Abstract:
An access control system having an energy-saving optical presence sensor system is provided. The access control system includes a relatively lower operating power object presence sensor system for optically sensing the presence of a token as well in addition to a relatively higher operating power token reader for reading the token. The token reader remains unpowered until a token is detected by the object presence sensor system, which is preferably always powered. Once an object is detected by the object presence sensor system, power is supplied to the token reader and the token is read. After the token has been read, power ceases to be applied to the token reader, although the object presence sensor remains powered.

Description:
RELATED APPLICATIONS 
     The present application claims priority to the following applications: application Ser. No. 10/261,933, entitled “RF Channel Linking Method and System” filed Sep. 30, 2002; application Ser. No. 10/262,207, entitled “Energy Saving Motor-Driven Locking Subsystem” filed Sep. 30, 2002; application Ser. No. 10/262,509, entitled “Cardholder Interface for an Access Control System” filed Sep. 30, 2002; application Ser. No. 10/262,196, entitled “System Management Interface for Radio Frequency Access Control” filed Sep. 30, 2002; application Ser. No. 10/262,194 entitled “Power Management for Locking System” filed Sep. 30, 2002; application Ser. No. 10/262,507, entitled “General Access Control Features for a RF Access Control System” filed Sep. 30, 2002; application Ser. No. 10/262,077, entitled “RF Wireless Access Control for Locking System” filed Sep. 30, 2002; application Ser. No. 10/262,508, entitled “Maintenance/Trouble Signals for a RF Wireless Locking System” filed Sep. 30, 2002; application Ser. No. 10/262,249, entitled “RF Dynamic Channel Switching Method” filed Sep. 30, 2002, and U.S. Provisional Patent Application No. 60/537,850, entitled “Access Control System With Energy-Saving Optical Token Presence Sensor System” filed Jan. 20, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     The preferred embodiments of the present invention relate to an access control system for controlling access to an access point. More specifically, the preferred embodiments of the present invention relate to a method and system for controlling a token reader subsystem of an access control system in such a way as to reduce power consumption of the token reader system. 
     A wireless access control system may provide several advantages over a traditional, wire-based access control system. In a traditional, wired access control system, each access point, such as a door, for example, is equipped with a locking module to secure the access point. Each locking module is in turn directly wired to a remote access control module. The access control module is typically a database that compares a signal received from the locking module to a stored signal in the database in order to determine an access decision for that locking module. Once the access decision has been determined by the access control module, the decision is relayed to the locking module through the wired connection. 
     The use of wired connections between the access control module and the locking module necessitates a large investment of time and expense in purchasing and installing the wires. For example, for larger installations, literally miles of wires must be purchased and installed. An access control system that minimizes the time and expense of the installation would be highly desirable. 
     Additionally, wire-based systems are prone to reliability and security failures. For example, a wire may short out or be cut and the locking module connected to the access control module by the wire may no longer be under the control of the access control module. If a wire connection is cut or goes, the only alternative is to repair the faulty location (which may not be feasible) or run new wire all the way from the access control module to the locking module, thus incurring additional time and expense. Conversely, an access control system that provides several available communication channels between the locking module and the access control module so that if one communication channel is not usable, communication may proceed on one of the other communication channels, would also be highly desirable, especially if such an access control system did not add additional costs to install the additional communication channels. 
     A wireless access system providing a wireless communication channel between the locking module and the access control module may provide many benefits over the standard, wire-based access control system. Such a wireless access system is typically less expensive to install and maintain due to the minimization of wire and the necessary installation time. Additionally, such a system is typically more secure because communication between the locking module and the access control module is more robust that a single wire. 
     However, one difficulty often encountered in installing and maintaining such a wireless access system is providing power to the individual, remote locking modules. For example, many functions of the locking module may be quite demanding of power. However, maintenance costs associated with frequently changing the power sources for each of the locking modules would be highly undesirable. 
     Consequently, an access control system have increased power efficiency would be highly desirable. Such an access control system would prolong the active life of the power source, such as a battery, and would thus be highly desirable in terms of minimizing costs associated with the replacement of the power sources, such as the cost of the power sources themselves and the costs for labor to replace the power sources. 
     BRIEF SUMMARY OF THE INVENTION 
     A preferred embodiment of the present invention applies to security and identification systems, especially such systems that are responsive to the presentation of a token such as an access card or a biometric. A preferred embodiment of the present invention may be particularly useful when deployed used in conjunction with battery operated token readers. A preferred embodiment of the present invention maximizes battery life through minimizing the energy required to operate a given token reader, on demand, with minimum elapsed time. That is, a initial low-power consumption system may be continually sensing to determine whether a token has been presented. When the initial low-power consumption system detects the presence of a token, an enabling signal is sent to activate the relatively higher-power consumption token reader. Once the token has been read, the token reader is deactivated until the next time a token is detected by the initial low-power consumption system. In a typical access system, a token is presented infrequently. Consequently, significant power saving may be obtained by deactivating the higher-power consumption token reader except when necessary to read a token. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  illustrates one embodiment of the energy saving optical token presence sensor system. 
         FIG. 2  illustrates a second embodiment of the energy saving optical token presence sensor system. 
         FIG. 3  illustrates a preferred embodiment of the object presence sensor previously depicted in  FIGS. 1 and 2 . 
         FIG. 4  shows an alternative embodiment of the object presence sensor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present application may be employed in a wireless access system. Additional disclosure of such a wireless access system may be found in the following applications which are hereby incorporated by reference in their entirety: application Ser. No. 10/261,933, entitled “RF Channel Linking Method and System” filed Sep. 30, 2002; application Ser. No. 10/262,207, entitled “Energy Saving Motor-Driven Locking Subsystem” filed Sep. 30, 2002; application Ser. No. 10/262,509, entitled “Cardholder Interface for an Access Control System” filed Sep. 30, 2002; application Ser. No. 10/262,196, entitled “System Management Interface for Radio Frequency Access Control” filed Sep. 30, 2002; application Ser. No. 10/262,194, entitled “Power Management for Locking System” filed Sep. 30, 2002; application Ser. No. 10/262,507, entitled “General Access Control Features for a RF Access Control System” filed Sep. 30, 2002; application Ser. No. 10/262,077, entitled “RF Wireless Access Control for Locking System” filed Sep. 30, 2002; application Ser. No. 10/262,508, entitled “Maintenance/Trouble Signals for a RF Wireless Locking System” filed Sep. 30, 2002; and application Ser. No. 10/262,249, entitled “RF Dynamic Channel Switching Method” filed Sep. 30, 2002. 
     A preferred embodiment of the present invention applies to security and identification systems. These may represent applications where secure systems require presentation of identification tokens to obtain access to a locked space, protected space, or financial account, for example. A preferred embodiment of the present invention also applies to inventory systems where identification tokens accompany controlled assets. A preferred embodiment of the present invention has particular usefulness when deployed in battery operated token reader because it maximizes battery life through minimizing the energy required to operate a given token reader, on demand, with minimum elapsed time. Finally, a preferred embodiment of the present invention also applies to physical proximity sensors that detect when objects occupy space within the sensor&#39;s field of view. 
     Typical identification token readers, such as proximity card readers, require a relatively large amount of power to operate. Their power consumption would drain a typical battery power supply within several days or weeks. A preferred embodiment of the present invention illustrates a method and system of implementing a low average power consumption identification token reader, even though the reader transducer itself may require relatively large amounts of operating power when required to read a token. 
     The general methodology involves detection of an object&#39;s presence and using the indicium to energize the token reader immediately upon demand, in other words immediately at the onset of presentation of the token. The method and apparatus differs from prior disclosed methods that require withdrawal of the token before generation of the token present indicium. The disclosed method has several advantages including fast response time, greatly improved ambient light rejection, very low current and power consumption, hysteresis in sensing range, and low cost using commonly available electronic semiconductors. 
       FIG. 1  illustrates one embodiment of the energy saving optical token presence sensor system  100 . The optical token presence sensor system  100  includes a token reader  110 , an object presence sensor  120 , a power switch  130 , and a battery of other self-contained power supply  140 . 
     The token reader  110  resides preferably in the same housing with an object presence sensor  120  and power switch  130 . The object presence sensor  120  includes a radiation emitter  122 , a radiation sensor  124 , internal signal conditioning, and control circuitry. In a preferred embodiment, a photodiode may serve as the radiation sensor, and an infrared (IR) emitting diode (IRED) may serve as the radiation source. Also in a preferred embodiment, the IRED periodically pulses its emitted light, with a very small duty cycle, to minimize average operating power for the object presence sensor  120 . 
     At the onset of token presentation to the object presence sensor  120 , the IR light reflects from the token into the photodiode. A token may consist of an identification card, or any object that carries identifying information. For example, one&#39;s own fingerprint may embody a material token. The signal conditioning and control circuitry internal to the object presence sensor detects an increase in the photodiode&#39;s electrical signal in response to the reflected light. With a sufficient increase in this signal, the object presence sensor  120  generates a positive token present indication. The range of space adjacent to the object presence sensor for which a positive indicium of highly reflective token presence may be generated is defined as the sensor&#39;s field of view. 
     This positive indicium enables the state of the power switch  130  such that power flows from the battery  140  to the reader  110 , energizing the reader. The power switch  130  may optionally include a voltage regulator. Now that the token reader  110  has operating power, it may read data from the token, for example an inductive proximity type identification card. The apparatus preferably energizes the token reader  110  immediately upon demand. After withdrawal of the token, no reflected light reaches the photodiode, and the token present sensor indicates “no token present”, the negative token present indicium. The power switch  130  changes state to block the flow of battery power to the reader. Now only the object presence sensor  120  draws operating power from the battery  140  (or other self contained power supply). If the object presence sensor  120  design achieves sufficiently low power consumption, the apparatus may attain very long battery life. 
       FIG. 2  illustrates a second embodiment of the energy saving optical token presence sensor system  200 . The optical token presence sensor system  200  includes a token reader  210 , an object presence sensor  220 , control electronics  230 , a battery of other self-contained power supply  240 , and other sundry functions  250 . 
     The system of  FIG. 2  operated generally similar to that of  FIG. 1 , but includes control electronics sub-circuit  230  and sundry functions  250  in addition to the elements shown in  FIG. 1 . The object presence sensor  220  generates its indicium in the same way, but supplies the information to the control electronics sub-circuit  230 . 
     A preferred embodiment of the control electronics sub-circuit  230  includes a programmable microcontroller or microprocessor. Other forms of control electronics logic may also be used. Examples include discrete logic or programmable logic arrays well known to those skilled in the art. When a positive token present indicium signals a token present, the control electronics microprocessor then changes state from low power sleep mode to active mode. The microprocessor enables the supply of battery operating power to the token reader  210  and receives the read token data. The microprocessor then removes operating power from the reader  210 . 
     At any time during its wake-up state, the control electronics sub-circuit  230  may execute any number of sundry functions  250 , for example, including telemetry of RF communications to a remote authorization unit, driving motors or relays to lock or unlock access portals, activating or extinguishing audible and visible indicators, initiating other types of communications, and the like. After the transaction has completed, the control electronics  230  returns to its low current sleep mode, minimizing power consumption and maximizing battery life. 
     Use of a logical control unit such as a microprocessor in this embodiment has reliability advantages. If a non-token object such as precipitation reflects light into the object presence sensor for longer than a predetermined time, the control electronics  230  may remove operating power from the reader  210 . The control electronics  230  may discern these false indications of token present by the nonexistence of token data from the reader  210  within the predetermined elapsed time after initiation of power to the reader. An example of a predetermined elapsed time is 0.5 seconds. In this way the control electronics prevents inadvertent battery depletion using a relatively simple logic. Removal of the non-token material from the view of the sensor quite naturally preferably restores the reader to its full functionality. 
       FIG. 3  illustrates a preferred embodiment of the object presence sensor  300  previously depicted in  FIGS. 1 and 2 . The object presence sensor  300  includes a radiation emitter  310 , a radiation receiver  320 , a band-pass filter  330 , and a comparator  340 . 
     In a preferred embodiment, a photodiode may serve as the radiation sensor  320 , and an IRED may serve as the radiation source  310 . Also in a preferred embodiment, the IRED periodically pulses its emitted light, with a very small duty cycle, to minimize average operating power for the token present sensor. 
       FIG. 3  shows several sources of light incident upon the photodiode, including IRED reflections from a token, 120 Hz man made light, and nearly 0 Hz sunlight. The photodiode&#39;s electrical response to incident light flows into a band pass filter  330 . By selecting a frequency pass band that excludes 0 Hz and 120 Hz, the sensor may achieve high sensitivity even in the presence of the shown interfering light sources. Rejection of these confounding interferences prevents battery depletion due to wasteful frequent false indications of object presence. Additionally, the band-pass filter may be programmable to exclude any other type of undesired external optical signal. 
     In a preferred embodiment of the object presence sensor  300 , at least one synchronization (sync) signal coordinates the timing of the IRED driver and phase sensitive band-pass filter. Although shown as a single bus, the sync signal may take the form of a plurality of individual signals, coordinated to control the timing of events such as powering amplifiers, amplifier offset zeroing, IRED drive timing, and the like. 
     One well known characteristic of certain active phase sensitive filters translates the output to center on 0 Hz. In this case a simple comparator  340  measures the filtered photodiode response against a DC threshold level, and yields the token present indicium. If the filtered photodiode response exceeds the threshold level, then the comparator  340  yields a positive token present indicium. If the filtered photodiode response falls under the threshold level, then the comparator  340  yields a negative token present indicium. 
     It is well understood that either polarity for the comparator logic may be implemented, without material difference from the disclosed methodology. A known desirable property of comparator design includes hysteresis, a positive feedback polarity shift in the effective switching threshold of the comparator circuit. This property actually causes the token present indicium to behave in a more stable way, eliminating noise during the switching of states between present and not present, and vice versa. When an object presents itself to the object presence sensor and activates the indicium to the positive token present state, then the object must typically increase in distance from the sensor in order to reverse the indicium&#39;s state back to negative token present. This results in a clearly discernible, stable indicium for use by the sub-circuits described in these disclosures. 
     That is, instead of a single on-off threshold for detection of the token, two thresholds may be implemented. A first threshold at a higher received signal level and a second threshold at a lower received signal level. Before a token is presented, the sensor is in an “off” state. As a token is presented, the net received signal level begins to rise from zero. As the received signal level passes the second threshold, no action occurs. However, once the received signal level reaches the higher signal level of the first threshold, the sensor transitions from an “off” state to an “on” state. As the token is removed, the received signal level begins to lessen. As the received signal level passes the first threshold, no action is taken. However, once the received signal level reaches the lower signal level of the second threshold, the sensor transitions from an “on” state back to an “off” state. 
       FIG. 4  shows an alternative embodiment of the object presence sensor  400 . One skilled in the art may construct an object presence sensor of this type by using of the Motorola MC145012 integrated circuit plus sundry discrete components.  FIG. 4  has undergone simplification, compared to the MC145012 data sheet, only as necessary for clarity and relevance. One may also construct an object presence sensor of this type with a logic control unit, such as a programmable microprocessor or microcontroller, plus individual amplifiers, comparators, and so forth. 
     The object presence sensor  400  again contains the preferred IRED  410  and photodiode  420  as shown in  FIG. 4 . A laser diode or other radiation source may also embody this element, and other component choices may also embody the receiver. The sensor design again deploys the IRED and photodiode to emit and receive light respectively to and from a token target. If a photodiode is used, an optical band pass filter helps to reduce the effects of ambient interfering light. 
     The object presence sensor contains a clock and sync control sub-circuit  430  to coordinate the sensor&#39;s activities. This block in actuality may be distributed within the sensor. The clock preferably is able to control the timing of the IRED light pulse width, the IRED pulse frequency, the IRED pulse initiation time within the overall chain of events, the power up time of the amplifier, the zeroing of the amplifier offset, the reference voltage for the photodiode bias, and the comparator. With respect to the comparator, for example, multiple positive logic inputs may be required prerequisite to generation of a positive token present indicium. A preferred IREDpulse width of about 100 microseconds or less may be chosen. 
     R1 may preferably allow approximately 5 milliamperes to flow through an IR LED light source. A different current may be required if a different radiation source is chosen. 
     The period of IRED pulsation may preferably come to about 150 milliseconds or less, in order to achieve acceptable immediacy of sensor response. If the majority of the average current draw occurs in the IRED drive, then the approximate current consumption comes to: 5 mA×100 microseconds/150 milliseconds=3.3 microamperes average. This makes for a very acceptable number with respect to long battery life. In actuality, the other blocks in the object presence sensor may draw significant amounts of current, such that a total average current draw of 20 to 25 microamperes may be expected. Still, this operating current provides years of battery life if sufficient batteries are chosen, such as multiple AA type alkaline batteries. 
     Radiation reflected from the identification token into the photodiode generates a current indicated by the arrow, and labeled “i”. R3, preferably approximately 47 kilo-ohms, converts the photodiode current into a voltage. The sync control allows for several desirable events to take place: 
     The sync control turns on the Vref voltage and the amplifier. 
     The amplifier settles to a stable state before subsequent events. 
     The sync control closes the offset null switch to zero the amplifier output. 
     The sync control then opens the switch to allow amplification of subsequent photodiode signals. 
     The sync control then triggers the IRED pulse. 
     The amplifier amplifies changes in the photodiode signal. 
     This synchronized timing scheme reduces the effects of interfering ambient light whose effective periodicity is much greater than 100 microseconds. The desirable effect has similarity to phase sensitive active band pass filtration depicted in  FIG. 3 . 
     The amplifier has a capacitive pulse amplification topology whose pulse gain comes to approximately −(Ci/Cf). The design preferably employs Ci&gt;Cf for voltage gain. Other capacitive amplification topologies are possible, including an integrating topology. A low noise integrating topology would result by substituting a short circuit for Ci, yet the same zeroing functionality may be obtained. 
     The comparator yields the token present indicium using a comparison with a threshold reference. The comparator may contain hysteresis and also require a multiplicity of positive logic inputs prerequisite to generation of a logical token present positive indication. 
     While particular elements, embodiments and applications of the present invention have been shown and described, it is understood that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teaching. It is therefore contemplated by the appended claims to cover such modifications and incorporate those features that come within the spirit and scope of the invention.