmetry 105 without being able to be identified.

According to a characteristic essential to this embodiment of the invention, a rotation is therefore carried out so as to place the antenna 100 in an orientation such that its axis of symmetry 105 has an offset angle α with the axis of movement 25 of the conveyor 20. Thus, an object to be identified 53, evolving along the axis of movement 25 of the conveyor 20, cannot cross the entire surface covered by the antenna 100 along its axis of symmetry 105. It will therefore necessarily be detected by crossing an area in which there is a minimum of field.

Figures 7a to 9b show electromagnetic field simulations of a rectangular antenna located in a plane parallel to the conveyor. These figures illustrate the different possible distributions of electromagnetic field according to the orientation of the label 10 for a single loop antenna 100 and for a rotating field antenna 110.

It is clearly seen in these figures the advantage provided by the rotation α of the antenna 100, 110 in order to prevent the holes or the field minima being in the axis of movement 25 of the objects on the conveyor 20.

The orientation of the antenna 100, 110 depends on the modes of implementation and the applications, depending on the width of the conveyor and the size of the ^" - objects conveyed, the offset angle α can vary between 5 ° and

40 °, and preferential between 10 ° and 20 °.

According to the modes of implementation, the antenna 100, 110 can be located above the conveyor 20, below or it can be integrated into the conveyor.

When the antenna 100, 110 is above the conveyor 20, it is located in a plane parallel to a variable distance depending on the applications. It must not be too far away in order to detect all the objects despite the high absorption of the metal conveyor, and it must not be too low so as not to hinder the movement of the conveyed objects.

When the antenna 100, 110 is below the conveyor 20, the latter must necessarily be modified to allow the antenna to detect ^" the objects without its field being completely absorbed by the metal of the conveyor. Thus, a portion of the conveyor can be cut and replaced by plastic for example, the antenna being fixed under this portion.

Whether it is above or below, the antenna 100, 110 is preferably located at a distance less than or equal to 40 cm from the plane of the conveyor. A particularly advantageous mode of implementation from an industrial point of view consists in integrating the antenna 100 into the conveyor 20. As previously, a portion of the conveyor is cut out and replaced by a plastic portion in which the antenna 100 is placed.

This variant allows the antenna 100 to be brought as close as possible to the electronic labels of the moving objects in order to optimize their identification. An experimental realization was carried out -with a rotating field antenna 110 located 20 cm above the plane of the conveyor 20 and offset by an angle α of 15 °.

Claims

1. Automatic identification system for objects moving on a moving conveyor (20) comprising a detection member, each object being provided with an electronic label (10), characterized in that the detection member consists by a rotating field antenna (110) composed of two loops (Bi, B ₂ ) located in the same plane and coupled in phase quadrature on an overlap zone (C), the antenna (110) being of generally rectangular shape and located in a plane parallel to the plane of the conveyor (20).

2. Identification system according to claim 1, characterized in that each loop (Bi, B ₂ ) receives respectively a current (Ii, I∑) injected, said currents (Ii, I) being phase shifted by π / 2 l ' one over the other.

3. Identification system according to claim 1, characterized in that the loops (Bi, B) of the antenna (110) consist of an active loop

(Bi) in which a current (Ii) is injected, and a passive loop (B ₂ ) in which a current (I ₂ ) is induced, phase-shifted by π / 2 relative to the current (Ii) of the active loop (B _x ).

4. Identification system according to claim 1, characterized in that the surface of the overlap zone (C) is adjustable.

5. Identification system according to one of Claims 1 to 4, characterized in that the antenna with rotating field (110) is further oriented so that its axis of symmetry (105) makes an angle (α) with the axis of movement (25) of the conveyor (20).

6. Automatic identification system for objects moving on a moving conveyor (20) comprising a detection member, each object being provided with an electronic label (10), characterized in that the detection member consists by an antenna (100) of generally rectangular shape located: in a plane parallel to the plane of the conveyor (20) and oriented so that its axis of symmetry (105) makes an angle (α) with the axis of movement ( 25) of the conveyor

(20).

7. Identification system according to one of claims 5 or 6, characterized in that the angle

(α) between the axis of symmetry (105) of the antenna (100, 110) and the axis of movement (25) of the conveyor (20) is between 5 ° and 40 °.

8. Identification system according to any one of the preceding claims, characterized in that the electronic labels (10) are located αans any plane relative to the plane of the conveyor (20).

9. Identification system according to any one of claims 1 to 8, characterized in that the antenna (100, 110) is located above the plane of the conveyor (20).

10. Identification system according to any one of claims 1 to 8, characterized in that the antenna (100, 110) is located below the plane of the conveyor (20).

11. Identification system according to one of claims 9 or 10, characterized in that the antenna (100, 110) is located at a distance less than or equal to 40 cm from the plane of the conveyor (20).

12. Identification system according to any one of claims 1 to 8, characterized in that the antenna (100) is integrated into the plane of the conveyor (20).

13. Identification system according to any one of the preceding claims, characterized in that the antenna (100, 110) covers the entire width of the conveyor (20).