RFID tag chips and tags refraining from participating in a subsequent inventorying attempt and methods

RFID tags and chips for RFID tags are capable of being inventoried in one or more early attempts. These tags are capable of then refraining from participating in one or more subsequent inventorying attempts. In some embodiments refraining is performed solely by the tag, while in others it is guided by the RFID reader. In some embodiments, an inventoried indicator in the tag becomes updated upon backscattering. The updated value is used by the tag to recognize a subsequent attempt, and thus refrain from participating in it. This permits the subsequent attempt to be used more intensively for inventorying the more elusive, harder-to-read tags, especially in more demanding scenarios.

FIELD OF THE INVENTION

The present description addresses the field of Radio Frequency IDentification (RFID) systems.

BACKGROUND

Radio Frequency IDentification (RFID) systems typically include RFID tags and RFID readers. RFID readers are also known as RFID reader/writers or RFID interrogators. RFID systems can be used in many ways for locating and identifying objects to which the tags are attached. RFID systems are particularly useful in product-related and service-related industries for tracking objects being processed, inventoried, or handled. In such cases, an RFID tag is usually attached to an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to interrogate one or more RFID tags. The reader transmitting a Radio Frequency (RF) wave performs the interrogation. The RF wave is typically electromagnetic, at least in the far field. The RF wave can also be predominantly electric or magnetic in the near field.

A tag that senses the interrogating RF wave responds by transmitting back another RF wave. The tag generates the transmitted back RF wave either originally, or by reflecting back a portion of the interrogating RF wave in a process known as backscatter. Backscatter may take place in a number of ways.

The reflected-back RF wave may further encode data stored internally in the tag, such as a number. The response is demodulated and decoded by the reader, which thereby identifies, counts, or otherwise interacts with the associated item. The decoded data can denote a serial number, a price, a date, a destination, other attribute(s), any combination of attributes, and so on.

An RFID tag typically includes an antenna system, a radio section, a power management section, and frequently a logical section, a memory, or both. In earlier RFID tags, the power management section included an energy storage device, such as a battery. RFID tags with an energy storage device are known as active or semi-active tags. Advances in semiconductor technology have miniaturized the electronics so much that an RFID tag can be powered solely by the RF signal it receives. Such RFID tags do not include an energy storage device, and are called passive tags.

Problems arise when more and more tags are desired to be inventoried, in less and less time. There is less time as tags are moving.

An emerging pattern is that some tags are occasionally harder to read than others, even with repeated inventorying attempts. Such tags could be, for example, in the center of a large group. This pattern can become a problem when there is less time to read the group, such as when the group is moving past the antennas without stopping.

BRIEF SUMMARY

The invention improves over the prior art.

Briefly, the present invention provides RFID tags and chips for RFID tags that are capable of being inventoried in one or more early attempts. These tags are capable of then refraining from participating in one or more subsequent inventorying attempts. In some embodiments refraining is performed solely by the tag, while in others it is guided by the RFID reader.

The invention offers the advantage that, when these tags refrain from participating in the subsequent attempts, they permit these attempts to be used more intensively for inventorying the more elusive, harder-to-read tags, especially in more demanding scenarios.

These and other features and advantages of the invention will be better understood from the specification of the invention, which includes the following Detailed Description and accompanying Drawings.

DETAILED DESCRIPTION

The present invention is now described. While it is disclosed in its preferred form, the specific embodiments of the invention as disclosed herein and illustrated in the drawings are not to be considered in a limiting sense. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Indeed, it should be readily apparent in view of the present description that the invention may be modified in numerous ways. Among other things, the present invention may be embodied as devices, methods, software, and so on. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, an entirely firmware embodiment, or an embodiment combining aspects of the above. This description is, therefore, not to be taken in a limiting sense.

FIG. 1is a diagram of components of a typical RFID system100, incorporating aspects of the invention. An RFID reader110transmits an interrogating Radio Frequency (RF) wave112. RFID tag120in the vicinity of RFID reader110may sense interrogating RF wave112, and generate wave126in response. RFID reader110senses and interprets wave126.

Reader110and tag120exchange data via wave112and wave126. In a session of such an exchange, each encodes, modulates, and transmits data to the other, and each receives, demodulates, and decodes data from the other. The data is modulated onto, and demodulated from, RF waveforms.

Encoding the data in waveforms can be performed in a number of different ways. For example, protocols are devised to communicate in terms of symbols, also called RFID symbols. A symbol for communicating can be a delimiter, a calibration symbol, and so on. Further symbols can be implemented for ultimately exchanging binary data, such as “0” and “1”, if that is desired. In turn, when the waveforms are processed internally by reader110and tag120, they can be equivalently considered and treated as numbers having corresponding values, and so on.

Tag120can be a passive tag or an active or semi-active tag, i.e. having its own power source. Where tag120is a passive tag, it is powered from wave112.

FIG. 2is a diagram of an RFID tag220, which can be the same as tag120ofFIG. 1. Tag220is implemented as a passive tag, meaning it does not have its own power source. Much of what is described in this document, however, applies also to active tags.

Tag220is formed on a substantially planar inlay222, which can be made in many ways known in the art. Tag220includes an electrical circuit, which is preferably implemented in an integrated circuit (IC)224. IC224is arranged on inlay222.

Tag220also includes an antenna for exchanging wireless signals with its environment. The antenna is usually flat and attached to inlay222. IC224is electrically coupled to the antenna via suitable antenna ports (not shown inFIG. 2).

The antenna may be made in a number of ways, as is well known in the art. In the example ofFIG. 2, the antenna is made from two distinct antenna segments227, which are shown here forming a dipole. Many other embodiments are possible, using any number of antenna segments.

In some embodiments, an antenna can be made with even a single segment. Different points of the segment can be coupled to one or more of the antenna ports of IC224. For example, the antenna can form a single loop, with its ends coupled to the ports. It should be remembered that, when the single segment has more complex shapes, even a single segment could behave like multiple segments, at the frequencies of RFID wireless communication.

In operation, a signal is received by the antenna, and communicated to IC224. IC224both harvests power, and responds if appropriate, based on the incoming signal and its internal state. In order to respond by replying, IC224modulates the reflectance of the antenna, which generates the backscatter from a wave transmitted by the reader. Coupling together and uncoupling the antenna ports of IC224can modulate the reflectance, as can a variety of other means.

In the embodiment ofFIG. 2, antenna segments227are separate from IC224. In other embodiments, antenna segments may alternately be formed on IC224, and so on.

The components of the RFID system ofFIG. 1may communicate with each other in any number of modes. One such mode is called full duplex. Another such mode is called half-duplex, and is described below.

FIG. 3is a conceptual diagram300for explaining the half-duplex mode of communication between the components of the RFID system ofFIG. 1, especially when tag120is implemented as passive tag220ofFIG. 2. The explanation is made with reference to a TIME axis, and also to a human metaphor of “talking” and “listening”. The actual technical implementations for “talking” and “listening” are now described.

RFID reader110and RFID tag120talk and listen to each other by taking turns. As seen on axis TIME, when reader10talks to tag120the communication session is designated as “R→T”, and when tag120talks to reader110the communication session is designated as “T→R”. Along the TIME axis, a sample R→T communication session occurs during a time interval312, and a following sample T→R communication session occurs during a time interval326. Of course interval312is typically of a different duration than interval326here the durations are shown approximately equal only for purposes of illustration.

In terms of actual technical behavior, during interval312, reader110talks to tag120as follows. According to block352, reader110transmits wave112, which was first described inFIG. 1. At the same time, according to block362, tag120receives wave112and processes it, to extract data and so on. Meanwhile, according to block372, tag120does not backscatter with its antenna, and according to block382, reader110has no wave to receive from tag120.

During interval326, tag120talks to reader110as follows. According to block356, reader110transmits a Continuous Wave (CW), which can be thought of as a carrier signal that ideally encodes no information. As discussed before, this carrier signal serves both to be harvested by tag120for its own internal power needs, and also as a wave that tag120can backscatter. Indeed, during interval326, according to block366, tag120does not receive a signal for processing. Instead, according to block376, tag120modulates the CW emitted according to block356, so as to generate backscatter wave126. Concurrently, according to block386, reader110receives backscatter wave126and processes it.

In the above, an RFID reader/interrogator may communicate with one or more RFID tags in any number of ways. Some such ways are called protocols. A protocol is a specification that calls for specific manners of signaling between the reader and the tags.

One such protocol is called the Specification for RFID Air Interface-EPC™ Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz 960 MHz, which is also colloquially known as “the Gen2 Spec”. The Gen2 Spec has been ratified by EPCglobal, which is an organization that maintains a website at: <http://www.epcglobalinc.org/> at the time this document is initially filed with the USPTO. Version 1.1.0 of the Gen2 Spec is hereby incorporated by reference in its entirety.

In addition, a protocol can be a variant of a stated specification such as the Gen2 Spec, for example including fewer or additional commands than the stated specification calls for, and so on. In such instances, additional commands are sometimes called custom commands.

FIG. 4is a block diagram of an electrical circuit424. Circuit424may be formed in an IC of an RFID tag, such as IC224ofFIG. 2. Circuit424has a number of main components that are described in this document. Circuit424may have a number of additional components from what is shown and described, or different components, depending on the exact implementation.

Circuit424includes at least two antenna connections432,433, which are suitable for coupling to one or more antenna segments (not shown inFIG. 4). Antenna connections432,433may be made in any suitable way, such as using pads and so on. In a number of embodiments more than two antenna connections are used, especially in embodiments where more antenna segments are used.

Circuit424includes a section435. Section435may be implemented as shown, for example as a group of nodes for proper routing of signals. In some embodiments, section435may be implemented otherwise, for example to include a receive/transmit switch that can route a signal, and so on.

Circuit424also includes a Power Management Unit (PMU)441. PMU441may be implemented in any way known in the art, for harvesting raw RF power received via antenna connections432,433. In some embodiments, PMU441includes at least one rectifier, and so on.

In operation, an RF wave received via antenna connections432,433is received by PMU441, which in turn generates power for components of circuit424. This is true for either or both R→T and T→R sessions, whether or not the received RF wave is modulated.

Circuit424additionally includes a demodulator442. Demodulator442demodulates an RF signal received via antenna connections432,433. Demodulator442may be implemented in any way known in the art, for example including an attenuator stage, an amplifier stage, and so on.

Circuit424further includes a processing block444. Processing block444receives the demodulated signal from demodulator442, and may perform operations. In addition, it may generate an output signal for transmission.

Processing block444may be implemented in any way known in the art. For example, processing block444may include a number of components, such as a processor, memory, a decoder, an encoder, and so on.

Circuit424additionally includes a modulator446. Modulator446modulates an output signal generated by processing block444. The modulated signal is transmitted by driving antenna connections432,433, and therefore driving the load presented by the coupled antenna segment or segments. Modulator446may be implemented in any way known in the art, for example including a driver stage, amplifier stage, and so on.

In one embodiment, demodulator442and modulator446may be combined in a single transceiver circuit. In another embodiment, modulator446may include a backscatter transmitter or an active transmitter. In yet other embodiments, demodulator442and modulator446are part of processing block444.

Circuit424additionally includes a memory450, which stores data452. Memory450is preferably implemented as a Nonvolatile Memory (NVM), which means that data452is retained even when circuit424does not have power, as is frequently the case for a passive RFID tag.

It will be recognized at this juncture that the shown components of circuit424can be those of a circuit of an RFID reader according to the invention, with or without needing PMU441. Indeed, an RFID reader can be powered differently, such as from a wall outlet, a battery, and so on. Additionally, when circuit424is configured as a reader, processing block444may have additional Inputs/Outputs (I/O) to a terminal, network, or other such devices or connections.

In terms of processing a signal, circuit424operates differently during a R→T session and a T→R session. The different operations are described below, in this case with circuit424representing an RFID tag.

FIG. 5Ashows version524-A of components of circuit424ofFIG. 4, further modified to emphasize a signal operation during a R→T session (receive mode of operation) during time interval312ofFIG. 3. An RF wave is received from antenna connections432,433, and then a signal is demodulated from demodulator442, and then input to processing block444as C_IN. In one embodiment according to the present invention, C_IN may include a received stream of symbols.

Version524-A shows as relatively obscured those components that do not play a part in processing a signal during a R→T session. Indeed, PMU441may be active, but only in converting raw RF power. And modulator446generally does not transmit during a R→T session. Modulator446typically does not interact with the received RF wave significantly, either because switching action in section435ofFIG. 4decouples the modulator446from the RF wave, or by designing modulator446to have a suitable impedance, and so on.

While modulator446is typically inactive during a R→T session, it need not be always the case. For example, during a R→T session, modulator446could be active in other ways. For example, it could be adjusting its own parameters for operation in a future session.

FIG. 5Bshows version524-B of components of circuit424ofFIG. 4, further modified to emphasize a signal operation during a T→R session during time interval326ofFIG. 3. A signal is output from processing block444as C_OUT. In one embodiment according to the present invention, C_OUT may include a transmission stream of symbols. C_OUT is then modulated by modulator446, and output as an RF wave via antenna connections432,433.

Version524-B shows as relatively obscured those components that do not play a part in processing a signal during a T→R session. Indeed, PMU441may be active, but only in converting raw RF power. And demodulator442generally does not receive during a T→R session. Demodulator442typically does not interact with the transmitted RF wave, either because switching action in section435decouples the demodulator442from the RF wave, or by designing demodulator442to have a suitable impedance, and so on.

While demodulator442is typically inactive during a T→R session, it need not be always the case. For example, during a T→R session, demodulator442could be active in other ways. For example, it could be adjusting its own parameters for operation in a future session.

FIG. 6is a block diagram showing a detail of an RFID reader system610, which can be the same as reader110shown inFIG. 1. A unit620is also known as a box620, and has at least one antenna driver630. In some embodiments it has four drivers630. For each driver630there is an output device for a connector. The output device is typically a coaxial cable plug. Accordingly connectors635can be attached to the output devices of the provided respective drivers630, and then connectors635can be attached to respective antennas640.

A driver630can send to its respective antenna640a driving signal that is in the RF range, which is why connector635is typically but not necessarily a coaxial cable. The driving signal causes the antenna640to transmit an RF wave612, which is analogous to RF wave112ofFIG. 1. In addition, RF wave626can be backscattered from the RFID tags, analogous to RF wave126ofFIG. 1. Backscattered RF wave626then ultimately becomes a signal sensed by unit620.

Unit620also has other components650, such as hardware and/or software and/or firmware, which may be described in more detail later in this document. Components650control drivers630, and as such cause RF wave612to be transmitted, and the sensed backscattered RF wave626to be interpreted. Optionally and preferably there is a communication link625to other equipment, such as computers and the like, for remote operation of system610.

FIG. 7is a block diagram of a whole RFID reader system700according to embodiments. System700includes a local block710, and optionally remote components770. Local block710and remote components770can be implemented in any number of ways. It will be recognized that reader110ofFIG. 1is the same as local block710, if remote components770are not provided. Alternately, reader110can be implemented instead by system700, of which only the local block710is shown inFIG. 1. Plus, local block710can be unit620ofFIG. 6.

Local block710is responsible for communicating with the tags. Local block710includes a block751of an antenna and a driver of the antenna for communicating with the tags. Some readers, like that shown in local block710, contain a single antenna and driver. Some readers contain multiple antennas and drivers and a method to switch signals among them, including sometimes using different antennas for transmitting and for receiving. And some readers contain multiple antennas and drivers that can operate simultaneously. A demodulator/decoder block753demodulates and decodes backscattered waves received from the tags via antenna block751. Modulator/encoder block754encodes and modulates an RF wave that is to be transmitted to the tags via antenna block751.

Local block710additionally includes an optional local processor756. Processor756may be implemented in any number of ways known in the art. Such ways include, by way of examples and not of limitation, digital and/or analog processors such as microprocessors and digital-signal processors (DSPs); controllers such as microcontrollers; software running in a machine such as a general purpose computer; programmable circuits such as Field Programmable Gate Arrays (FPGAs), Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices (PLDs), Application Specific Integrated Circuits (ASIC), any combination of one or more of these; and so on. In some cases some or all of the decoding function in block753, the encoding function in block754, or both, may be performed instead by processor756.

Local block710additionally includes an optional local memory757. Memory757may be implemented in any number of ways known in the art. Such ways include, by way of examples and not of limitation, nonvolatile memories (NVM), read-only memories (ROM), random access memories (RAM), any combination of one or more of these, and so on. Memory757, if provided, can include programs for processor756to run, if provided.

In some embodiments, memory757stores data read from tags, or data to be written to tags, such as Electronic Product Codes (EPCs), Tag Identifiers (TIDs) and other data. Memory757can also include reference data that is to be compared to the EPC codes, instructions and/or rules for how to encode commands for the tags, modes for controlling antenna751, and so on. In some of these embodiments, local memory757is provided as a database.

Some components of local block710typically treat the data as analog, such as the antenna/driver block751. Other components such as memory757typically treat the data as digital. At some point there is a conversion between analog and digital. Based on where this conversion occurs, a whole reader may be characterized as “analog” or “digital”, but most readers contain a mix of analog and digital functionality.

If remote components770are indeed provided, they are coupled to local block710via an electronic communications network780. Network780can be a Local Area Network (LAN), a Metropolitan Area Network (MAN), a Wide Area Network (WAN), a network of networks such as the internet, or a mere local communication link, such as a USB, PCI, and so on. In turn, local block710then includes a local network connection759for communicating with network780.

There can be one or more remote component(s)770. If more than one, they can be located at the same location, or in different locations. They can access each other and local block710via network780, or via other similar networks, and so on. Accordingly, remote component(s)770can use respective remote network connections. Only one such remote network connection779is shown, which is similar to local network connection759, etc.

Remote component(s)770can also include a remote processor776. Processor776can be made in any way known in the art, such as was described with reference to local processor756.

Remote component(s)770can also include a remote memory777. Memory777can be made in any way known in the art, such as was described with reference to local memory757. Memory777may include a local database, and a different database of a Standards Organization, such as one that can reference EPCs.

Of the above-described elements, it is advantageous to consider a combination of these components, designated as operational processing block790. Block790includes those that are provided of the following: local processor756, remote processor776, local network connection759, remote network connection779, and by extension an applicable portion of network780that links connection759with connection779. The portion can be dynamically changeable, etc. In addition, block790can receive and decode RF waves received via antenna751, and cause antenna751to transmit RF waves according to what it has processed.

Block790includes either local processor756, or remote processor776, or both. If both are provided, remote processor776can be made such that it operates in a way complementary with that of local processor756. In fact, the two can cooperate. It will be appreciated that block790, as defined this way, is in communication with both local memory757and remote memory777, if both are present.

Accordingly, block790is location agnostic, in that its functions can be implemented either by local processor756, or by remote processor776, or by a combination of both. Some of these functions are preferably implemented by local processor756, and some by remote processor776. Block790accesses local memory757, or remote memory777, or both for storing and/or retrieving data.

Reader system700operates by block790generating communications for RFID tags. These communications are ultimately transmitted by antenna block751, with modulator/encoder block754encoding and modulating the information on an RF wave. Then data is received from the tags via antenna block751, demodulated and decoded by demodulator/decoder block753, and processed by processing block790.

The invention also includes methods. Some are methods of operation of an RFID reader or RFID reader system. Others are methods for controlling an RFID reader or RFID reader system.

Another optional way is for one or more of the individual operations of the methods to be performed in conjunction with one or more human operators performing some of them. These human operators need not be collocated with each other, but each can be only with a machine that performs a portion of the program.

The invention additionally includes programs, and methods of operation of the programs. A program is generally defined as a group of steps or operations leading to a desired result, due to the nature of the elements in the steps and their sequence. A program is usually advantageously implemented as a sequence of steps or operations for a processor, such as the structures described above.

Performing the steps, instructions, or operations of a program requires manipulation of physical quantities. Usually, though not necessarily, these quantities may be transferred, combined, compared, and otherwise manipulated or processed according to the steps or instructions, and they may also be stored in a computer-readable medium. These quantities include, for example, electrical, magnetic, and electromagnetic charges or particles, states of matter, and in the more general case can include the states of any physical devices or elements. It is convenient at times, principally for reasons of common usage, to refer to information represented by the states of these quantities as bits, data bits, samples, values, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are associated with the appropriate physical quantities, and that these terms are merely convenient labels applied to these physical quantities, individually or in groups.

The invention furthermore includes storage media. Such media, individually or in combination with others, have stored thereon instructions of a program made according to the invention. A storage medium according to the invention is a computer-readable medium, such as a memory, and is read by a processor of the type mentioned above. If a memory, it can be implemented in a number of ways, such as Read Only Memory (ROM), Random Access Memory (RAM), etc., some of which are volatile and some non-volatile.

Even though it is said that the program may be stored in a computer-readable medium, it should be clear to a person skilled in the art that it need not be a single memory, or even a single machine. Various portions, modules or features of it may reside in separate memories, or even separate machines. The separate machines may be connected directly, or through a network such as a local access network (LAN) or a global network such as the Internet.

Often, for the sake of convenience only, it is desirable to implement and describe a program as software. The software can be unitary, or thought in terms of various interconnected distinct software modules.

This detailed description is presented largely in terms of flowcharts, algorithms, and symbolic representations of operations on data bits on and/or within at least one medium that allows computational operations, such as a computer with memory. Indeed, such descriptions and representations are the type of convenient labels used by those skilled in programming and/or the data processing arts to effectively convey the substance of their work to others skilled in the art. A person skilled in the art of programming may use these descriptions to readily generate specific instructions for implementing a program according to the present invention.

Embodiments of an RFID reader system can be implemented as hardware, software, firmware, or any combination. It is advantageous to consider such a system as subdivided into components or modules. A person skilled in the art will recognize that some of these components or modules can be implemented as hardware, some as software, some as firmware, and some as a combination. An example of such a subdivision is now described.

FIG. 8is a block diagram illustrating an overall architecture of an RFID reader system800according to embodiments. It will be appreciated that system800is considered subdivided into modules or components. Each of these modules may be implemented by itself, or in combination with others. It will be recognized that some aspects are parallel with those ofFIG. 7. In addition, some of them may be present more than once.

RFID reader system800includes one or more antennas810, and an RF Front End820, for interfacing with antenna(s)810. These can be made as described above. In addition, Front End820typically includes analog components.

System800also includes a Signal Processing module830. In this embodiment, module830exchanges waveforms with Front End820, such as I and Q waveform pairs. In some embodiments, signal processing module830is implemented by itself in an FPGA.

System800also includes a Physical Driver module840, which is also known as Data Link. In this embodiment, module840exchanges bits with module830. Data Link840can be the stage associated with framing of data. In one embodiment, module840is implemented by a Digital Signal Processor.

System800additionally includes a Media Access Control module850, which is also known as MAC layer. In this embodiment, module850exchanges packets of bits with module840. MAC layer850can be the stage for making decisions for sharing the medium of wireless communication, which in this case is the air interface. Sharing can be between reader system800and tags, or between system800with another reader, or between tags, or a combination. In one embodiment, module850is implemented by a Digital Signal Processor.

System800moreover includes an Application Programming Interface module860, which is also known as API, Modem API, and MAPI. In some embodiments, module860is itself an interface for a user.

All of these functionalities can be supported by one or more processors. One of these processors can be considered a host processor. Such a processor would, for example, exchange signals with MAC layer850via module860. In some embodiments, the processor can include applications for system800. In some embodiments, the processor is not considered as a separate module, but one that includes some of the above-mentioned modules of system800.

A user interface880may be coupled to API860. User interface880can be manual, automatic, or both. It can be supported by a separate processor than the above mentioned processor, or implemented on it.

It will be observed that the modules of system800form something of a chain. Adjacent modules in the chain can be coupled by the appropriate instrumentalities for exchanging signals. These instrumentalities include conductors, buses, interfaces, and so on. These instrumentalities can be local, e.g. to connect modules that are physically close to each other, or over a network, for remote communication.

The chain is used in opposite directions for receiving and transmitting. In a receiving mode, wireless waves are received by antenna(s)810as signals, which are in turn processed successively by the various modules in the chain. Processing can terminate in any one of the modules. In a transmitting mode, initiation can be in any one of these modules. Ultimately, signals are transmitted internally, for antenna(s)810to transmit as wireless waves.

The architecture of system800is presented for purposes of explanation, and not of limitation. Its particular subdivision into modules need not be followed for creating embodiments according to the invention. Furthermore, the features of the invention can be performed either within a single one of the modules, or by a combination of them.

An economy is achieved in the present document in that a single set of flowcharts is used to describe methods in and of themselves, along with operations of hardware and/or software and/or firmware. This is regardless of how each element is implemented.

FIG. 9is a diagram showing a scenario900of an RFID reader910tasked with inventorying, i.e. reading the codes of RFID tags920. Reader910and tags920can be as in the prior art. In scenario900, reading is performed under easier conditions. Namely, there are relatively few tags, and they are not moving. Reading a tag code is sometimes informally written as reading a tag.

FIG. 10Ais a diagram along a TIME axis, which shows inventorying attempts1041,1042,1043, . . . . These attempts are what reader910would transmit with its wave912, in order to read tags920in scenario900. Inventorying attempt1041lasts between times T1and T2, and inventorying attempts1042,1043take place after that.

Each inventorying attempt1041,1042,1043, . . . includes at least one command. The commands, and the replies that the tags may give in response to them, are part of the applicable communication protocol, assuming that both follow the same protocol. Each set of commands and replies might result in reading a code of the tag, preferably after singulating the tag from the remainder of the tag population. Each inventorying attempt1041,1042,1043, . . . attempts to read all the tags.

FIG. 10Bis a diagram along a TIME axis, showing how the tags ofFIG. 9might be read, using the inventorying attempts ofFIG. 10A. Inventorying attempt1041results in reading of the tags according to reading curve1061. Similarly, inventorying attempts1042,1043result in reading curves1062,1063. According to comment1069, reading curves1061,1062,1063show the tags that are read in each attempt.

The shape of each of reading curves1061,1062,1063is approximate, and also shown in U.S. patent application Ser. No. 11/210,384, published as Document Number 2005/0280505A1, which is incorporated by reference in its entirety.FIG. 9of that other document shows a succession of inventory rounds, which are one inventorying attempt.FIG. 18Gof that other document shows the tags being read in a dashed reading curve (numbered1898in that document), as a Q parameter is being varied.

Returning to the present invention, for purposes of knowing about all the tags, a thicker cataloguing line1080shows which tags become known to reader910, and when. Tags become inventoried by being read at least the first time, at which time they also become catalogued. So, cataloguing line1080starts at a value NS which represents the number of tags that are to be inventoried, and is reduced to zero by the first reading curve1061alone. After that, the subsequent reading curves1062,1063add no new information, and cataloguing line1080remains at zero. In that sense, subsequent inventorying attempts1042,1043are redundant in this case. In practice, subsequent inventorying attempts1042,1043are provided to ensure that all tags have been read, even the harder ones to read that might be missed by first inventorying attempt1041.

In scenario900, the easier reading conditions are apparent because first inventorying attempt1041alone resulted in reading curve1061that read all the tags. Subsequent inventorying attempts1042,1043, contributed no new tags being inventoried. A more demanding scenario is now described.

FIG. 11illustrates a scenario1100, of RFID reader1110tasked with inventorying RFID tags1120. Scenario1100has more demanding reading conditions than scenario900, since there can be other readers1111nearby, and the population of tags1120is both larger, and could be moving, for example according to the direction of arrow1121. As such, some of tags1120are harder to read than others. Reader1110transmits a wave1112, which encodes commands of inventorying attempts1041,1042,1043, . . . .

FIG. 12is a diagram along a TIME axis showing how tags1120might be read by reader1110. Along the vertical axis, it can be seen that some of the tags in the population are easier to read, while others are harder to read. Four reading curves1261,1262,1263,1264are shown. According to comment1269, after reading curve1264, the tags may no longer be in the field of view (“FOV”), and any that had not been inventoried by then will be missed. Another term for FOV is reading zone.

A cataloguing line1280shows the progress in inventorying the tags. First reading curve1261will read all the easier tags. The reading curves1262,1263,1264of the subsequent attempts will contribute a few more of the harder to read tags. A problem is when not all have been inventoried by the time they leave the field of view. Another problem is when they have to all be inventoried at least twice, to guard against the inclusion of inadvertent stray reads, which could be one-time only.

FIG. 13is a diagram illustrating contents of a memory1350of an RFID tag made according to embodiments. Memory1350stores a code1352of the tag, which is also known as the tag code, and usually specifies the item that the tag is attached to. A number of codes may be used. For example, code1352may be the Electronic Product Code (“EPC”), as specified in the Gen2 Spec.

Memory1350also stores an inventoried flag1356. Flag1356is Boolean, in that it is capable of having only two states. Operations of the tag many flip the state from the one value to the other. Some of these operations may be inventorying operations, both in terms of selecting a subgroup of tags in the first place, and also in terms of commanding or not the state of flag1356to be flipped upon the tag becoming inventoried. Such an inventoried flag1356is specified, for example, in the Gen2 Spec as one of the S0, S1, S2, S3inventoried flags, whose values can be namely A or B. It should be noted that the Gen2 Spec permits only one of these flags to be used in a session for inventorying.

Memory1350further stores an inventoried indicator INV_ID1360. Inventoried indicator1360is updated in conjunction with backscattering the code. As such, it can help control whether a tag will participate in a subsequent inventorying attempt, or refrain to allow others a better chance. It should be noted that inventoried indicator1360is distinct from the Select Flag of the Gen2 Spec, which does not become updated in conjunction with backscattering the code.

While code1352, inventoried flag1356, and inventoried indicator1360are shown stored in memory1350, they are not necessarily stored in the same part of the memory. They can each be stored under different conditions. For example, code1352can be stored in a non-volatile memory that needs no power to be refreshed, even for years. In embodiments according to the Gen2 Spec, inventoried flag1356would have persistence as specified in its Table 6.14. And inventoried indicator1360has persistence as can be discerned by the person skilled in the art in view of this disclosure.

FIG. 14is a block diagram of a sample circuit showing how an inventoried indicator ofFIG. 13can be stored according to embodiments. The circuit is part of an overall circuit1424of components of the RFID tag circuit. Components1424include a tag controller1432, an energy source1434, and a register1436. Energy source1434can be volatile or non-volatile, and can provide a Power output to power register1436, and a State output to tag controller1432. Register1436stores INV_ID1460, which is input in tag controller1432, which in turn can determine whether the tag will participate in the inventorying attempt or refrain from it. In addition, tag controller1432can reset INV_ID1460, or input in register1436an original value for INV_ID1460. Moreover, in the embodiments where INV_ID1460is treated as a counter, tag controller1432can send a command for an operation. One such operation can be to decrement the counter. There can be other embodiments, for the same or different effects.

FIG. 15is a more detailed schematic circuit diagram1534for an embodiment of energy source1434ofFIG. 14. A switch1502can be closed to connect a tag power supply VDD to the Power output. A capacitor1504is connected to the same Power output; its size can determine the persistence of the power, after switch1502is opened, or VDD is lost. An Analog-to-Digital Converter (ADC)1506can sample the voltage on capacitor1504, and feed a resulting value to a comparator1508. Comparator1508can provide the State output, and also control opening and closing switch1502. There can be other embodiments, for the same or different effects.

FIG. 16is a conceptual diagram illustrating an embodiment where a register1650stores an inventoried indicator1660. Inventoried indicator1660becomes updated from a wave1612that is received from a reader. According to a comment1665, wave1612encodes a command that has a serial number SERIAL_NO of a group of inventorying attempts. This serial number SERIAL_NO is to be distinguished from other serial numbers, such as the tag code and the like. The serial number SERIAL_NO is learned from the command, and input in register1650as the new value INV_ID for inventoried indicator1660. In such embodiments, the reader plays a role in the tag's refraining behavior from the other attempts in the group.

FIG. 17is a conceptual diagram illustrating an embodiment where a register1750stores an inventoried indicator1760, and is part of a counter. Inventoried indicator1760may or may not become updated from a wave1712received from a reader. According to a comment1765, wave1712encodes a command that may or may not have an instruction for a counter, as will be described in more detail later in this document. In such embodiments, the reader may or may not play a role in the tag's refraining behavior.

FIG. 18is flowchart1800illustrating methods according to embodiments. The method of flowchart1800may be practiced by different embodiments of the invention, including but not limited to RFID tags, IC chips for RFID tags, and so on, which store in a memory a code, an inventoried flag capable of being flipped between two states, and an inventoried indicator, as described above.

Flowchart1800may be repeated a number of times, as a loop. For example, the tag may go through that loop once for every inventorying attempt, such as for the inventorying attempts described above. That is why, although the individual operations flowchart1800will be described in a certain order, they may take place in a different order.

At operation1810, a first attempt to read the code is detected. The first attempt can be an inventorying attempt, as per the above. The first attempt agrees with a current state of the flag, in that it calls for it exactly, or does not call for a condition that would contradict it.

At optional next operation1820, it is determined whether the inventoried indicator, as has been most recently updated, meets a participation condition. Examples of the participation condition will be described later in this document. The inventoried indicator can be updated at a later operation1850.

If the participation condition is not met, the tag will refrain, according to embodiments. This means that execution may return to operation1810, waiting to detect the onset of another inventorying attempt that agrees with a current state of the flag. Along with returning to operation1810, the tag may backscatter an error code, indicating that it is present but will not fully properly participate. Or it may backscatter nothing. If, however, the participation condition is indeed met, then the tag may participate plus update its inventoried indicator, as per the below.

At optional next operation1830, the tag becomes singulated from the population of tags it is with. This can be performed by the reader and the tag performing steps appropriate for the applicable communication protocol. Singulation will thus ensure that all the other tags in the population will not be responding, so that the reader can discern the forthcoming backscatter from the tag.

At next operation1840, the code is backscattered responsive to the first attempt.

At next operation1850, the inventoried indicator is updated in conjunction with backscattering the code. In terms of exact operation, the inventoried indicator can be updated after backscattering the code, or concurrently with it, or before it.

At next operation1860, the state of the inventoried flag is flipped or not, responsive to the first attempt. For example, the first attempt may include an instruction to flip or not flip the inventoried flag. Or it may not include such an instruction, but by its structure it might cause the inventoried flag to be flipped or not.

At optional next operation1870, the updated inventoried indicator becomes reset, such that the inventoried indicator now meets the participation condition. This operation may also take place at other times in flowchart1800, for example if after operation1820it has been determined to refrain from participating.

Resetting may take place in any number of ways. In some embodiments, this can be automatic after enough time passes. For example, there can be a preset time that elapses from an event, and then there is reset. Alternately a suitable Reset command can be receiving wirelessly.

Execution then can return to operation1810. Or, since operation1870is optional, execution can return to operation1810after operation1860, instead. Operation1810may be reached either without losing power in the tag since operation1860was executed, or with losing and regaining power.

Once back at operation1810, a second inventorying attempt can be detected, which can agree with a current state of the flag. Then, again according to operation1820, it is again determined whether the inventoried indicator, updated at operation1860, meets the participation condition. It might not meet it, due to the update. If it does, then the above sequence of operations can be repeated, and so on.

In some embodiments, the reader also transmits a serial number in association with the first attempt, and the tag receives it. The serial number can be transmitted and received in any suitable way. One suitable way for transmitting it is via a Select command or a BlockWrite of the Gen2 Spec, as is described later in this document.

Then the inventoried indicator can be updated by being set to a new value. The new value can be the serial number itself, or another number determined from the serial number. In some of these embodiments, the participation condition can refer to whether the updated inventoried indicator differs from the new value. So, when a new attempt is detected, if it corresponds to the same serial number, the tag will know to refrain, and the participation condition can be defined accordingly so as to effectuate the refraining, for example by returning to operation1810directly from operation1820. If the new attempt corresponds to a different serial number, there will be participation. The new attempt could be from a different reader, or from the same reader that wants to inventory again all the tags in its field of view. The latter embodiment can take place if the reader is confident that it has inventoried all tags, and does not need any of them to refrain from the second attempt.

The serial number can be specific to a group of forthcoming attempts by a reader. Plus, if two readers are cooperating, they could use the same serial number. This way, once a tag is inventoried by one of the readers, it will refrain from being read also by the other. The serial number could also be specific to the reader, which is useful if two readers have overlapping fields of view. This way, once a tag is inventoried by one of the readers, it will refrain from being read by it. But it will not refrain from being read by the other reader. In some of these embodiments, the tag can maintain a list of such serial numbers, so as to be able to refrain from being read by multiple readers.

FIG. 19is a diagram1900along a TIME axis, similar toFIG. 12, but which results from embodiments. Diagram1900illustrates tags being read by reading curves1961,1962,1963,1964,1965,1966,1967. The tags read by each one of these reading curves do not participate in the subsequent ones, thus enabling tags that are harder and harder to be searched for and found. Accordingly, a cataloguing line1980starts at NS and comes down to zero rather quickly, while that ofFIG. 12never did. InFIG. 19, finding all the tags proceeds faster, because each subsequent inventorying attempt does not have to read again tags that have already been found. The contrast is illustrated by repeating times T1, T3in bothFIG. 12andFIG. 19. The better performance according to the invention was made possible inFIG. 19because tags, once inventoried, refrained from participating.

In fact, in this example, reading curve1967returned no new tags. As such, there was a Reset command1970, and then another reading curve1971, starting again from all the tags.

The reading curves and cataloguing line ofFIG. 19can be caused by any number of operations by the reader. Two alternative examples are now described, with reference toFIGS. 20 and 21.

FIG. 20is time diagram showing repeated inventorying attempts that may be transmitted according to embodiments and received, so as to generate the result ofFIG. 19. A group of inventorying attempts2041,2042,2043,2044,2045,2046,2047has an associated serial number SN1. This serial number SN1is transmitted via an earlier command2040, in the context of the refraining feature. Attempts2041,2042,2043,2044,2045,2046,2047could have generated reading curves1961,1962,1963,1964,1965,1966,1967, respectively.

According to comment2069, attempt2047returned no new tags. A command2050can transmit a second serial number SN2for the next forthcoming group. Command2050can operate as Reset command1970. Then another attempt2051can result in another reading curve1971, and so on.

FIG. 21is another time diagram showing repeated inventorying attempts that may be transmitted according to embodiments and received, so as to generate the result ofFIG. 19. A group of inventorying attempts2141,2142,2143,2144,2145,2146,2147has an associated serial number SN1. This serial number SN1is transmitted within each one of these attempts. Attempts2141,2142,2143,2144,2145,2146,2147could have generated reading curves1961,1962,1963,1964,1965,1966,1967, respectively.

According to comment2169, attempt2147returned no new tags. Then another attempt2151can result in another reading curve1971, and so on. Attempt2151can include the second serial number SN2of its own group, and thus no Reset command is needed.

Returning toFIG. 19, it will be observed that each tag was inventoried only once, and tags were not read again until there was confidence that all tags had been inventoried. Sometimes, however, it is desired to read tags more than once, for example so as to validate against a tag code arising spuriously. In some sample instances, a rule can be implemented that, unless a tag is read redundantly, for example at least twice, it will be considered a stray read, and thus not counted. The invention can help in such instances, by having tags refrain from being counted more than twice. Examples are now described, which can be different from where the inventoried indicator was a serial number.

In some embodiments, the inventoried indicator is a number, which is stored in a counter. For example, register1436would store that number. Updating the inventoried indicator can be performed by adjusting the number in the counter, and the participation condition is that the number in the counter has not reached a limit. This can be implemented in many ways. For example, the number in the counter can be adjusted by being incremented up to some limit. Or, the number in the counter can be adjusted by being decremented down to a limit. In some of these embodiments, that limit can be zero.

In some embodiments, this feature operates autonomously. In others, assistance from the reader is called for. The reader can enable the feature, or disable it, if that is called for. Optionally, the reader can transmit and the tag can receive a participation parameter. Then a number initially stored in the counter, or the limit, can be determined from the received participation parameter. The participation parameter can be received via a Select command or a BlockWrite of the Gen2 Spec, or other suitable commands.

The number in the counter and the limit thus determine in how many attempts the tag will participate, before it starts refraining. For example, if the number in the counter starts from 1, and counts down to zero, the tag will participate only once, and the profile ofFIG. 19will result. A different example is now described, where each tag participates twice.

FIG. 22is a time diagram illustrating tags being inventoried, where some tags are harder to read than others, but where also the tags limit themselves to participating in only two inventorying attempts and then refrain, according to embodiments.FIG. 22is a diagram2200along a TIME axis, similar toFIG. 12, but which results from embodiments. Diagram2200illustrates tags being read by reading curves2261,2262,2263,2264,2265,2266,2267,2268. After each tag participates in two of these reading curves, it refrains from participating in the subsequent ones, thus enabling the harder to read tags to be found. Accordingly, a cataloguing line2280starts at NS and comes down to zero. This took longer time than inFIG. 19, but still less time than inFIG. 12. The reading curves and cataloguing line ofFIG. 22can be caused by any number of operations by the reader, as will be discerned by the reader in view of the present disclosure.

In some embodiments, a tag refrains from being inventoried in subsequent rounds as per the above. In others, it does that only when the tag is in an enabled state, as opposed to a disabled state. An example is now described.

FIG. 23is an optional partial state diagram2348of a state machine of a tag having an electrical circuit as shown inFIG. 4. State diagram2348can be implemented by a state machine in processing block444. State diagram2348includes an enabled state2365and a disabled state2385, which can be states as described above. The tag can transition between enabled state2365and disabled state2385in any number of ways. For example, it can be in one of these two states when powered initially, and then transition if a condition is met. The condition can be that enough time has passed from an event. In addition, the condition can be that an Enable Refraining command2360and/or a Disable Refraining command2380are received, which cause the state of the tag to transition between enabled state2365and disabled state2385.

In some embodiments, enabled state2365and disabled state2385are provided in a way that does not define additional states in the underlying protocol. For example, for the Gen2 Spec, the initial Ready state can be disabled state2385, while one or more of the other states can be enabled states2365. Or some of the other states can also be characterized as disabled state2385.

In other embodiments, either one or both of enabled state2365and disabled state2385can be provided as states different from, and in addition to what is required by the Gen2 Spec.

FIG. 24is a diagram illustrating commands that may be transmitted by a reader according to embodiments. A wave2412is a special case of wave112ofFIG. 1. An Enable Refraining command2460can be sent first, for example to have the effect of Enable Refraining command2360. An inventorying with refraining command2470can be sent next, for example to have the effect of standalone command2040,2050,2140, or be a variation of a command in attempt2041or2141. Then a Disable Refraining command2480can be sent, for example to have the effect of Disable Refraining command2380.

As will be realized, commands2460,2470,2480can be configured in any number of ways. For example, if Enable Refraining command2460is provided, it can be separate from command2470. Preferably, these are configured as separate standalone commands, each occurring at a single one of the communication sessions such as those of time interval312ofFIG. 3. In addition, the tag need not backscatter a reply to any one of them individually.

In addition, command2470, plus optionally commands2460and2480, may be used among other commands that will be transmitted to the tag in question, and possibly other tags. Equally, the optional first and second replies will be among other replies backscattered by the tag in question, and possibly other tags.

FIG. 25is flowchart2500illustrating a method according to other embodiments of the invention. The method of flowchart2500may be practiced by different embodiments of the invention, including but not limited to RFID reader systems, readers, related components, software, and so on. The method is for communicating with an RFID tag storing a code, an inventoried flag capable of being flipped between two states, and an inventoried indicator, as per the above. In addition, details of the method of flowchart2500can be also understood with reference to what was written above.

At operation2510, a first attempt to read the code is caused to be transmitted wirelessly, which agrees with a current state of the inventoried flag, and includes a first participation parameter. The first participation parameter can be any suitable parameter. In some embodiments, for example, it is a serial number that is associated with the first attempt, as per the above. In other embodiments, the inventoried indicator includes a number stored in a counter, which is determined from the received participation parameter. In other words, the first participation parameter is used to help determine the number in the counter. The first participation parameter can be caused to be transmitted in any suitable way, for example as part of a command, a parameter of a command, and so on. For implementations of the Gen2 Spec, such can be a Select command, a BlockWrite command, and so on.

At next operation2520, the backscattered code is received from the tag responsive to the first attempt. Concurrently with the first attempt, the tag may further update the inventoried indicator in conjunction with backscattering the code, and flip or not the state of its inventoried flag, as also per the above.

At next operation2530, a second attempt to read the code is caused to be transmitted wirelessly. This second inventorying attempt agrees with a current state of the inventoried flag.

At optional next operation2540, it is determined whether a participation condition is met. The participation condition refers to whether the updated inventoried indicator differs from the first participation parameter. The inventoried indicator may have been updated concurrently with receiving the backscattered code at operation2520.

If, at operation2540, the participation condition is met, then at optional next operation2550, the backscattered code is received responsive to the second attempt, as it was also received in operation2520. Else, at optional next operation2560, the backscattered code is not received, as per the above.

Returning toFIG. 24, each one of commands2460,2470,2480can be constructed in any number of ways. In some instances, they can be considered as custom commands as not being specified in a particular communication protocol. In some instances they would be standalone commands, made by a sequence of bits chosen so that they do not conflict with other commands of the protocol. In other instances, they can be commands with a custom payload. Such commands can be known to the protocol or not, and the payload can be used to distinguish among different custom commands, and optionally further transfer a parameter for the commands.

When commands are used that are known to the protocol, a section of their payload can be advantageously used for the purpose of implementing a custom command, such as commands2460,2470,2480. Such a section in the payload can be a mask field, according to embodiments. For the Gen2 Spec, two such commands are the Select command and the BlockWrite command. Between these two candidate commands, it should be considered that the Select command can be transmitted before or after a tag is singulated out of its population, while the BlockWrite is better suited for singulated tags. In addition, the BlockWrite command is optional to the Gen2 Spec, and the tag would probably have to have a controller that can accept it.

Each one of commands2460,2470,2480can thus be constructed as an implementation of this Select command or the BlockWrite command. An example is now described in terms of the Select command, but would apply equally to the BlockWrite command.

FIG. 26Ais a table illustrating the fields of the Select command of the Gen2 Spec. Version 1.1.0 of the Gen2 Spec is hereby incorporated by reference in its entirety. The fields of this Select command are explained in more detail in the above mentioned Gen2 Spec. In addition, the implementation of this Select command can have a custom payload so that it operates as any one of commands2460,2470,2480and/or another custom command.

FIG. 26Bis a table illustrating how a number of custom commands can be enabled in a reader and a tag. EBV stands for Extensible Bit Vector. The Mask Field can be partitioned as shown, into two primary subfields, named FEF and FCF.

The Feature Enabling Field (FEF) enables the tag to verify that it is a proper recipient for the command, by comparing the transmitted FEF value against a value in Membank. In this case, Membank can be EPC, TID or USER memory. As can be seen, the FEF can be further partitioned into subfields, for better clarity. Such subfields can include a Class Identifier, the MDID, and an Indicator Bit.

The Class Identifier can be two bits. For example, EPCglobal can correspond to a value of 10. This would allow the custom command to apply, for example, only to EPCglobal tags.

The MDID is the tag manufacturer's ID, which is stored in the tag's TID memory. For Impinj tags, this number is 000000000001 or 100000000001. The MDID allows a reader to select tags of only the manufacturer of interest. So, even if this Select command is transmitted and received before singulation, the Select command can select also according to the tag manufacturer's ID. This will cause the manufacturer's tags to be selected, and thus the reader can ensure prior knowledge of the tag manufacturer's identification.

The Indicator Bit can be set to 0 or 1. In the Gen2 Spec, a tag model number follows the MDID. A bit of this model number can serve as the Indicator Bit, and can be interpreted as follows: If it is 0, the tags can interpret the command as an “ordinary” Select, and execute it per the Gen2 spec. Else, if it is 1, the tags can interpret the Select command as a custom instruction, and execute according to the FCF.

The Feature Command Field (FCF) can have a command code that indicates the number of the custom instruction. For example, a command code of 00000 could be the custom command. This permits31possible custom commands. In addition, a command code of 11111 could indicate an extended command code that extends into the subsequent data field.

The data field can contain data needed to implement the custom instruction, if any. Not all commands will use it. The data field can be variable in size. Its meaning will derive from the command codes.

In some embodiments, the tag may ignore the Target and Action field in the Select command, depending on whether these fields are relevant to the CI. In other embodiments, the tag may also set the appropriate flag.

In preferred embodiments, the entire Select command must be valid for the tag to accept and execute the custom command. That means valid values for Membank, Length, Pointer, Mask, CRC-16, etc. An example is now described.

FIG. 26Cis a table showing sample values that can be used for the table ofFIG. 26B. These could be used for a custom command. The Membank has a binary value of 10 point to the TID memory. The pointer has a hex value of 06 h points to the last two bits of the class identifier. The length has a hex value of 14 h points to a length of 20 bits that follow thereafter.

Everything described above in terms of readers and reader components finds some correspondence with tags and tag chips. In some instances, some of the above also describe features and behavior of tag chips.

Numerous details have been set forth in this description, which is to be taken as a whole, to provide a more thorough understanding of the invention. In other instances, well-known features have not been described in detail, so as to not obscure unnecessarily the invention.

The invention includes combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. The following claims define certain combinations and subcombinations, which are regarded as novel and non-obvious. Additional claims for other combinations and subcombinations of features, functions, elements and/or properties may be presented in this or a related document.