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RFID and machine intelligence
Is it possible to locate the exact position of an object or a person when literally thousands may be in the vicinity? Is it possible to record the exact movements of the object or person in question and that too automatically? With Radio Frequency Identification (RFID) technology, it is.
RFID is a system that is aimed at increasing efficiency and reducing the workload of data entry operations. The principal areas of application of RFID include: transportation; manufacturing and processing; security, tracking and surveillance; animal tagging; waste management; time and attendance; postal tracking; airline baggage reconciliation; toll management; protection of valuable equipment against theft, unauthorised removal or asset management; controlled access to vehicles, parking areas and fuel facilities; automatic identification of tools in numerically controlled machines; and, identification of product variants and process control in flexible manufacturing systems.
The concept
An RFID system is a wireless system of communications which comprises:
— A transponder or tag consisting of a microchip and a small antenna. The information which is to be processed is written on a microchip. The antenna is used to emit or receive radio signals.
— An interrogator or reader consisting of a transceiver, decoder and antenna. The transceiver is used to receive radio signals which are decoded, to a byte stream by a decoder. The antenna is used to emit/receive radio signals.
The object to be tracked is glued with an RFID tag or transponder. The reader, kept at some position through which objects to be tracked pass, emits radio signals. When the object containing RFID tag comes within the range of radio signals emitted by the reader, the tag is activated and it starts sending the information stored in it in the form of radio signals.
The reader captures the radio signals with its antenna, demodulates it and decodes it to a byte stream with an Analogue Digital Converter (ADC) and sends the information for further processing to the host system connected to it.
Design of readers
Readers can be designed for near-field identification only or they can be programmed to communicate with smart tags and cards that are yards away. A typical reader is shown in the accompanying diagram.
In the figure, to send information the MCU generates adjustable width modulation pulses and sends them to an analogue interface — that is the modulator. Controlled resistances adjust output power and modulation index. To measure actual output voltage, a peak detector at the antenna output is connected to the ADC input of the micro controller.
This serves as a feedback to allow the reader to measure the output power and the modulation index. Because of the tolerance of absolute voltages, the output power measurement using the ADC has to be calibrated by a reference measurement.
The tags
The reader generates a MHz frequency electromagnetic field to transfer power and data to the tags. To form a resonant tank circuit the tag coil on the pads is connected to the analogue interface that includes a capacitor. Together, the capacitor and the coil form a resonance circuit.
The electromagnetic field issued by the reader passes through this coil. Both electromagnetic components, electric and magnetic, could be used by the transponder. The MHz coil voltage is converted to the internal supply voltage by the rectifier and voltage regulator.
The demodulator detects ASK modulation at the coil pads and generates a binary data signal. The modulator performs load modulation at the coil. Data are stored in a memory unit that could be an EEPROM which contains the serial number, configuration data and user data bits.
The EEPROM is divided into blocks, each consisting of specific bytes. A block is the smallest unit that can be read or written. Bit 0 in each byte represents the least significant bit (LSB) and bit 7 the most significant bit (MSB), respectively. Each tag’s unique bits are stored in blocks 0 and 1. Its value is set at factory and is read-only data.
Interrogation
The read/write operations between reader and transponder are performed via the electromagnetic field. The transponder replies to an interrogation request received from the reader, either by returning some data from the transponder, such as an identity code or the value of a measurement, or by returning the original properties of the signal received, with virtually zero time delay, thereby allowing ranging measurements based on time movement.
Now, let’s discuss how a basic communication/interrogation is accomplished:
Each tag or transponder can have four possible states: unselected, selected, halt and quiet. Transition to a new state is launched by a reader command.
1. Each tag begins in an unselected state.
2. To begin the process, each tag independently calculates a time slot position by a pseudo random algorithm.
3. Eventually, the tags will receive specific time slots that are primarily based on their serial numbers but since the number of time slots is finite the reader ignores some tags initially.
4. The unselected read command initiates the transmission of information from the tags. The family code and the application identifier are used to select which tags are to be included in subsequent steps of the interrogation. However, the collision-resolution process continues throughout the selection process.
5. Tags change state to the selected type by an anti-collision/select command. Once a tag is selected, there are three options:
a. read;
b. write block and quit; and,
c. halt and quit.
6. A selected read command requests each tag to send its serial number.
A negotiation governed by complex algorithms follows selection. The process includes the assigning of time slots for each of the selected tags and assigning of the number of blocks to be read from each tag. The reader can also write to the tag. If a write command is issued, a single block is written at a time followed by a quit command.
The point to note here is that products are being interrogated and their answers are being stored and this whole process is automised!
Types of tags
These come in a variety of shapes and sizes:
— Animal tracking tags inserted beneath the skin are as small as a pencil.
— Tags used to track trees or wooden items are screw-shaped.
— Credit card-shaped tags are used for security applications.
An RFID tag can be further categorised as “active” or “passive”. Active tags are powered by internal batteries and the information written on it can be modified. Passive tags operate without external power and obtain power from the radio waves generated by the reader. Passive tags are lighter and less expensive than active ones, their lifetime is virtually unlimited but they have shorter read ranges and require a high-powered reader.
ISO 9000
Introduction of the ISO 9000 standard in production and services sectors implies a radical change in the company quality system. Naturally, competition with similar companies is possible today only with certified ISO quality systems. “Product ID” and “traceability” are procedures in ISO quality systems.
ISO standard requires them to: identify a product from the receipt of material through product delivery; to maintain historical records of the item; to trace assemblies and selected sub-assemblies; to define the methods which must be used to provide product identification and traceability by means of labelling, bar-coding, etc; and to provide procedures for identifying and tracking major components, modules, test results and final product during all stages of production and delivery.
Another procedure in the ISO quality system — namely, “control of non-conforming products” — is used to evaluate defective products and products of questionable integrity, also to evaluate the cause of defects and rework the part, where possible, to create a permanent solution that prevents recurrence of problems.
Creating a material control system in accordance with all these procedures is not easy. But an RFID-based transponder system can create the support to implement all these quality procedures, which are of immense help to the testing, material transport, packaging and incoming quality control departments of a factory with complex final products.
This system has the function to identify all the components of the final product in order to identify and control the suppliers, incoming quality approvals and to trace the material in all production departments.
Material identification system
Such a system comprises three main parts:
1. The data collector host system, for instance, a PC unit;
2. The reader, and;
3. The tag.
The PC contains a database with essential information about all received items, their history, and movements inside the company. In order to update this database, there is a serial communication interface, according to RS 232 standard or a wireless connection, using a radio modem (2.4GHz free licence). Thus, the material control manager can identify and trace all registered material.
Stationary and mobile readers permanently update the database with all changes in material status and their movements. The most important data stored in the database are:
— Identification code (ID) for received materials and sub-assemblies;
— Item description;
— Supplier;
— Incoming data (into incoming warehouse);
— Outgoing data (from finish goods warehouse);
— Actual position in production flow;
— Incoming quality control status, and;
— Item destination (or transport line).
The material control manager can also program the destination for all material. In this way it is possible to optimise internal transportation and material purchasing for all departments.
All data described above are stored both in the memory tag and the database from PC.
The process
In the incoming warehouse, the first step in the identification process is to attach the tag (transponder + antenna) to the material received. Each tag will have a unique identifier number that will be allocated in the database to one received material.
For each transfer from incoming warehouse to production departments, for transfers between production departments, and from production to finish goods warehouses, the stationary readers will record the transfer data to the tag’s memory and will update according to the database from PC.
In the finish goods warehouse, the final product will receive a new tag, with a new unique identification number and specific recorded data in EEPROM.
The final product will be read by a reader to record all these numbers. This reader can read all ID codes for components and sub-assemblies included in the final product.
The material identification system could be used to identify and locate problems in the production flow, making it easier to improve quality. Thus, the system will offer a modern tool for material management and optimisation of material transport in production and on-line production survey.
The writer ikram_e_khuda@hotmail.com has a postgraduate degree in telecommunications
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