RFID tag based discrete contact position indication

An RF based state indicator for indicating the state of a control device is provided. The RF-based state indicator indicates the position of a control mechanism by using the position of the control mechanism to enable or disable an RF tag. An RF reader acquires RF transmitted data from enabled RF tags and uses the data to indicate or control an operation aspect of a device.

BACKGROUND

The invention relates generally to the field of switches and similar devices used to control application of power to electrical loads. More particularly, the invention relates to the use of radio frequency identification (RFID) tags to indicate the state of an input device, such as a pushbutton, an electrical contact, a relay or contactor, and so forth.

In the field of electronics, a wide range of control devices is used for controlling the delivery of power to a load. Such control devices may include various switches, relays, contactors and disconnects to control load power, circuit breakers to protect electrical circuits from overload, and pushbuttons and selector switches to facilitate user control of power circuit operation. Additionally, a variety of electrical devices are known and currently available for indicating the state of a control device. For example, an auxiliary contact is often coupled to a contactor so that the auxiliary contact produces an auxiliary signal, a low power electrical signal that indicates whether the contactor is open or closed. The auxiliary signal may be coupled, as an input signal, to other components within a power control or monitoring system. For example, the auxiliary signal may be used to turn on or off an indicator light, or some other component within the power electronics system.

As power control systems and the logic required to control these systems become more complex, the number of state indicators increases, and the wiring coupled to the state indicators also increases. The increased wiring, in turn, leads to increased costs due to hardware requirements, connection labor and wiring maintenance. For example, control devices are often disposed within and on the doors of metal enclosures for load control purposes, with wires running between the door-mounted devices and internal devices. An increase in the number of wires increases maintenance problems due to wiring failure and inconvenient tethering of door-mounted devices with internal devices. Additionally, because there is a limit to how many wires can be placed under the common screw-terminal connectors, hardware is often added to control devices in the form of additional contacts driven by a mechanical or electromechanical shaft called an operator. Furthermore, each electrical connection creates the potential for vibration induced failure. Therefore, labor, maintenance and material costs could be reduced if the discrete wired state indicators could be replaced with wireless state indicators.

The use of wireless state indicators, however, presents the difficulty of finding a suitable power supply. Often times a power supply is not available from the control device. Even when power is available, in the form of load power, the conversion from high voltage to low voltage adds additional cost. Batteries, on the other hand, incur additional maintenance costs due to the need for frequent replacement, and large batteries may interfere with control devices housed within the limited space of the metal enclosures. Furthermore, power scavenging techniques (based on vibration, or light or thermal gradients) typically provide too little power to achieve suitable control update rates, are too large, or depend on unreliable sources.

Therefore, it may be advantageous to provide an improved state selection or indicator device. In particular, it may be advantageous to provide a state selection or indicator device that communicates wirelessly and employs a power supply that is reliable, maintenance free, and allows acceptable control update rates.

BRIEF DESCRIPTION

Embodiments of the present invention use RFID tags as binary state indicators to indicate the state of power control devices and user input indications. An embodiment of an RFID tag, in accordance with the present invention, includes an RFID chip, which contains identification information and an RF antenna that is selectively coupled to or decoupled from the RFID chip to indicate the binary state of a power control device. An embodiment of a control system, in accordance with the present invention, includes one or more RFID tag readers electrically coupled to load control circuitry and one or more RFID tags in wireless communication with the RFID tag readers to effect changes in the state of the loads.

DETAILED DESCRIPTION

Turning now to the drawings, and referring first toFIG. 1, an exemplary control system is illustrated and designated generally by reference numeral10. The control system10may include a plurality of RFID state selectors or indicators12(referred to herein simply as state indictors). AlthoughFIG. 1depicts two RFID state indicators, it should be noted that the present invention is not limited to any particular number of RFID state indicators. In embodiments of the present invention, the RFID state indicators12are input devices used to facilitate user control of some operational aspect of the control system10, as will be explained below. In other embodiments, the RFID state indicators12are coupled to components within the control system10such as to provide an indication of the operational state of the control system10.

Also included in the control system10is a reader16. The reader16may be any device known to those of ordinary skill in the art for communicating with, or “reading,” RFID tags. Readers are also commonly known as interrogators. The reader16iteratively acquires data from the RFID state indicators12, by transmitting a power/interrogation signal18. As described below, the RFID state indicators12may or may not emit a return signal14to the reader16in response to the power/interrogation signal18. The detection or non-detection of a return signal14corresponding with each RFID state indicator12informs the reader16of the binary state of each RFID state indicator12.

The RFID state indicator12includes an RFID tag22. The RFID tag22includes an antenna24and a circuit26. The antenna24is both a receiving antenna and a transmitting antenna, designed to resonate at a particular frequency that corresponds with the communication frequency or frequencies of the reader18. The electrical energy received by the antenna24from the reader16through the power/interrogation signal18serves to power the circuit26. In certain embodiments of the present invention, the circuit26that holds a small amount of coded information, such as, for example, identification data, make and model, year of manufacture, etc. The circuit26is considered “passive” in that it does not have an independent power source and it does not initiate transfer of the information except in response to the signals from reader16. If the circuit26is coupled to the antenna24, the power/interrogation signal18from the reader16will power the circuit26and cause the circuit26to generate a control signal encoded with the data stored on the circuit26.

The RFID state indicator12also includes an operator30, which selectively couples or decouples the antenna24from the circuit26(or that completes a circuit required to define the antenna). Whether the RFID tag22emits a return signal in response to the power/interrogation signal18depends on the state of the operator30. In certain embodiments of the present invention, the RFID tag22is normally open, as shown inFIG. 1. As such, the antenna24is decoupled from the circuit26by an interruption28, a small insulative gap on one side of the circuit26. The interruption28causes the circuit26to be inoperative. In the embodiment illustrated, the interruption actually opens the loop required to form the antenna. If the operator30is brought into contact with the RFID tag22, however, the interruption28is bridged by an electrical conductor, causing the circuit26to become operative. The operator30may be coupled to a control device, such as, for example, a pushbutton or a switch, thereby allowing a user to enable or disable a particular RFID tag22. Alternatively, the operator30may be coupled to a contactor so as to provide an indication of whether a particular circuit within the system is powered, or more generally, to indicate the operative state of the system.

Information regarding the state of the RFID state indicator12is collected electronically by the reader16by sending out a power/interrogation signal18. If the power/interrogation signal18causes the antenna24to resonate, and if the antenna24is electrically coupled to the circuit26, the electrical energy received by the antenna24will power the circuit26, thereby inducing the circuit26to modulate its antenna with its coded information creating a reflected return signal14back to the reader16. In response to each power/interrogation signal, therefore, all of the operative RFID state indicators12within communications range follow protocol instructions encoded in the power/interrogation signal and if requested send a return signal14that carries, among other things, identification information. If an RFID state indicator12responds with a return signal14, the reader16is thereby informed that the particular RFID tag22corresponding with the transmitted identification information is operative, meaning that the particular input device coupled to the RFID tag22, e.g. pushbutton, switch, etc., has been engaged. The information thus gained by the reader16can then be used to control some part of the control system10. In other words, the detection of a return signal14with a particular identification code may indicate that a particular part of the control system10, which corresponds with the identification code, should be engaged or disengaged (e.g., turned on or off.) It should be noted that, in embodiments of the present invention, the “on” state is signified by the detection of a return signal14from the RFID state indicator12. In alternate embodiments, the “on” state is signified by the non-detection of a return signal14from the RFID state indicator12.

Also included in the control system10is processing circuitry36. In one embodiment, the processing circuitry36is used to control the reader16. For example, the processing circuitry36may be used to adjust the frequency or intensity of the power/interrogation signal18, to control a read-cycle rate of reader16, or to trigger individual read cycles. Furthermore, processing circuitry may also be used to process the RFID state data received by the reader16. For example, the reader16may send RFID state data to the processing circuitry36after each read cycle. The processing circuitry36may then respond to the RFID state data by initiating an electronic output that manipulates the control system10in accordance with the desired operational state as represented by the RFID state data received. The processing circuitry36, therefore, includes a means of interpreting the RFID state data and associating the RFID state data with a desired operational state of control system10. In this regard, the control system10may optionally include a memory38coupled to the processing circuitry36. The memory38may, for example, contain a database that associates the identification information encoded in each RFID tag22with a particular controlled load42. Additionally, although some or all of the programming logic by which the processing circuitry36operates could be hardwired into the processing circuitry36, the memory38could also be used to hold a software program which determines, at least in part, how the processing circuitry36operates.

Also included in the control system10is driver circuitry40. The driver circuitry40can include any means known in the art for powering components of a control or monitoring system. The driver circuitry40is electronically coupled to the processing circuitry36, the load42and a state indicator48, in this case an indicator light. The driver circuitry40receives an input signal from the processing circuitry36and optionally delivers a control signal to the load42and/or the indicator light48, thereby powering the load42and/or the indicator light48, depending on the state of the RFID state indicators12. In the embodiment shown inFIG. 1, the load42includes a motor46and switch gear44, such as, for example, a contactor. As stated above, however, the present invention is not limited to a particular type or combination of load components.

Embodiments of the present invention also include a network34. The network34may include any type of communications network such as a local computer network. The network34can be used in conjunction with the processing circuitry36, or as an alternate technique, for controlling the control system10. For example, according to one embodiment, the reader16may send RFID state data to the network34through the interface32. Some or all of the acquired RFID state data may then be routed to the processing circuitry36or to the processor50. If the RFID state data is routed to the processor50, the processor50then processes the state data and sends control signals to the driver52, which, in turn, delivers load power or a control signal to the load54, thereby turning the power supplied to the load54on or off depending on the user desire and the system programming, as indicated by the RFID state data. According to another embodiment of the present invention, software and configuration data can also be downloaded from the network34to the processing circuitry36or the processor50. According to another embodiment, the network34is coupled to a computer system or other electronic device that includes a display, and RFID state data is used to display the current operational configuration of the control system10.

It should be recognized that a control system in accordance with the present invention may take on a variety of configurations and include a wide variety of electrical devices, many of which are not depicted. For example, embodiments of the present invention may include several motors, switches, valves, pumps, indicator lights, alarms, breakers, etc. Additionally, some of the components depicted inFIG. 1may not be necessary, such as the interface32or the network34. The present invention is not intended, therefore, to be limited to the embodiment depicted inFIG. 1. In fact, RFID state indicators in accordance with the present invention can be adapted for use in any system that uses binary inputs or outputs.

Turning now toFIG. 2 and 3, an exemplary embodiment of an RFID state indicator is shown.FIG. 2depicts an RFID state indicator12that includes a housing20an operator30, and an RFID tag22. The operator30is a pushbutton-style operator that includes a body64, conductive extensions66and68, and a biasing member70, such as a spring, that biases the actuator30away from the RFID tag22. The RFID tag22includes an antenna24, electrical contact pads56and68separated by interruptions28, and a circuit26. In the embodiment shown inFIG. 2, the RFID tag22is inoperative because the interruption28prevents the antenna24from electrically coupling to the circuit26. Because the RFID tag22is inoperative, the circuit26will not power up or send a return signal in response to a power/interrogation signal sent by an RFID tag reader. In the embodiment shown inFIG. 3, however, the operator30has been depressed, and the conductive extensions66and68have bridged the interruptions28between the electrical contact pads56and58. Thus, the RFID tag22shown inFIG. 3has become operative. Therefore, if an RFID reader sends a power/interrogation signal of the proper frequency, circuit26will send a return signal containing at least the identification information stored on the chip.

It should be recognized that in the embodiment shown inFIGS. 2 and 3, the lack of a return signal could indicate a disengaged pushbutton or a failure of the RFID tag22to operate properly. Therefore, depending on the specific application, it may be desirable to include a second RFID tag that will indicate the normal or disengaged position of the actuator30. In this regard, an embodiment of the present invention may include a second RFID tag that is enabled when the actuator30is in the disengaged position shown inFIG. 2. With two RFID tags, a return signal will be expected whether the pushbutton is engaged or disengaged, and a failure to detect a return signal indicates a failure of an RFID tag or a failure to read an RFID tag, facilitating detection of failures.

RFID tags in accordance with the present invention may include various embodiments not depicted byFIGS. 2 and 3. Regarding the antenna24, embodiments of the present invention may include any form of antenna known by those of ordinary skill in the art. For example, antenna24could be electrically and/or magnetically excited and may include one or more conductive loops, a conductive spiral, a conductive dipole or monopole, an inductor, a capacitor, or some combination thereof. The antenna24may also be printed or etched onto a substrate material or may be comprised of conductive wire. Additionally, the antenna24may include a material designed to alter the resonance characteristics of the antenna such as a ferromagnetic material. The design of the antenna24will be an ordinary engineering task involving the selection of a particular substrate, substance, geometry, etc. that is optimal for the particular design requirements that are chosen for a particular implementation of the present invention such as frequency, directionality, gain and power handling.

Additionally, embodiments of the present invention may include several alternative configurations for isolating the circuit26from the antenna24. For example, in some embodiments, an electrical interruption is included on only one side of the circuit26. Alternatively, one or more electrical interruptions may be placed at any position along the length of antenna24. Additionally, in some embodiments, the interruptions28will be as close as possible to circuit26to lessen the degree of residual coupling that may occur due to the short conductive segments that may protrude from the circuit26depending on the location of the interruptions.

Furthermore, in addition to electrically isolating the circuit26from the antenna24, embodiments of the present invention include an RFID tag22that is made inoperative by preventing the antenna24from resonating in response to the power/interrogation signal emitted by the reader16. For example, the operator30may bring one or more additional conductors into proximity or contact with the antenna24, thereby altering the resonant characteristics of the antenna24such that it will not effectively resonate at the frequency transmitted by the reader16. In this way, the RFID tag22is disabled because the antenna24will not transmit electrical power to the circuit26.

Additionally, RFID tags in accordance with the present invention may be normally operative or normally inoperative. In other words, if an RFID tag is normally operative, the circuit26and the antenna24will be electrically coupled and operative without the interposition of the operator30, and the engagement of the operator30will disable the RFID tag in some way. On the other hand, if an RFID tag is normally inoperative, the circuit26and the antenna24will be electrically decoupled or, in some other way, disabled without the interposition of the operator30, and the engagement of the operator30will enable the RFID tag.

Regarding the circuit26, the circuit26can be any type of semiconductor circuit known in the art, such as, for example, a CMOS integrated circuit. Although the circuit26will ideally be passive, i.e. not requiring a power source other than the power/interrogation signal, the circuit26could optionally be active, or semi-passive. In other words, the circuit26could be fully or partially powered by a battery or some other power source other than the reader16. Additionally, the circuit26may hold and transmit a range of useful information, such as, for example, RFID tag model, style, serial number, date of manufacture, physical location, etc. This data may then be used to maintain the RFID tags or replace RFID tags. For example, the data may be used to indicate the location of a particular RFID tag and whether a particular RFID tag is old or outdated or may need to be replaced as part of regular maintenance. To hold the data, the circuit26may include any form of electronic memory known in the art including read-only memory, writable memory or some combination of both.

Turning now toFIG. 4, an exemplary embodiment of a rotary device72, in accordance with the present invention, is depicted. The rotary device72comprises three normally inoperative RFID tags74,76and78aligned along an arc80, and a rotary operator82anchored at the radial center of the arc80. The operator82is rotatable, such that the conductive portions of the operator82selectively enable one of the RFID tags74,76, or78. The operator82, may be human operated, or may be mechanically coupled to another rotating element (not depicted) whose position is to be determined by the rotary device72. The operator82may also include one or more detent mechanisms to hold the operator82more securely in contact with one of the RFID tags74,76or78. Additionally, the rotary device72may include any number of RFID tags aligned along the arc80. In embodiments of the present invention, the rotary device72includes one or more additional arcs, not depicted, along which additional RFID tags are aligned. The additional RFID tags may be staggered radially so that only one RFID tag is enabled for any position of operator82, or the additional RFID tags may be radially aligned so that more than one RFID tag is enabled for a particular position of operator82.

Turning now toFIG. 5, an exemplary embodiment of an auxiliary signal device84is depicted. The auxiliary signal device84may be a relay, contactor, disconnect switch or any other device that controls a primary current path via an input signal. The auxiliary signal device84includes a control terminal88coupled to a controller96, which controls the position of an operator92by inducing a current flow in a coil94. The auxiliary signal device84also includes a moveable contact100connected to an operator92through a linkage98, such that movement of the operator92, will bring the moveable contact100into contact with a stationary contact102, thereby completing an electrical path between a set of output terminals90.

Also included in the auxiliary signal device84are two normally inoperative RFID tags108and114. Depending on the position of the operator92, RFID tag108is made operative by conductive extensions104and106, or RFID tag114is made operative by conductive extensions110and112. As depicted inFIG. 5, the current position of the operator92is such that RFID108is operative and RFID tag114is inoperative. In the embodiment depicted inFIG. 5, a power/interrogation signal from an RFID tag reader would power RFID tag108, and RFID tag108would send a return signal, while RFID tag114would remain silent. The return signal will, therefore, indicate that auxiliary signal device84is off, i.e. output terminals90are decoupled. If a control signal is applied to the control terminals88, the operator92will move downward, bringing the movable contact100into contact with the stationary contact102, completing the circuit between the terminals90. Furthermore, conductive extensions104and106will move out of contact with RFID tag108, disabling RFID tag108, and conductive extensions110and112will move into contact with RFID tag114, enabling RFID tag114. With this new actuator position, a power/interrogation signal from an RFID tag reader will power RFID tag114, and RFID tag114will send a return signal, while RFID tag108will remain silent. The return signal will, therefore, indicate that auxiliary signal device84is on, i.e. output terminals90are coupled.

In certain embodiments of the present invention, the auxiliary signal device84includes only one RFID tag, wherein the enablement of the RFID tag indicates one actuator position and the disablement of the RFID tag indicates the opposite position. Using one RFID tag may, however, lead to uncertainty about whether the lack of a return signal was due to the disablement of the RFID tag or failure of the RFID tag to operate properly. Therefore, the use of two RFID tags, as depicted inFIG. 5, provides a higher level of assurance of the state of auxiliary signal device84, because at least one return signal will always be expected and the lack of a return signal will generally result from device failure or a failure to read either RFID tag.

Turning now toFIGS. 6 and 7, an embodiment of a short-circuiting RFID state indicator116is shown. The short-circuiting RFID state indicator116includes an RFID tag with a circuit120and an antenna118. Because the electrical coupling between the antenna118and the circuit120is built into the RFID tag, the RFID tag is normally operative and thus does not require the interposition of a conductive element to be enabled. Also included in the short-circuiting RFID state indicator116is an operator30that includes conductive extensions66and68and a conductive link122. As long as the operator30remains disengaged, the RFID tag will remain operative and will, therefore, send a return signal14. If, however, the operator30is moved into contact with an exposed conductive portion of the antenna118of the RFID tag, as shown inFIG. 7, the conductive extensions66and68and the conductive link122will create a short circuit across the circuit120, thereby decoupling the antenna118from the circuit120. As discussed above, other means of disabling an RFID tag may be envisioned. For example, in embodiments of the present invention the interposition of an operator serves to shield the antenna118. In other embodiments, the interposition of an operator changes the geometry and hence the resonance characteristics of the antenna118such that it no longer effectively resonates at the frequency emitted by the reader. In another embodiment, the conductive elements66and68and conductive link122are placed permanently on the tag instead of on the operator and the conductive link122is composed of a magnetic reed switch that selectively enables and disables the RFID tag by movement of a magnet carried on the tag end of the operator.

As described above, the device of the invention allows for altering performance of the antenna and/or of the circuit coupled or couplable to the antenna so that the reader or interrogator may read or be prevented from reading the data in the circuit, and thereby gather an indication of the state of the device (e.g., position of the operator). As noted above, this may be done in a variety of manners. For example, the operator may complete or interrupt a conductive path defining the antenna (e.g., making or breaking a loop forming the antenna), or may short or unshort the antenna (e.g., connect or disconnect the antenna with another component or conductive path). Because the antenna operates by returning a signal to the interrogator, the operator may alter an electromagnetic property of the antenna to allow or prevent such transmission, or may shield or unshield the antenna, or change a resonant frequency of the antenna. Moreover, two or more such antenna may be utilized to provide a multi-state device in which signals from one circuit available from one antenna indicate a first state, and signals from a further circuit available from another antenna indicate a second state.