Abstract:
In order to provide a method for locating moving objects that will allow high precision in position determination and thus largely eliminate sorting errors, and also to provide a device suitable for executing the method, it is envisaged that on at least one defined location within the reading range of an interrogator ( 16 ) arranged in a stationary position, an interference pulse, which influences a response signal transmitted by a transponder ( 20 ) carried by a moving object ( 12 ) in response to a signal transmitted by the interrogator ( 16 ), is exerted on the object ( 12 ), and a position of the object ( 12 ) is determined in dependence on a time when the influence of the response signal occurred.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method and a device for locating moving objects, having the characteristic features of the preamble of claim  1  or of claim  10 . The invention further relates to applications of the method or the device. 
     2. Description of Related Art 
     For locating moving objects, arrangement of so-called transponders on the objects is known, these transponders being able to communicate with an interrogator arranged in a stationary position on a path of movement of the object. Here, transponders, chip cards and labels are grouped under the term transponder (often also called “tag”) within the scope of the present invention. The interrogator is a transceiver facility with at least one antenna, which transmits an electromagnetic signal or field within a reading range. As soon as the object with the associated transponder comes into the reading range of the interrogator and an antenna of the transponder receives the electromagnetic signal transmitted by the interrogator, a transmitter of the transponder is stimulated to emit a response signal. This in turn is detected, decoded and converted by a receiver of the interrogator. Usually the response signal from the transponder is a signal modulated with the interrogator&#39;s transmitted signal according to a mathematical relation. In applications where, in addition to simple position determination for the moving objects, an identification and subsequent sorting of the objects is also required, superposing the response signal on information personalizing the transponder is also known. In this way the interrogator receives information not only about the positions of the objects, but also about their individual order. 
     A problem with this method is that the transponder&#39;s response signal is dependent on an individual response sensitivity and a spatial orientation of the transponder relative to the interrogator antenna. This makes the locating of the transponder and/or the objects imprecise. This effect can lead to objects close beside one another not getting resolution, so that their order is incorrectly detected and sorting errors then follow. 
     A first approach to solving this problem involves evaluating the amplitude of the reverse modulated response signal from the transponder. For this, the peak value of an amplitude characteristic is usually assigned to the spatial center of the interrogator antenna&#39;s reading range. However, since depending on the transponder&#39;s orientation the amplitude peak value need not necessarily match the spatial center of the interrogator&#39;s reading range, this too can lead to imprecise position determination and sorting errors. For this reason it is not possible to distinguish transponders closely following one another. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is therefore based on the object of providing a method for locating moving objects that permits high precision in position determination and thereby largely eliminates sorting errors. A device suitable for executing the method is further supplied. 
     According to the invention this object is achieved with a method having the characteristic features as claimed in claim  1  and a device as claimed in claim  10 . Since an interference pulse influencing the transponder&#39;s response signal is exerted on at least one defined location within the interrogator&#39;s reading range, and a position of the object is determined in dependence on a time when the influence of the response signal occurs, the precision of locating is clearly increased compared to known methods. Within the interrogator&#39;s reading range, the interference pulse to be defined later in more detail marks a location that can be correlated with great precision with the occurrence of a disturbance of the transponder&#39;s response signal, in particular an erratic discontinuity of the response signal. In other words, it may be assumed with great reliability that at the time at which the influence of the response signal is detected by the interrogator, the transponder or the object concerned is at the defined location of the disturbance. In this way even objects close beside one another can be detected and sorted with sufficient precision. 
     According to an advantageous embodiment of the invention, the interference pulse is a mechanical pulse, which causes an interference movement of the object superposing the movement of the object. For example, within the object&#39;s path of movement, and in particular within a conveyor belt, a step can be arranged that causes a tilting movement of the object and the transponder, thereby briefly altering an orientation of the transponder in relation to the interrogator. Since the transponder&#39;s response signal, particularly its amplitude, depends on the transponder&#39;s orientation, the object&#39;s interference movement developed here as a tilting movement causes a discontinuity in the characteristic of the amplitude of the response signal. The mechanically caused interference movement can likewise be a turn and/or a change in direction of the object, which is effected by corresponding turning or direction-changing arrangements disposed within a conveyor section. Alternatively or additionally, the interference movement can also be a vibration of the object, caused by a mechanical shaking of the object occurring at the location of the disturbance and/or by an acoustic sound acting on the object. 
     In an alternative advantageous embodiment of the invention, the interference pulse influences the electromagnetic field and/or a resonant frequency of the transponder at the defined location (location of the disturbance) within the interrogator&#39;s reading range. Accordingly, the interference pulse can for example be a local change of temperature, a magnetic influence exerted by a correspondingly arranged metal, a shielding measure or field routing measure affecting the electromagnetic field and/or a change of a dielectric constant and/or permeability of a surrounding medium or similar. 
     A further advantageous embodiment provides that the transponder&#39;s response signal contains information personalizing the transponder. This can be provided in particular in the form of a transponder-specific carrier frequency. The provision of such personalizing information is always necessary when the objects should not only be located, but also identified and sorted. 
     The method according to the invention and the device according to the invention can be used especially advantageously for locating and sorting objects on conveyor belts. In particular, items of luggage on conveyor belts in airports or packages on assembly lines can be located, and sorted and transported on to their individual destinations. The method is further suitable for locating and/or sorting moving objects on assembly lines in production processes. 
     Further preferred embodiments of the invention arise from the other features cited in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be further described with reference to examples of embodiments shown in the drawings to which, however, the invention is not restricted, in which: 
         FIG. 1  shows a device and a method for locating moving objects according to the prior art, and 
         FIG. 2  shows a device and a method for locating moving objects according to an advantageous embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows in the upper part of the diagram a number of differently shaped and oriented objects  12 , which are moved on a conveyor belt  14  in the direction of the arrow. A device for locating the moving objects  12  is marked altogether as  100 . The device  100  includes an interrogator  16  arranged in a stationary position, being essentially a transceiver facility. Shown here is just one antenna  18  of the interrogator  16 , which serves for transmitting and receiving an electromagnetic signal or field. Different from the representation, several differently arranged interrogator antennas  18  can also be provided. The device  100  further includes transponders  20 , of which at least one is arranged on each object  12 . 
     The interrogator  16  or the antenna  18  transmits a transmit signal, in particular a high-frequency signal, within a reading range, which essentially extends vertically below the area bounded by the antenna  18 . As soon as a transponder  20  of an object  12  enters the reading range of the interrogator  16 , the transmit signal is received by an antenna, not further shown, of the transponder  20 , whereupon a transmitter, not shown either, of the transponder  20  transmits a response signal modulated with the transmitted signal. This response signal can advantageously contain transponder-specific information, in particular in the form of an individual carrier frequency, which enables identification of the different objects  12 . An evaluation facility assigned to the interrogator  16 , and not shown, processes the received response signal, for instance in order to appropriately drive sorting facilities (not shown) on the output side of the conveyor belt  14 . 
     Only position determination for the objects  12 , which is often inadequate, is possible with this known arrangement. This problem is explained in the lower part of  FIG. 1  with the help of time curves of the response signals reverse-modulated by the transponders  20 . The amplitude curve of the response signals from the transponders  20  over time Z is shown. The amplitude AT of a transponder response signal depends both on the distance of the transponder  20  from the interrogator antenna  18  and also on the spatial orientation of the transponder  20  relative to the antenna  18 . It depends primarily on a size of an area of the transponder  20  projected orthogonally on to the area of the antenna  18 . The nearer the transponder  20  is to the antenna  18 , and the larger the area of the transponder  20  “seen” by the antenna  18 , the greater is the amplitude of the transponder response signal. 
     In the example shown, the object A goes first through the reading range of the interrogator antenna  18 . Since the transponder  20   a  of the object A is on the side of the object turned towards the interrogator  16  and is thus relatively near to the antenna  18 , and the transponder  20   a  is facing the antenna  18  with its biggest possible area, the individual amplitude curve associated with the object A shows a relatively high intensity and also a symmetrical pattern. The response signal characteristic of the transponder  20   a  is evaluated by the evaluation unit of the interrogator  16 , a maximum of the amplitude curve usually being assigned to the spatial center of the interrogator antenna. Because of the optimal spatial orientation of the transponder  20   a  of object A, precise locating is possible here without problems. 
     In contrast, because of the oblique orientation of the corresponding transponder  20   b  to the antenna  18 , the amplitude curve for the reverse modulated response signal of the tetrahedral object B shows an asymmetrical and wide pattern. This makes the position determination of object B with the help of the maximum value of the amplitude curve considerably less reliable. Nevertheless, because of the sizeable distance from the transponder  20   b  of the object B to the neighboring transponders  20   a  and  20   c , an accurate determination of the order is achieved. 
     Determining the position and order of the objects C and D becomes problematic: their transponders  20   c  and  20   d  are arranged in close succession, and in addition are unfavorably aligned relative to the antenna  18 . The transponder  20   c  of object C, which comes into the reading range of the interrogator  16  before object D, is not “seen” at first by the antenna  18 , since the body of the object C shields the electromagnetic field of the reading range. Conversely, the transponder  20   d  of the object D is already stimulated and detected by the antenna  18  at a time when the object D itself is still essentially outside the reading range. Consequently, the maximum amplitude of the transponder  20   d  is determined before the maximum of the transponder  20   c . The objects C and D are therefore detected in reverse order as a consequence, and then incorrectly sorted. 
     This problem is solved with a device shown in  FIG. 2  according to the invention. The same reference labels are used in  FIG. 2  for the same elements as in  FIG. 1 , and not explained once more. The device  100  according to the invention for locating moving objects  12  includes, as well as the interrogator  16  and the transponders  20 , an interference generator  22 , which is arranged at a defined location at position X within the reading range of the interrogator  16  and exerts an interference pulse on the object  12 , so that the response signal of the transponder  20  is influenced. 
     In the example shown, the interference generator  22  exerts a mechanical interference pulse on the object  12  and is developed as a step at position X of the conveyor belt  14  or as an offset in height between two successively arranged conveyor belts  14 . An object  12 , which is being moved over the step  22 , executes a tilting movement at a certain time, at which an overweight occurs of an overhanging extent of the object  12  over the step  22  (see object C in FIG.  2 ). This tilting movement causes a change in the distance of the transponder  20  arranged on the object  12  from the interrogator antenna  18 , as well as its spatial orientation. As a result, the reverse modulated amplitude of the response signal changes erratically at precisely this time. This discontinuous irregularity in the amplitude characteristic noticeably superposes the continuous customary pattern caused by the linear movement of the conveyor belt  14  (see lower part, FIG.  2 ). According to the invention, with the help of customary mathematical algorithms the irregularity in each individual amplitude curve of the individual transponders  20  is now determined and the time of occurrence of the irregularity is correlated with the position X of the step  22 . In other words it is assumed that at the time when the irregularity occurs in the response signal of the transponder  20 , the associated object  12  has its spatial center at the position X. 
     As can be recognized especially from the amplitude curves of the response signals of transponders  20   c  and  20   d  of objects C and D, a correct determination of position and order is also achieved for objects  12  whose transponders  20  are arranged close to one another. According to the principle, no minimum distance need be provided between neighboring transponders  20 . In this way a higher capacity level can be achieved for example in the case of assembly lines in production plants. It should also be stressed that even unintended field disturbances do not impair the reliability of the method according to the invention, as these equally affect all transponders  20  and are thus recognizable. 
     The principle of the interference pulse for simplifying locating according to the invention was explained in this case with the example of a mechanical interference pulse brought about by a step. It is understood, however, that mechanical interference pulses can also be generated in other ways, and that it is further possible to exert non-mechanical interference pulses too, which influence the electromagnetic field and/or the transponders&#39; resonant frequency at a defined position X within the reading range of the interrogator. Such interference pulses were already explained in the foregoing text. In any case, the interference pulse will influence the transponder&#39;s response signal erratically and thus enable precise position determination for the associated object. 
     Reference Label List: 
     
         
           100  device for locating moving objects 
           12  object 
           14  conveyor belt 
           16  interrogator 
           18  interrogator antenna 
           20  transponder 
           22  interference generator/step