WO2006002534A1

WO2006002534A1 - Rfid sensor tag with on-board processing

Info

Publication number: WO2006002534A1
Application number: PCT/CA2005/001032
Authority: WO
Inventors: Michael Petersen; Mykola Sherstyuk
Original assignee: Intelligent Devices Inc.
Priority date: 2004-06-30
Filing date: 2005-06-30
Publication date: 2006-01-12
Also published as: CA2472809A1

Abstract

A tag (10) for attachment to a container or similar package being shipped and/or stored includes a central processing unit (CPU) (12), a timer (14), a crystal resonator (16) connected to the timer, a measuring block (18) connected to the CPU, one or more sensors (26) connected to the measuring block, a communications block (20) connected to the CPU, a feedback block (22) connected to the CPU, and an EEPROM (24) also connected to the CPU. In use a sensor senses environmental changes and the CPU processes signals received from the sensor and stores processed data for later retrieval. When required, the CPU communicates such processed data via the communications block to an RF reader for analysis and use.

Description

RFID SENSOR TAG WITH ON-BOARD PROCESSING

The present invention relates to sensor tags used to monitor environmental conditions with goods in transit or in storage.

BACKGROUND OF THE INVENTION Sensor tags are capable of monitoring environmental conditions associated with goods in transit and/or in storage. Such tags might monitor, for example, the temperature conditions surrounding a shipment of edible produce, such as fruits or vegetables, as they travel from the source thereof to the ultimate vendor of such produce, often in another country. The tag, provided with a suitable temperature sensor, a battery and a suitable electronic chip, can ascertain the actual temperature conditions surrounding the produce at regular intervals and whenever the sensed temperature falls outside a predetermined range (either above or below the range limits). The actual temperature and the time are recorded in the tag's memory. At the end of the trip the memory data can be downloaded for use by whoever has interest in the data. The data can then be analyzed, with the results of the analysis perhaps determining whether the produce is still edible, whether the normal shelf life thereof is still appropriate, or whether changes in shipping procedures need to be made.

Such tags as described above are discussed in commonly owned Canadian Patent Applications Nos. 2,383,049 and 2,387,106 of April 23 and May 21, 2002 respectively. A detriment of such tags is the need to have a sufficiently large memory to accommodate the sensed data, and in particular to accommodate a significant number of excursions outside the specified range. If there are very few excursions then, of course, there are no memory problems; however, if the tag is to be contained in or on the package of produce for a long time, say several weeks, then the problem of memory overload could become significant. If such tags are to be used on a regular basis to improve the overall quality of goods delivered to the eventual consumer then the cost of such tags must not be prohibitive, which means that the most efficient use of the processing capabilities of the tags must be made.

SUMMARY OF THE INVENTION

The present invention overcomes problems associated with existing sensor tags by providing such tags with the capability of processing sensed data on board the tags such that usable data can be downloaded for immediate use and so that the memory requirements for the tags can be minimized. By processing the sensed information on board the tag it is possible to retain only the information that is deemed relevant to the purpose of the tag, i.e. information that relates to sensed conditions that exceed the predetermined threshold values and which are programmed into the tag before it is placed with the goods to be monitored. The minute-by-minute sensed data can be discarded, with only the significant relevant results being retained. Whenever the data is accessed, as for example by a remote reader, an immediate decision can be made as to whether the data indicates a serious issue with the quality of the goods. In the past, as with existing tags, it was necessary to download the raw data as accumulated in the tag's memory, to process that data after downloading, and to then make a decision based on the processed data. With the present invention the off-site processing step is eliminated and pertinent decisions can be made much sooner. For example, when the sensor detects and processes temperature information collected during a shipment of fresh produce from one country to another it would be possible to immediately ascertain whether the shipment should be quarantined because of the shipping experience, perhaps because of extended exposure to excessive temperatures en route.

A sensor in accordance with the present invention can be used to sense more than just temperature. It could be suitably designed to sense one or more of a plurality of environmental conditions encountered during shipping or in storage including, but not limited to, vibration, noise, humidity, radiation and light. It can analyze the output of any type of sensor that can be connected to it. It can also use different (non- silicone/electronic) methods of analyzing temperature or environmental conditions via environment-sensitive specific bioenzymatic or chemical polymer-based and other inks or "blobs" of material which can be used to sense and/or memorize accumulations of events and report back. This could be done passively, so that either the tag itself or the RFID reader system could determine the amount of accumulated effect based on the state-change of such materials. The material itself would be inserted in the antenna circuit, for example, and essentially change the transmissive properties of the tag, thereby indicating the accumulated and/or current environmental exposure to which the specific compound is and/or has been exposed.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described with reference to the attached drawings wherein:

Figure 1 is a schematic block diagram illustrating the major components of a tag in accordance with this invention.

Figure 2A is a schematic representation of the memory block seen in Figure 1. Figure 2B is a typical graph of voltage against time for the measuring block.

Figure 3A is a schematic representation of the communication block seen in Figure 1.

Figure 3B shows graphically typical tag and reader antenna waveforms. Figure 4 is a schematic representation of the feedback block seen in Figure 1.

Figure 5 is a more detailed illustration of the EEPROM block of Figure 1.

Figure 6 is a flow chart showing the basic operation of the tag of the present invention. Figure 7 is a flow chart showing the procedure for tag/reader communications.

Figure 8 shows schematically the form of a message transmitted by the tag.

Figure 9 shows schematically how a "dead" tag can be accessed by a reader.

Figure 10 is an illustration of a commercially available tag in accordance with the present invention. Figure 11 is a "screen shot" of a dialog box in the software which activates the tag of the invention.

Figure 12 is a "screen shot" of the "Overview Tab" in the software showing the tag's information.

Figure 13 is a "screen shot " of the "Histogram Tab" in the software showing the tag's information,

Figure 14 is another "screen shot" of the "Histogram Tab" in the software showing the tag's information.

Figure 15 is a "screen shot" showing the Temperatures and Excursion Trigger Times configuration box of the software. Figure 16 is a "screen shot" of the Histogram configuration box of the software.

Figure 17 is a "screen shot" of the Time Interval configuration box of the software.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference initially to Figure 1 the major components and the connections therebetween are illustrated. Thus, a tag 10 in accordance with this invention includes a programmable CPU 12 connected directly to a clock module or timer 14 controlled by a simple watch crystal resonator 16. Such resonators provide a high degree of stability of resonating frequency under changeable environmental conditions and are suited to reliable mass production. The CPU 12 is connected in parallel to a measuring block 18, a communication block 20, a feedback block 22 and an EEPROM 24. The measuring block 18 is connected to one or more sensors 26 especially adapted to sense the condition or characteristic of interest, such as temperature.

The circuitry for the measuring block is illustrated in Figure 2A, for a plurality of associated sensors. In the illustrated version there are several temperature sensitive sensors provided on the tag, each sensor having a particular temperature range associated therewith. The CPU is set up to measure Rn_sensor at regular, equidistant intervals. While the sensors are disconnected from the CPU the capacitor C_measure is charged to its full capacity (SO = OFF, Sl = ON). After the capacitor has been charged it is disconnected from the power source (SO = OFF, Sl = OFF). When a sensor Rn_sensor is connected to the CPU the capacitor C_meaSure starts to discharge (SO = OFF, Sl = ON). The CPU measures T_measure namely the period during which the capacitor discharges from the logic 1 to logic 0 level. Since T_measure is proportional to a time constant (Rn_sens_or * Cmea_sure) the CPU will calculate the Rn_sensor and accordingly the temperature. The stages of the measuring cycle as outlined above are illustrated in Figure 2B.

Figure 3A illustrates the communication block 20 of the RFID tag 10 of this invention. This is the part of the tag that communicates with the RF Reader used in conjunction with the tag. When a tag enters the RF field a voltage is induced in the tag antenna 28 and through the diode 30 it is detected in the processor. This is the signal to the tag to start sending messages to the reader. This is accomplished by opening and closing the switch S₀ which will change the voltage amplitude on the tag antenna 28. The changes in the voltage amplitude on the tag antenna 28 will affect the voltage at the reader antenna. By monitoring the changes in the reader antenna voltage (due to the tag's modulation data), the data from the tag can be reconstructed at the reader. Figure 3B illustrates representative waveforms as generated by the tag and received at the reader antenna for a typical signal.

Figure 4 illustrates schematically the feedback block 22 which serves the purpose of communicating information from the tag to a user of the tag. The feedback block 22 has a LED diode 32 which will blink in a certain sequence depending on which mode the tag may be in. In place of the LED diode, providing a visual signal to the user, a miniature speaker could be used to provide the user with an audio signal to indicate the tag mode. The nature of the signals imparted to the user will be described hereinbelow in the description of tag operation.

Figure 5 shows a more detailed illustration of the EEPROM block 24 shown in Figure 1.

The basic operation steps associated with the RFID tag of the present invention are set forth in the flow chart of Figure 6, with reference being made as well to the illustration of a commercial tag in Figure 10 and to the "screen shots" of Figures 11 to 17. It is presumed that a customer/user of the tag has obtained a tag from the supplier thereof. The tag on acquisition is not active. It is in a dormant or "sleep" mode. However, the tag was prepared by the supplier to operate in accordance with the customer's specifications, that is it has been programmed to respond to changes in a sensed characteristic relating to the environment in which the tag is to be used, in this case with respect to temperature fluctuations beyond a predetermined range.

A commercial tag 34 is shown in Figure 10. The LED 32 provides the visual indication to a user in regards to the gathered information. A blinking LED indicates to a user that the tag needs to be scanned via an RF Reader due to the excursions of the settings. This feature enables the tag to communicate with the user even if there is no on-site RF Reader present.

To activate a factory-configured tag, a user can place the tag on the RF reader and press the "Temp Record" button in the software to start recording temperature (see Figure 11). Alternatively, to activate a factory -configured tag the user can push the STOP/START button 36 on the tag. The LED light 32 of the feedback block 22 should blink once, indicating that the tag has been turned on. If the user is unsure that he saw the light blink then the pushing step can be repeated. Once the light has blinked once the tag is in its "packaging" mode, which means that it is activated but it will not record any events for a predetermined period of time. For example, there could be a delay of about 16 minutes during which time the user can place the tag in a package or shipment of material. After the predetermined period of time has expired the tag will start processing signals received from the sensor associated therewith and recording any excursions from the set range as programmed into the tag.

Once the shipment has reached its destination the user will push the START/STOP button 36 to stop the tag. The LED light 32 should blink twice indicating a "stop" condition. The pushing step can be repeated if the user is unsure whether the light blinked twice. If the temperatures sensed during the shipment crossed the excursion limit as programmed initially into the tag, such that the acceptable temperature range was exceeded, the LED light 32 will blink for a predetermined period of time, say 16 minutes, so that the user can download the relevant data. If there were no excursions during the shipment the LED light will not blink.

Three modes in the software can be used to view the information collected by the tag. The "Overview" Tab in the software shows the Last Recorded Temperature (LRT) and Mean Kinetic Temperature (MKT) recorded by the tag during its period of activation. It shows the Minimum and Maximum temperatures and the Logging Duration Logging Duration of the Tag while activated. "Status: Check" is an advisory that indicates the tag has captured temperature excursions. "Status: OK" indicates that the tag has not captured any temperature excursions. Figure 12 displays a screenshot of the "Overview" Tab in the software.

The "Histogram" Tab, see Figure 13, in the software displays a bar chart showing the number of times a specific temperature was recorded by the tag during its activation period. Two vertical black lines, displayed in the Histogram, represent the upper and lower temperature thresholds configured for the tag. The left-most black line shows the low temperature threshold, while the right-most black line shows the high temperature threshold. Green bars (grey in Figure 13) identify the recorded temperatures that were within the tag's configured upper and lower temperature thresholds. Red bars (dark grey in Figure 13) identify the temperatures that exceeded the tag's configured high temperature threshold.

The "Time/Temp" Tab (see Figure 14) is another mode to view the data collected by the tag during its activation period. It displays the low temperature threshold and high temperature threshold set by the user. The desired temperature range, displayed as a white region, is shown within these thresholds. The grey regions, above and below the white region represent the temperature ranges that are outside the desired temperature range.

A user can configure the minimum and maximum threshold temperatures of the tag through the software. A user can also configure the "Excursion Trigger Time" (in minutes), which is the length of time after which an excursion is identified. Figure 15 displays the configuration box of the temperatures and Excursion Trigger Times.

A Histogram consists of temperature ranges that are known as bins. An activated tag records the duration of time it was exposed to each of these bins. The tag records the temperature more frequently within these bins; hence the accuracy of the bins is greater than the temperatures recorded outside these bins. A tag can be configured to establish desired bins for the histogram. Figure 16 shows the configuration box used to customize the histogram. A user can configure the length of time between temperature recordings stored by the tag. The "Soaking Interval", which can also be configured, is the time interval between activating the tag, and the first temperature recording stored by the tag. Figure 17 displays the time interval configuration box in the software.

Figure 7 illustrates a flow chart which details the steps when the tag interfaces with a reader. When the tag has been turned off as indicated above it enters a standby mode, awaiting a signal from the reader. If the signal received from the reader is in a proper sequence the tag will enter its Receiving mode, execute the command imparted to it by the reader and thereafter return to its Sleep or Sensor measuring mode. If the signal is not in the proper sequence the tag immediately enters its Sleep/Sensor measuring mode. When the signal is in the proper sequence the reader can receive processed data from the tag and it, in turn, can provide the tag with new program instructions if necessary.

The format of a message transmitted from the tag to the reader will be as shown in Figure 8. There it is seen that the message will have seven components, A through G. Component A identifies the version of the tag and component B identifies the protocol version for that tag. Component C identifies the number of data packets that will be transmitted. Component D is the actual packet number being transmitted and component E will be the data associated with that packet number.

In the event that the tag battery dies during the shipment it is still possible to obtain data from the tag. Figure 9 shows schematically how this is achieved. The required energy can be extracted from the LF field provided by the reader. The voltage induced on the 13.56 MHz antenna will be transmitted to the CPU so that the data can be transmitted to the reader.

The tag of the present invention never generates RF energy itself, so it is 100% safe to be housed within a shipping container, no matter what the contents might be. It is even safe for use with explosives that require monitoring during shipment when temperature or humidity might be a concern with respect to the effectiveness thereof. The tag still can be scanned remotely by a reader, even through the wall of the container if necessary. The tag of this invention operates by storing and presenting data in the form of temperature histograms, with variable temperature resolution. Each histogram can have up to 28 bins, for example there could be temperature bins for +1°C, +2°C, +3°C, +4°C, +5°C, +6°C and +7°C if those represent the temperatures of most concern with respect to a predetermined temperature limit. When in the monitoring mode the chip will know for how long the device was exposed to each of those temperatures. The rest of the temperature range would be covered by temperature bins with much less resolution, for example -10°C to -5°C, -5°C to 0⁰C, +20⁰C to +35°C, etc. The tag will be able to determine for how long it was exposed to temperatures within each of these ranges. Whenever the temperature crosses any of the upper or lower limits of a range there will be a time stamp created, defining an excursion point.

The present invention utilizes a unique method for keeping track of time, in comparison to traditional methods. A traditional method of keeping track of real time events is to: a) provide a device which increments the local time count value N_jocaι every Tincrjocai units of time; b) synchronize the timing device with a reference timing device, say at a particular moment with a value of T_sync units of reference time. The local time count N=O at this moment. The reference time T_sync = T_lncr_ref * N_ref. c) keep track of N_ι_OCai values for each event about which a recorded time is required; and d) calculate the event time at each moment as:

■ event ⁼ " sync + ■ iπcr_local "_local_(event)

There are several problems associated with such a method; in particular T_{incr l}oc_al must be stable under different environmental conditions and the value of Ti_ncrjocai must be as close as possible to the value of T,_{ncr re}f. It is very difficult to achieve these requirements with mass production. Electronic time keeping devices usually use crystal resonators which give a high stability of resonating frequency under changeable environmental conditions. This is a solution to the first problem. However, it is very complicated to ensure that T_incrj_Ocai = Tm_Cr__ref- The process involves high precision production techniques for manufacture of the crystals, as well as calibration of each individual resonator.

With the present invention accurate time keeping is simplified and improved. The present device increments the local time count value T_ι_ocal every Tj_nCr_i_ocai units of time.

At the moment of initial synchronization values of T_synci and NJ_0C3I1 are recorded. At the moment of final synchronization values of T_sync2 and N_ι_0Cai₂ are recorded. Then, T_event

⁼ (T_Sync2 " Tsynci) /(N_|_Ocai2 -N_|_ocau) * Nj_oca|_event-

As with the traditional method T_incrj_Ocai must be stable; however, it could be much different from T_incr__ref, which means in turn that it is not necessary to use expensive, highly accurate crystals. On the other hand, it is necessary to have accurate values of T_synci and T_synC2 , which means that the synchronization device, the reader, must have be calibrated for time or have access to an atomic clock (as for example through the internet). Mass produced tags in accordance with the present invention will be of lower cost in comparison to tags which provide time keeping in accordance with traditional methods, since it is only necessary to have the synchronizing devices accurate. In this case the reader will provide the required accurate timing, it being noted that the reader will be a low volume production device in comparison to the tag, which will be a high volume production device. The software is programmed to calculate the Mean Kinetic Temperature (MKT), a calculated, fixed temperature that simulates the effects of the temperature variations over duration of time. It expresses the cumulative thermal stress experienced by a tag at varying temperatures during its activation period.

Equations 1, 2, and 3 are the formulas used by the software to calculate MKT. The software retrieves the middle temperature (T_BιnMιd) of each bin and the duration of time the tag spent in that temperature (BinCountn). Then, it calculates the total amount of time spent in all the temperatures recorded (Total Samples). ΔH is the activation energy constant and R is the universal gas constant.

AH • R Tk(k) s Tk(k),_mc ≡ ^: Equation 1

^{# binS} , . „ f- ΔH / (R • TBmMKi)I

∑ binCountn * e^{v ;}

X = In i = l Equation 2

Total Samples Tk(k)imc -> Tk(k) as Binwidth — » 0 and #Bins — > ∞ Equation 3

In summary of the foregoing the present invention provides an inexpensive tag that can be included in any type of shipping container, with any type of product, and which will monitor temperature excursions with respect to predetermined limits or ranges. The tag processes data on board, using a unique time keeping process and requires very little memory to retain the processed data. The data can be downloaded using RFID technology to a reader should there be any excursions during shipment or storage. The tag uses a simple visual indicator to alert the user to any excursions once the tag has been turned off at its destination. The temperature sensor is of the digital type and can measure temperature in 1°C increments. It will have an accuracy of ±1°C from -20⁰C to +30⁰C. It can support one additional sensor, to sense for example humidity or vibration. It utilizes a programmable status LED warning light. It records a long-term temperature histogram, with each histogram having up to 28 bins. Each such bin can store up to 65,536 time points and it can record up to 10 excursions when the sensed temperature leaves the specified range. It provides for real-time, on-board data analysis. It communicates with its host (the reader) using proprietary RF communication protocol. It has a unique 32-bit ID number, assuring absolute traceability because no two tags will be alike. It provides a 1 minute time resolution of recorded events and it provides an accuracy of timing reported of ±5 minutes if the data is scanned within 60 days. The battery operating voltage is 2.5V to 3.5V and the maximum storage time in the non-active mode is 12 months. The maximum operating time in the active mode is 6 months. The operating temperature ranges are -30⁰C to +60⁰C in the non-active mode and -20⁰C to +30⁰C in the active mode. Data can be retrieved for a period of up to 7 years. The RF reader range is 5cm or greater and two tags could be read at the same time without any fear of the transmitted data being compromised. The tag's internal clock is accurate to ±2 minutes/month. The tag is capable of processing and storing the data in protected logic file format (.Idf). The semi-flexible shape of the tag is resistant to temperature, humidity, vibration and shock.

The foregoing has described a unique tag that can be used on any type of container, pallet, bag, package, etc. to monitor and report on environmental changes experienced by the package during shipment and/or storage, providing useful information in a reliable, inexpensive manner to a user. The significant features of the tag have been described, but it is understood that alterations and/or additions to those features could be accomplished by a skilled person without departing from the spirit of the invention.

Claims

s 1. A tag for attachment to a container or similar package being shipped and/or stored, said tag comprising : a central processing unit (CPU); a timer; a crystal resonator connected to said timer; a measuring block connected to said CPU; sensing means connected to said measuring block; a communications block connected to said CPU; a feedback block connected to said CPU; and an EEPROM connected to said CPU; whereby in use said sensing means senses environmental changes to which said package is exposed during shipment and/or storage; said CPU processes signals received from said sensing means and stores processed data for later retrieval; and when required said CPU communicates such processed data via said communications block to a party interested in such processed data.

2. A tag according to claim 1 wherein said feedback block includes an LED for communicating status information to a user.

3. A tag according to claim 1 or claim 2 wherein said sensing means includes a plurality of individual temperature sensors, each sensor having a particular temperature range associated therewith.

4. A tag according to any one of claims 1 to 3 wherein said communications block includes an antenna in which a voltage is induced by an RF field associated with an RF reader to signal the tag to transmit data to the reader through the antenna.

5. A tag according to claim 4 in which changes in the voltage amplitude on the antenna will affect the voltage at an antenna of said reader, and by monitoring the changes at the reader antenna, data transmitted from the tag can be reconstructed at the reader.

6. A tag according to any one of claims 1 to 5 wherein said tag is capable of storing and presenting data in the form of temperature histograms, with each histogram having up to 28 bins representing temperature ranges of interest, said tag being capable of determining the length of time that the tag was exposed to temperatures within each such range.

7. A system for monitoring environmental conditions respecting a container or similar package being shipped and/or stored, said system comprising at least one tag to be included with said container or package, and at least one reader for receiving information processed by said at least one tag, wherein said tag comprises: a central processing unit (CPU); a timer; a crystal resonator connected to said timer; a measuring block connected to said CPU; sensing means connected to said measuring block; a communications block connected to said CPU; a feedback block connected to said CPU; and an EEPROM connected to said CPU; and wherein said reader comprises: computer means for activating and processing information received from said at least one tag, and antenna means for communicating with said tag; whereby in use said sensing means senses environmental changes to which said package is exposed during shipment and/or storage; said CPU processes signals received from said sensing means and stores processed data for later retrieval; and when required said CPU communicates such processed data via said communications block to said reader by way of said antenna.

8. A method of keeping tack of time in a tag according to claim 1 including the steps of:

- establishing and recording initial synchronization values of T_synci and N_ι_0Caii where T_synci is an initial synchronization temperature and N_Jocau is an initial local time count value;

- establishing and recording final synchronization values of T_sync₂ and IMj_0Cai₂ where T_syn.₂ is a final synchronization temperature and N_Jocaι₂ is a final local time count value; and - incrementing the local time count value T_Jocaι every T_ιncrj_Ocai units of time; whereby:

Tevent ⁼ (T_Sync2 " T_synci)/(Nj_oca|2 " Nj_ocan) * Nj_oca|__event-