MXPA00008534A - Identification of objects by a reader - Google Patents

Abstract

An identification system is provided for identifying a plurality of object-based transponders (14, 16, 18, 20) using an interrogator (10). The interrogator (10) includes a transmitter for transmitting an interrogation signal to the transponders, a receiver for receiving identification signals from the transponders, and processor means(21) for determining the individual and correct receipt of an identification signal. The transponders operate on the basis of backscatter modulation, and include a detector for detecting the presence of an interrupt signal from the interrogator. Control logic responsive to the detector is arranged to cease signal transmission from the transponder if the transponder completes transmission of the identification signal without receiving an interrupt signal during such transmission. The interrogator (10) is arranged to receive the identification signals from the transponders (14, 16, 18, 20) and substantially contemporaneously to determine if any identification signal has been individually and correctly received. In the event of any identification signal not being individually and correctly received, the interrogator (10), at substantially the same time, transmits a common interrupt signal for temporarily suspending signal transmission from the transponder (14) if the transponder is transmitting its identification signal at the time it receives the interrupt signal. The transponder (14) independently ceases signal transmission if it completes transmission of an identification signal without receiving an interrupt signal.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for the identification of objects, and in particular for the identification of a multitude of remote electronic identification cards by means of a reader that uses electromagnetic communication means. Numerous different types of electronic cards, which are typically in the form of an emitter, are attached to physical objects such as things, appliances, people, animals and the like. These cards are programmed to contain identification data, which are used to electronically identify the objects marked through questions by means of a reader. The information read is typically organized to be transferred to a computer system to count and read the identity of those objects that are in the interrogation area of the reader. A large number of patents covering the situation of a reader and a plurality of transmitter with the communication between the reader and the signal emitters are based on acoustic or electromagnetic radiation principles. In most cases, the prior art protocol requires that signal emitters have a unique identification number and the ability to receive and decrypt a transmission containing a flow of information from the reader and to counterpose it to all or the components of Your unique identification number. Another prior art class is an identification system that needs either a single identity or a multi-pulse receiver and a decoder for the signal transmitter, but which depends on the reader being in communication with the signal emitter in time. correct after the transmission has finished, if the signal transmitter was successfully identified. The communication can be in simple pulse format, and the message is communicated by the time of the communication after the transmission is finished, the communication can be as simple as a disturbance of an energy field from the reader at the right time. Such a system is described in the South Africa patent 92/0039, which requires the reader and the signal sender whose identity is being determined to be synchronized and to remain synchronized after the communication has been completed so that the reader You can respond at the correct time after the transmission has been completed. Another category of the prior art covers an identification system that uses a selection process to separate a simple signal emitter so that the information of the signal emitter can be received without having been altered by means of transmissions from other signal emitters. The patent US 5,751,570 describes said type of system. A collision signal is initially sent by the reader to place all signal emitters in an inactive state. Each signal emitter calculates a random inactive state after receiving the collision signal, during which they do not transmit their information. At the end of the inactive state each signal emitter will transmit its information again. If the reader receives information from only one signal transmitter, it sends a busy signal which puts all the signal transmitters in the unused state except the one that is busy transmitting. The issuers of signals in the unoccupied state do not transmit more information. After the reader receives the complete information from the individual signal transmitter, the reader transmits and recognizes the signal that the identified marker places in a passive or unoccupied state in which it stops transmitting its information. The rest of the signal transmitters in idle state are reactivated and they re-calculate a random idle time. The previous steps are repeated until all signal emitters have been identified. The disadvantage of this system is that if the electromagnetic field changes to send the busy signal, changes in the electromagnetic field can cause the receiver to misinterpret the information from the signal emitter because the signal from the signal emitter is much smaller than the changes in the electromagnetic fields. A similar system is described in US Patent 5,124,699, wherein changes in frequency are used to send signals to signal emitters. Initially a change in frequency is sent to the signal emitters to begin a selection process that will isolate an individual signal emitter. The signal emitters calculate a random delay after which they transmit a start block. Due to the random delay, only some of the signal transmitters can transmit a start block at the same time. When the reader receives a start block, the transmission frequency changes, which means that the transmitters do not transmit a start block to move to a passive state. The remaining signal transmitters transmit their unique code. If the reader detects that more than one signal transmitter is transmitting its code then the reader signals an error by means of a transmission frequency change which causes these signal transmitters to have to calculate a delay again at random and follow the previous steps. The senders of signals in the passive state remain that way. This selection process will eventually produce an individual signal emitter. Once the reader has identified the individual signal transmitter it is placed in a passive state by another frequency change which also causes the emitters of remaining unidentified signals to start the selection process again. This system needs a complex tone circuit in the signal emitter so that different frequencies can be detected.

COMPENDIUM OF THE INVENTION. According to a first aspect of the invention there is provided a method for identifying objects by means of an interrogator, comprising the steps of: Transmit an interrogation signal from the interrogator to the objects; The transmission from each object to the interrogator and the identification signal having predetermined indicator characteristics in response to the interrogation signal; Receive the identification signals from the objects in the interrogator and substantially simultaneously determine in the reader whether any identification signal has been individually and correctly received on the basis of the characteristics of the indicator; Transmit substantially contemporaneously from the interrogator a common re-transmission or interrupted signal in the event that any identification signal has not been individually and correctly received; Y Stop the transmission signal from an object if the object completes its transmission signal without having received a signal interrupted from the interrogator during said transmission. Preferably, the method includes the steps of temporarily suspending the transmission signal from an object if the object is transmitting its identification signal at the same time that it receives the signal interrupted from the interrogator. In a preferred form of the invention, the method comprises the other steps to continue in order to receive all identification signals in the interrogator, and to transmit the interrupted signals, until no other identification signal is individually and correctly received by a enough time to ensure that all identification signals from the objects have been individually and correctly received by the interrogator. In one form of the invention, the method may comprise the steps of continuously transmitting the interrogation signal and transmitting the interrupted signals in a time interval that is no less than the average of the transmission time of a valid identification signal in the absence of the reception of an identification signal in the interrogator. Conveniently, the method includes the steps of transmitting in random periods of time an identification signal from each object that has not stopped its transmission signal and that allows each object that has halted its transmission to recommence transmission in response in case of returning lets start. The restarting event may include the absence or variation in the interrogation signal by a predetermined minimum period of time. Advantageously, the method further includes the steps of transmitting an invalid signal from the interrogator, receiving the invalid signal in at least one of the objects, and establishing a memory element in order to prevent it, only after the object has stopped the transmit signal, to respond to any subsequent interrogation signal for a predetermined minimum period of inactivity time. The method can still include the steps of transmitting an invalid signal from the interrogator, receiving the invalid signal in at least one of the objects, and resetting the memory element in the object to deactivate the object and allow it to respond to it or Subsequent interrogation signal in the manner described above. Advantageously, valid and invalid signals are at least initially transmitted prior to the possible transmission from any object of an identification signal, and valid and invalid signals also serve as interrupted signals. Typically, the predetermined indicator characteristics of the identification signals are identical in form and have a predetermined duty cycle, and include a fixed flow of information duration preceded by an initial title and includes an information component and a control component of calculation, with the transmission of a signal from an object starting with the same title, and the interrogator is accommodated to accept the beginning of an identification signal only if transmission has not been received immediately prior to the reception of such title. The characteristics of the indicator may also include the transmission of the modified Manchester-shaped identification signal to combine the transmission clock rate and the information flow to produce a 50% duty cycle at a minimum operational bandwidth. The invention extends to an identification system comprising an interrogator and a plurality of object-based answering machines, the interrogator includes transmission means for transmitting an interrogation signal to the answering machines, receiving means for receiving the identification signals from the answering machines, and a processor means for determining the individual and correct receipt of an identification signal, each answering machine comprises a receiver for receiving the interrogation signal, generating means for generating the identification signal, a transmitter for transmitting the identification signal back to the interrogator , a detector for detecting the presence of a signal interrupted from the interrogator, and a control means that responds to the detector and accommodates to stop the transmission signal from the answering machine if the answering machine completes the transmission of the identification signal without have received a signal interrupted gone during said transmission. Preferably the control means is arranged to temporarily suspend the transmission of an identification signal from the answering machine if the answering machine is transmitting its identification signal while receiving the interrupted signal. Advantageously, the generating means comprises a first memory means for storing identification information, an oscillator, a Manchester encoder for deriving the coded identification information from the identification information and the oscillator, and a modulator driven by the Manchester encoder to derive a identification signal, and the transmitter and receiver comprise an antenna coupled to an RF module to effect backscattering modulation of the identification signal. Typically, the interrogator accommodates to continue to receive identification signals, and to transmit the interrupted signal, until no other identification signal is individually and correctly received for a sufficient period of time to ensure that all identification signals have been individually and correctly received by the interrogator. The identification system may include a processing means for generating the interrupted signals and for generating valid and invalid signals for respectively validating or invalidating the answering machines, and each of the answering machines includes a second memory mechanism organized to be placed by an invalid signal for prevent the answering machine from answering any subsequent interrogation signal from the interrogator for a predetermined minimum period of time, only after the transmission signal has finished, and to be reset by a valid signal to allow the answering machine to immediately respond to a signal of interrogation. According to yet another aspect of the invention, an answering machine for an identification system of the type comprising an interrogator and a plurality of answering machines is provided, each answering machine comprises a receiver for receiving an interrogation signal, a first memory mechanism for storing identification information, an oscillator, a modulator for deriving a modulated identification signal from the identification information and the oscillator, and a transmitter for transmitting the identification signal back to the interrogator, the answering machine further comprises a detector for detecting the presence of a signal interrupted from the interrogator, and a finished signal mechanism organized to stop the transmission signal from the answering machine if the answering machine completes the transmission of the identification signal without receiving a signal interrupted from the interrogator during said transmission. The answering machine advantageously includes a mechanism for suspending signals that responds to the detector and has been temporarily arranged to suspend the transmission of an identification signal from the answering machine if the answering machine is transmitting its identification signal while receiving the interrupted signal. Typically, the mechanism for suspending a signal and the mechanism for stopping a signal are incorporated into the logic control circuit, the answering machine further includes a random chronometer connected to the control logic circuit to enable the identification signals to be repeatedly re-transmitted. in different random time intervals from the answering machine until the transmission of an identification signal has been completed without having been interrupted by an interrupted signal. Conveniently, the answering machine includes a second memory mechanism organized to be placed by an invalid signal to prevent the answering machine, only after the answering machine has completed the transmission signal, to answer any subsequent interrogation signal for a predetermined minimum period of time . The second memory mechanism can be placed to be reset by a valid signal to allow the answering machine to answer a subsequent interrogation signal after the answering machine has completed the transmission signal. Typically, the second memory mechanism comprises a register that responds to invalid signals and a memory module that responds to both the register and the completed signal mechanism to allow the answering machine to complete the transmission of an identification signal prior to being disabled. Advantageously, the answering machine further includes a Manchester encoder for deriving the coded identification information from the identification information and the oscillator, for receiving in the modulator, and the transmitter and receiver comprising an antenna coupled to an RF module for effecting a backscatter modulation. in response to the interrogation signal, the encoder Manchester responds to a valid output signal that represents that the transmission of the identification signal is complete. According to yet another aspect of the invention, an interrogator for an identification system of the type comprising an interrogator and a plurality of answering machines is provided, the answering machine includes a transmission mechanism for transmitting an interrogation signal to the answering machines, the receiving mechanism for receiving the identification signals from the answering machines in response to the interrogation signal, a first processing mechanism for substantially simultaneously determining the individual and correct reception of an identification signal, a signal generating mechanism responding to the processing mechanism to generate substantially simultaneously a signal interrupted in the event that any identification signal has not been individually and correctly received from any one or more objects, and to cause the interrupted signal to be transmitted fast enough to suspend the signal d e transmission from any object at the time that its identification signal was not individually and correctly transmitted. Preferably, the first processor mechanism is placed to continue receiving and processing all identification signals, and the signal generating mechanism is set to continue generating interrupted signals, until no other identification signal is individually and correctly received, for a period of time. enough time to ensure that all identification signals from the objects have been individually and correctly received. Typically, the transmitter is placed to transmit the interrogation signal continuously, and the signal generating mechanism is placed to transmit the interrupted signal in a period of time that is still less than the average time received from an identification signal in absence of the reception of an identification signal in the interrogator. Conveniently, the generating mechanism of signals is placed to generate valid and invalid signals to be transmitted by the transmitter, the invalid signal is accommodated to place the memory elements in the objects to prevent them from that, only once they have finished the signal of transmitting, responding to any subsequent interrogation signal by a predetermined minimum stopping time period, and the valid signal is placed to reset the memory elements to allow the objects to respond to a subsequent interrogation signal.

The receiver may include a receiving antenna a quadrature receiver, and the first processor mechanism may include a signal processor for processing a baseband of components of the identification signal derived from a speech receiver to a reconstructed Manchester information signal, and a microprocessor to check errors to decode and check errors in the Manchester signal at least on the basis of the duty cycle, clock speed, information flow duration and a calculation sum check.

BRIEF DESCRPTION OF THE FIGURES Figure 1 shows a reader and 4 signal emitters of the invention in the electromagnetic field of the reader; Figure 2 shows a schematic block diagram of the reader of the invention; Figure 3 shows a schematic block diagram of a signal emitter of the invention; Figure 4 shows a series of signals in the form of waves illustrating the communication protocol between the reader and the signal emitters; Figure 5 shows a schematic diagram of a typical identification signal successfully transmitted; Y Figure 6 shows a flow chart illustrative of the logic control operation of the signal emitter.

DESCRIPTION OF THE MODALITIES Figure 1 shows a reader or interrogator 10 which transmits an energized magnetic field represented by an oval footprint 12. The oval footprint 12 represents the effective reading range of the reader, which is typically between 4 to 6 meters. Four signal emitters 14, 16, 18 and 20 are within the field. Any signal emitter within the footprint 12 will generate enough energy from the energized field in order to give power to its circuit. In this situation in which signal emitters are using energy from an energized field to power their electronic circuit, and due to the fact that the field that is needed to energize is typically stronger than the field strength needed to communicating using the backscatter modulation method, it can be accepted that all signal emitters that have been energized by a reader will have quality of communication with the reader and that their reflected backscatter signal will be received by the reader. When signal emitters leave the zone, they lose power and stop operating before their communication signals degrade to such a level that the reader is no longer able to correctly receive all backscatter signals. Initially the energized field is not operating. The mode of operation is regulated by a computer 21 connected to the reader. The modes of operation are "normal reading" without an electronic surveillance article (EAS) after the signal emitters are successfully identified, "set EAS on" to disable each signal emitter once it has been successfully identified, and "eliminate EAS "to enable each signal transmitter before reading. The electronic surveillance article is commonly used as a measure of anti-theft in stores and anti-"reduction". The energized field is turned on, the signal emitters are identified and then it is switched off again. Figure 2 shows a schematic block diagram of a reader 10. An oscillator 22 provides a wave signal transporter at a typical operating frequency of 915 MHz. A modulator 24 is controlled by a microprocessor 26.

This allows the microprocessor 26 to send signals to the signal emitters by modulating the wave signal transporter. The signals are sent by the microprocessor 26 by changing the modulator 24 to a 100% modulation depth for a short period (100μsec) which has the effect of sending a negative output pulse to the signal emitters. Another method may be to transmit an independent signal on another frequency, to increase the force level of the energized field, or to transmit the energized field briefly with another polarization. The different types of interrupted signals sent to the signal emitters are a "normal interrupted" signal consisting of a single pulse, an "established EAS interrupted" signal consists of two pulses and an "EAS-free" signal consists of five pulses, which must be sent within 16 meters after the energized field has been turned on.

The interrupted signals are communicated by the same means to all signal emitters, regardless of whether they are transmitting at that moment. These 'signals are interpreted at the same time that the unsuccessful transmission signal for those signal transmitters are currently in a transmission state. The interrupted signal is transmitted at the instant the reader detects a corrupted transmission state, and is not necessarily synchronized with any clock information in any signal transmitter. A power amplifier 28 increases the modulated carrier wave signal to sufficient levels to give an effective reading range 12. A transmitting antenna 30 emits the carrier wave signal to give an energized field, and the signal emitters 14, 16, 18 and 20 derive power from the energized field and transmit their codes by means of backscatter modulation. A receiving antenna 32 receives the backscattered modulation signals reflected from the signal emitters. The received backscatter modulation signals are mixed with the local oscillator signal 34 in a quadrature receiver 36. A local oscillator signal 34 is derived from the oscillator 22. The output of the quadrature receiver 36 is a baseband signal 138 and a baseband Q signal 40 which represents the information emitted. The signal 138 and the signal Q 40 are fed into a signal processing module 42. The signal processing module 42 amplifies the signals, and "combines them together to give a reconstructed Manchester information signal sent by the signal emitters. combination of signal I 38 and signal Q 40 allows the code of the signal transmitter to be detected regardless of the length of the path between reader 10 and signal emitters 14 and 20. The reconstructed Manchester information signal 44 is entered into the microprocessor 26 to be decoded and to check for errors The transmitter information is encoded in a modified form of Manchester where the transmitter clock speed, typically 10 KHz, and the serial information are combined to give a flow of information that has a 50% duty cycle in a minimum operational bandwidth From this information flow it is possible for the microprocessor 26 to extract the information rmation and the clock speed of the transmitter. The microprocessor 26 performs an error check to determine, first if there is more than one transmitter transmitting at the same time and second, if only one transmitter is transmitting, if there are errors in the received information received. In both cases, the senders or sender respectively send an interrupted signal if the microprocessor 26 finds an error so that the senders can retransmit their information. The clock speed of the emitters is typically 10 KHz with a tolerance of 20% that is, the clock speed of an emitter can vary from 8 KHZ to 12 KHz. The microprocessor 26 checks that the emitter's clock speed is between these two predetermined limits, which will not allow an interrupted signal to be transmitted. The coded Manchester information flow, which is shown at 45 in Figure 5, is a fixed-length information flow, which in this mode is 81 pulses. Any prolonged duration of the code means that more than one sender is communicating at the same time and that the reader is detecting a corrupted signal. The microprocessor 26 checks the duration of the information flow and if more than 81 pulses are received, an interrupted signal is transmitted. All transmitter transmissions will start with the same starter pulse 45 At the front of the Manchester information. The microprocessor 26 needs no transmissions received immediately before the initial transmission to clearly define the start of the transmission, which is signaled by 3 clock periods 45 B of lOKHz ie 300μsec. If there are transmissions in this period, an interrupted signal is transmitted. After the holder 45A, the information issued is in the form of a row of pulses 45C followed by a calculation check or parity component 45D allowing the microprocessor 26 to verify that the received information is correct, verifying that the parity or calculation check provides the correct answer and that the information has not been contaminated by a simultaneous transmission made by a second emitter that has the same starting time and the same transmitter clock speed. If the calculation chuequeo or parity of calculation provides an incorrect answer, an interrupted signal is transmitted. During transmission the clock speed of any transmitter will be stable and the microprocessor will be able to monitor this stability as it is transferred in the information flow, and determine as soon as there is any sudden change in the clock speed in the information flow. as what can happen when another transmitter begins its simultaneous transmission. The microprocessor monitors the clock speed of the information flow and any change in the received clock speed that will cause an interrupted signal to be transmitted. If the information flow passes all the above tests, the microprocessor 26 has decoded an information issued from a simple transmitter. This information is sent to a computer 21 through a communication loop 46 to be processed later. In this mode, the communication loop is a RS232 serial connection. This can also be a parallel connection or a network connection. The incorporation of a unique identity number in the information issued is not one of the properties necessary to successfully receive information from issuers. The system will operate when many issuers have identical numbers, in which case it will be able to count how many times such numbers were found. Figure 3 shows a schematic block diagram of a transmitter 48. The emitted information or code is stored in an information memory module 50. In this mode the information emitted consists of 80 pulses and a head pulse 1. The memory information it is preferably PROM memory, but EPROM or EEPROM memories can also be used. It is preferably programmed when the emitter is applied to the object that is identified. The programming is carried out by a programmer which has two direct contact hooks on an antenna 52 to provide power and a third direct contact hook in a programming booklet 54 for the information broadcast. The antenna 52 collects energy from the energy field 12. The antenna is a dipolar wire antenna. A piece of brass antenna can also be used. A radio frequency (RF) module 56 rectifies the accumulated energy and charges a nergia store in the form of a capacitor 57 to provide the operating voltage for the emitter circuit. A small battery can also be used to power the transmitter. The closer the reader's transmitter is, the stronger the energy field and the greater the accumulated energy.

The RF module 56 also has an overvoltage protection in the form of a zener type 57A diode component to limit the operating voltage when the emitter is near the reader. When the energized field is turned on, the emitter circuit is capacitated. An oscillator 58 provides an imprecise but stable clock signal 60 for an emitter circuit in the range of 8 KHz to 12 KHz, typically 10 KHz. A logic control unit 62 divides the clock at 81 to provide a clock frame signal. A frame is defined as the number of cycles that the clock transmits the entire emitted information of 81 pulses, so that the clock frame takes effect every 81 clock cycles or 8.1 ms for a 10 KHz oscillator. The clock cycle signal 64 is used to register a delay counter 66 at random. The random delay counter consists of a random pseudo-number generator 68 and a counter 70. When the transmitter is turned on, the meter 70 is always loaded with the number two so that the transmitter will always transmit its information in the third. frame after power-up so that if it is the only emitter present it can be quickly identified. The counter 70 counts upside down and when it reaches 0 it generates an activating signal 72. The triggering signal 72 causes the random pseudo-number generator 68 to calculate a new random number which is then loaded into the counter 70 to record the next period of random delay. The triggering signal 72 also causes the signal emitter to begin transmitting its information which occurs in the following manner. The logic control unit 62 sends a clock signal change 74 to the information memory module 50 which serially changes the information 76, starting with the start pulse, out of the information memory module 50. The information 76 is exclusive with the clock 60 in a Manchester 78 encoder. The logic control also enables the performance of the Manchester 78 encoder by means of a valid output signal 80. The performance of the Manchester encoder 78 drives a modulator 82. The modulator 82 changes the load on the antenna and modulates the backscatter from the antenna with Manchester encoded emitted information. At the next clock frame signal 64 the transmission of the information is terminated and the rendition of the encoder Manchester 78 is disabled by means of the valid output signal 80. When the reader 10 sends a signal to the emitter it momentarily removes the RF energy. say, it drives the energy out of service and puts it back again. A pulse detector 84 continuously monitors the RF energy that arrives at the antenna 52 by pulses from the reader 10. The number of pulses are counted. If a single pulse is received a "normal interrupted" signal is modulated. If a double pulse is received the signal 88"EAS interrupted" is modulated in a memory device in the form of an EAS 89 recorder. If five pulses are received a signal 90"Clear EAS" is modulated to clear the recorder 89. The "Clear EAS" signal is only monitored during the first two frames after power-up, after which it is ignored. When any pulse is received from the reader that is, if any of the interrupted signals 86 or 88 is modulated while the transmitter is busy transmitting its information, the output information of the Manchester encoder 78 is immediately disabled by means of the output information of the encoder. the enabled signal 80. This immediately stops the modulation of the antenna and thus stops the backscatter modulation. If, however, the transmitter is capable of transmitting its complete information without receiving a pulse or pulses from the reader 10, the transmitter "knows" that it has been successfully identified by the reader 10. The logical control 62 places the transmitter in a state passive in which it stops transmitting any other information until it has been reset by removing the field -energized. Another method of resetting the transmitter may be a modulated tone on the conveyor. If a "set of interrupted EAS signals" 88 are received before the transmitter successfully transmits its information, then an EAS 89 recorder in the logic control unit is set so as to remember that the EAS mode must be enabled when the transmitter has successfully transmitted its information. In this way, when the transmitter successfully transmits its information and the EAS recorder is established, an EAS 92 memory module is established and thus the transmitter is placed in the EAS mode. The EAS 92 memory module maintains its status even when the power is removed from the transmitter. If the EAS 92 memory is set, then the transmitter is disabled to transmit its information. An interrupted EAS signal set has to be received by the transmitter prior to the transmitter transmitting its identification signal for the first time so that the EAS recorder can be established prior to the first transmission, thus ensuring that, in the In case that only one transmitter is located in the footprint of the interrogator, the identification signal from the transmitter is located. More particularly, if the identification signal from a single transmitter is successfully transmitted without generating an interrupted signal, the EAS recorder could not be activated. As a result a "false" interrupted signal is initially sent to ensure that despite all the EAS register is activated, as shown by the interrupted signal 88A in Figure 4. The EAS 92 memory module is a medium memory element. term with a typical constant time of several hours, which operates to block any transmission of backscatter modulation while the memory is established. This memory element has dispersion and will reset after its charge has been dispersed, which is typically from four to eight hours, depending on the ambient temperature. This operation works independent of the transmitter having power from its presence in an energized field. If an EAS 90 clear signal is received during the first two frames after power up, the contents of the EAS 92 memory module are cleared independent of whether it has been set or not and thus the transmitter is re-enabled to transmit its information again . Figure 4 shows the interaction of a waveform signal between the reader 10 and the transmitters 14 to 18. The waveforms 10B and 10C show the energized field of the reader 10 for three different options. The waveform 10A is for the case in which "normal interrupted" signals are used, the waveform 10B is for the case when the "interrupted EAS signals" are used and the 10C waveform is for the case when the signal "EAS cleared" is initially sent to clear the EAS 92 memory modules, followed by "normal interrupted" signals. The waveforms 14A, 16A, 18A and 20A are the output signals of the Manchester encoder i.e. the modulation of the antenna 52 of the respective transmitters 14, 16, 18 and 20. In time to the reader 10 turns on the field energized 12. The transmitters are energized and carry out a reset. At time ti, typically 4ms, the reader sends a signal interrupted prior to the first transmission of the transmitter. For waveform 10A an interrupted normal signal 86A is sent which has no effect on the transmitters. For waveform 10B a set of "EAS signal" 88A is sent which causes the signal set EAS 88 in the transmitters to be modulated and the logic control relay EAS 62 to be set. For the 10C waveform a "cleared EAS" signal 90A is sent which causes the clear signal EAS 90 in the transmitters to be modulated and the logic control 62 to clear the EAS 92 memory, thus allowing the transmitters to transmit your information again.

At time t2, typically 16 ms, all transmitters have waited two frames after power up and they start transmitting their respective information. The random delay timer 66 on the transmitters are started with new random delays. The reader 10 receives the backscatter modulations 14B to 20B from the transmitters and tries to reconstruct the Manchester information. As there is more than one transmitter 14 to 20 transmitting, the microprocessor 26 will detect an error in the reconstructed information Manchester so that at time t it sends an interrupted signal modulating the energized field. The pulse detectors of the transmitters 84 detect the pulse (s) in the energized field and modulate the relevant signal. In the case of waveforms 10A and 10C the interrupted normal signal 86 is modulated and in the case of the waveform 10B, the "EAS signal set" 88 is modulated. The logic control 62 immediately disables the output signal from the Manchester 78 encoder and in this way the transmission of information from the transmitters is stopped. The transmitters wait their respective delay times.

At time t4 the random delay timer 66 of the transmitter 14 generates the activated signal 72 which causes the transmsior 14 to begin transmitting its information 94. The reader receives the backscatter modulation 94 and tries to reconstruct the Manchester information. The microprocessor 26 decodes the Manchester information while - checking for errors. As there is only one transmitter, the information will not have errors and in this way the microprocessor does not send an interrupted signal. Once the transmitter 14 has finished transmitting its information and pulses are not received from the transmitter, the logic control 62 of the transmitter 14 places the transmitter 14 in a passive state and stops any transmsion for the duration of the interrogation signal. The microprocessor 26 sends the transmitted information and has been successfully received to the computer 21 through the communication loop 46. At time t5 the random delay timer 66 of the transmitter 18 generates an activated signal 72 which makes the transmitter 18 begin to transmit your information 96. Reader 10 receives the backscatter modulation and tries to reconstruct the Manchester information. The microprocessor 26 decodes the Manchester information, while checking for errors. At time t6 the random delay timer 66 of the transmitter 20 also generates the activated signal 72 which causes the transmitter 20 to also begin transmitting its information 98. The microprocessor 26 detects an error in the reconstructed Manchester information so that at time t7 sends the interrupted signals 86 or 88 modulating the energized field. The pulse detectors of the transmitter 84 detect the pulses in the energized field and the relevant interrupted signal 86 or 88 is modulated. The logical control unit 62 of the transmitter 18 and 20 immediately disables the output signal from the Manchester encoder 78 of the transmitters 18 and 20 and thus the transmission of information from the transmitters 18 and 20 is stopped. The transmitters 18 and 20 await their respective delay times determined by their random delay timers 66. At times t8, t9, and t? O the transmitters 16, 20 and 18 respectively transmit their respective information 100, 102 and 104 without interruptions and thus are successfully received by the reader 10 and sent to the computer 21. The transmitters 16, 18 and are placed in a passive state and stop transmitting. Once the receiver 36 does not receive any other information for a period equal to the longest random delay timer of the transmitters (in this case 2 seconds) it indicates to the computer 21 that all the transmitters are read and deactivates the energized field 12.

Referring to Figure 6, it shows an explanatory flow chart itself indicates the operation of a logic control unit 62. In particular, the flow chart is illustrative of the manner in which the different EAS modes operate. For modeling purposes, for emitters with an IOKHz clock speed, and a transmission frame time of 128 in a maximum random period, for 400 transmitters to be read, more than 30000 collisions (or interruptions) may occur in the reading of the issuers. If a reader is in the process of radiating an energized field and for some reason does not want to accept more identities, for example, while waiting for the computer to clear its accumulation, the reader can generate interrupted signals in the period less than the time transmits a message for the fastest possible clock transmission and thereby prevents senders who are not yet in a passive mode from entering a passive mode until the block has been cleared. The above mode is suitable for applications where a number of transmitters are placed in the reading range of the reader, the energized field is turned on, the emitters are read and the energized field is turned off again. In situations where the reader is mounted, for example, in a door frame for access control or on a conveyor belt, the energized field can be permanently lit and the emitters can be moved to the energized field, they can be activated, transmit your information and then move out of the energized field again. In these situations the reader can continuously transmit interrupted signals in a smaller interval than the transmission time of a message for the fastest allowed stopwatch, typically 5 ms. The reader stops sending interrupted pulses only when it begins to receive information transmitted uncorrupted from a particular transmitter and continues suspending transmissions of such interrupted pulses for the time in which the information remains uncorrupted until the transmitter completes its transmission successfully. Subsequently, it continues to send interrupted signals at 5 ms intervals until it begins receiving uncorrupted transmitted information from another sender. In this way the transmitters can be moved past a permanently activated reader, which will be able to read them and will still be able to process multiple transmitters. Also, and because the transmitter only transmits after a period of two frames (typically 16 ms) the sender can receive at least two interrupts of the "interrupted EAS set" type, if an EAS mode is needed, prior to its first transmission, thus satisfying the need to enable an EAS.

Claims (26)

R E I V I N D I C A C I O N S

1. A method for identifying objects by an interrogator, comprising the steps of: transmitting an interrogation signal from the interrogator to the objects; transmitting from each object to the interrogator an identification signal having predetermined indicator characteristics in response to the interrogation signal; receiving the identification signals from the objects in the interrogator and substantially contemporarily determining in the reader whether any identification signal has been individually and correctly received on the basis of the characteristics of the indicator; substantially contemporaneously transmitting from the interrogator a common signal re-transmitted or interrupted in the event that the interrogator detects a corrupt transmission state resulting from any identification signal that has not been individually and correctly received; and independently stopping the transmission of a signal from an object if that object successfully completes its signal transmission without receiving a signal interrupted from the interrogator during said transmission.

2. A method according to claim 1, which includes the steps of temporarily suspending the transmission signal from an object if that object is transmitting its identification signal while receiving the signal interrupted from the interrogator.

3. A method according to any of claims 1 or 2, further comprising the steps of continuing to receive all identification signals in the interrogator, and generating the interrupted signals in response to a corrupt transmission state, until there are no more signals individually and correctly received for a period of time sufficient to ensure that all identification signals from the objects have been individually and correctly received by the interrogator, the period of time being at least as long as a maximum period of time of a random internal transmission of any of the objects.

4. A method according to any of claims 1 or 2, comprising the steps in an alternative mode of operation of continuously transmitting the interrogation signal and transmitting the interrupted signals in a time interval that is still less than the average time of transmission of a valid identification signal in the absence of having received an identification signal in the interrogator.

5. A method according to any of claims 1 to 4, which includes the steps of transmitting in random time intervals an identification signal from each object that has not stopped its transmission signal and allows each object that has stopped its transmission restart your transmission in response to a reset case.

6. A method according to claim 5, wherein the reset event includes the absence of or variation in the interrogation signal by a predetermined minimum period of time.

1 . A method according to any of the preceding claims, which includes the steps of transmitting an invalid signal from the interrogator, receiving the invalid signal in at least one of the objects, and establishing a memory element in order to prevent it, only after the object has stopped its transmit signal, to respond to any subsequent interrogation signal for a minimum predetermined period of inactivity.

8. A method according to claim 7, which includes the steps of transmitting a valid signal from the interrogator, receiving the valid signal in at least one of the objects, and resetting the memory element in the object to enable the object and allow which responds to a subsequent interrogation signal in the manner described in claim 1.

9. A method according to claim 8, wherein the valid and invalid signals are at least initially transmitted prior to the possible transmission from any object of an identification signal, and wherein the valid and invalid signals also serve as interrupted signals.

10. A method according to any of the preceding claims, wherein the predetermined indicator characteristics of the identification signals are identical in shape and have a predetermined duty cycle, and include a fixed-length information flow preceded by an initial owner and includes an information component and an addition check component, with the transmission of a signal from an object starting with the same owner, and the interrogator is accommodated to accept the beginning of an identification signal only if it has not been received transmission immediately prior to the receipt of such holder.

11. A method according to claim 10, wherein the characteristics of the indicator further includes the transmission of the identification signal in a modified form of Manchester to combine the clock rate of the transmission and the information flow to produce 50% of performance cycle in a minimum operational bandwidth.

12. An identification system comprising an interrogator and a plurality of object-based answering machines, the interrogator includes means for transmitting an interrogation signal for the answering machines, receiving means for receiving the identification signals from the answering machines in response to the interrogation signal, means for processing to determine whether the identification signal is individually and correctly received or not and to generate a signal interrupted in the case of a failed transmission that is received from any one or more answering machines, each answering machine comprises a receiver to receive the interrogation signal, identification signal generating mechanism for generating the identification signal, a transmitter for repeatedly transmitting the identification signal back to the interrogator, a detector for detecting the presence of a signal interrupted from the interrogator, and a control mechanism sens ible to the detector and that is independently arranged to stop the transmission signal from the answering machine if the answering machine completes the transmission of the identification signal without having received a signal interrupted during such transmission.

13. an identification system according to claim 12, wherein the control means is temporarily accommodated to suspend the transmission of an identification signal from the answering machine if the answering machine is transmitting its identification signal while receiving the interrupted signal .

14. An identification system according to any of the preceding claims 12 to 13, wherein the interrogator is accommodated to continue receiving identification signals, and to continue transmitting the interrupted signal in response to a failed transmission signal, until no other signal identification is individually and correctly received for a sufficient period of time to ensure that all identification signals have been individually and correctly received by the interrogator, the time period is at least as long as a maximum random time period of an internal transmission of any of the answering machines.

15. An identification system according to any of the preceding claims 12 to 14, wherein the interrogating processor mechanism is further arranged to generate valid and invalid signals for respectively enabling and disabling the answering machines, and each of the answering machines includes a first mechanism of memory for storing identification information, a second memory mechanism accommodated to be established by an invalid signal to prevent the responder from answering any subsequent interrogation signal from the interrogator for a predetermined minimum period of time, only after the completion of the transmit signal, and to be reset by a valid signal to allow the answering machine to respond immediately to an interrogation signal.

16. An answering machine for a type identification system comprising an interrogator and a plurality of answering machines, each of the answering machines comprises a receiver for receiving an interrogation signal, a first memory mechanism for storing identification information, an oscillator, a modulator for deriving a modulated identification signal from the identification information and the oscillator, and a transmitter for repeatedly transmitting the identification signal back to the interrogator, the answering machine further comprises a detector for detecting the presence of a signal interrupted from the interrogator, and a mechanism to stop the arranged signal to stop the transmission signal from the answering machine if the answering machine completes the transmission of the identification signal without having received a signal interrupted from the interrogator during such transmission and a mechanism to suspend signal sensitive to the detector and that it is temporarily accommodated to suspend the transmission of an identification signal from the answering machine if the answering machine is transmitting its identification signal while receiving the interrupted signal.

17. An answering machine according to claim 16, wherein the mechanism for suspending signal and the mechanism for stopping signal are incorporated in the logic control circuit, the answering machine further includes a random chronometer connected to the logic control circuit to enable the signals of identification to be repeatedly retransmitted at different random time intervals from the answering machine until such time as the successful transmission of an identification signal has been completed without it having been interrupted by an intermittent signal.

18. An answering machine according to any of claims 16 or 19, which includes a second memory mechanism arranged to be placed by an invalid signal to prevent the answering machine, only after the answering machine has stopped the transmission signal, from responding to any subsequent Question mark for a minimum predetermined period of time.

19. An answering device according to claim 18, wherein the second memory mechanism is arranged to be reset by a valid signal to allow the answering machine to answer it or a subsequent interrogation signal after the answering machine has stopped the transmission.

20. An answering machine according to any of claims 18 or 19, wherein the second memory mechanism comprises a recorder responsive to invalid signals and a memory module responsive to both the recorder and the mechanism for stopping the signal to allow the answering machine to complete the transmission of an identification signal prior to being disabled.

21. An answering machine according to any of claims 17 to 20, further including a Manchester encoder for deriving encoded identification information from the identification information and the oscillator, for receiving it in the modulator, and the transmitter and receiver comprising an antenna coupled to an RF module for carrying out backscattering modulation in response to an interrogation signal, the Manchester encoder is responsive to a valid output signal which means the complete transmission of an identification signal.

22. An interrogator for a type identification system comprising an interrogator and a plurality of object-based answering machines, the interrogator includes a transmitting means for transmitting an interrogation signal to the answering machines, receiving means for receiving the identification signals from the answering machines in response to the interrogation signal, a first processing mechanism to substantially simultaneously determine the correct and individual reception of an identification signal, a signal generating mechanism responsive to the first processing mechanism to generate substantially simultaneously a signal interrupted in the event that any signal identification is not individually and correctly received from any one or more answering machines, and to cause the interrupted signal to be transmitted fast enough to suspend the transmission signal from any answering socket while there is no transmitted individually and correctly his identification signal.

23. An interrogator according to claim 22, wherein the first processor mechanism is accommodated to continue receiving and processing all identification signals, and the signal generating mechanism is arranged to continue generating interrupted signals, until no other identification signal is detected. individually and correctly received, for a sufficient period of time to ensure that all identification signals from the objects have been individually and correctly received.

24. An interrogator according to claim 22, wherein the transmitter is accommodated in an alternative mode of operation for continuously transmitting the interrogation signal, and the signal generating mechanism is accommodated to transmit the interrupted signal in a time period that does not stop of being less than the average time received from a valid identification signal in the absence of receiving an identification signal in the interrogator.

25. An interrogator according to any of the preceding claims 22 to 24, wherein the signal generating mechanism is accommodated to generate valid and invalid signals to transmit them through a transmitter, the invalid signal is accommodated to establish the memory elements in the objects preventing them, only once the transmission signal has stopped, to respond to any subsequent interrogation signal for a minimum predetermined period of inactivity time, and the valid signal is arranged to reset the memory elements to allow the objects respond to a subsequent question mark.

26. An interrogator according to any of claims 22 to 25, wherein the receiver includes a receiver antenna and a quadrature receiver, the first processor mechanism includes a signal processor for processing baseband components of the identification signal derived from the quadrature receiver in a Manchester reconstructed information signal, and a microprocessor to check errors to decode and check errors in the Manchester signal at least based on the duty cycle, clock speed, information flow duration and calculation of addition check