Description

This disclosure relates to access control systems.

In areas secured by an access control system, users are often required to present some form of credential before being allowed to pass through a door or other barrier. For example, a user may need to use one or more of a key (mechanical or electronic), a code, a biometric feature or other device to obtain access.

US 2011/0048862 A2 describes an elevator system in a building. When movement of a door in the building is detected (e.g., movement of an apartment door as it is being closed or opened), an elevator car is sent to the floor where the door is located. The elevator doors open at the floor after a passenger-specific route time has expired.

Further options for access control could be advantageous. This is addressed by at least some of the embodiments covered by the claims.

An access control system detects movement at a door to which a user has been granted access based on a credential presented by the user. A travel time is determined that describes how long the user is expected to need to travel between that door and another door in the area. After the travel time has elapsed, the other door is unlocked, wherein access for the second door is being granted without the user presenting the credential for the second door. Thus, the user can travel to and open the other door without having to present the credential for the other door.

Some embodiments of an access control method comprise: identifying a user based on a credential presented by the user; granting the user access for a first door based on the credential; detecting a movement at the first door; adaptively determining a travel time for the user between the first door and a second door; and granting the user access for the second door after the travel time for the user between the first door and the second door has elapsed since the movement at the first door, wherein access for the second door is being granted without the user presenting the credential for the second door. The adaptively determining a travel time for the user can comprise adjusting a parameter over time based on feedback from a sensor for the first door or the second door. The adaptive- ly determining a travel time for the user can comprise recording a user travel time during a setup period of an access control system. In some cases, the adaptively determining a travel time for the user can further comprise replacing the recorded user travel time with a new travel time, the new travel time having been determined after the setup period of the access control system. In other cases, the adaptively determining a travel time for the user can further comprise calculating a distance between the first and second doors based on the at least one user travel time. The adaptively determining a travel time for the user can also comprise determining the travel time based on a plurality of previous walk speeds. The determining the travel time based on a plurality of previous walk speeds can comprise averaging a plurality of travel times for the user. In some cases, at least one of the previous walk speeds is for a travel path other than between the first and second doors. In particular embodiments, the adaptively determining a travel time for the user comprises determining an individual walk speed for the user. The travel time for the user can also be based on additional environmental information for an area. The additional environmental information can comprise one or more of temporal information, traffic information, and group information. The additional environmental information can comprise walk speeds of one or more other users.

Additional embodiments of the method further comprise: detecting a movement at the second door; adaptively determining a travel time for the user between the second door and a third door; and unlocking the third door for the user after the travel time for the user between the second door and the third door has elapsed since the movement at the second door.

Embodiments of a building access control system can comprise: a first door; a door sensor for the first door ; an input device for the first door; a second door, the second door not being an elevator door; and a computer-based control unit, the control unit comprising a processor and a computer-readable storage medium with instructions that, when executed by the processor, cause the control unit to identify a user based on a credential presented by the user, grant the user access for the first door based on the credential, detect a movement at the first door, adaptively determine a travel time for the user between the first door and a second door, and grant the user access for the second door after the travel time for the user between the first door and the second door has elapsed since the movement at the first door, wherein access for the second door is being granted without the user presenting the credential for the second door. Further embodiments comprise a computer-based device configured to perform one or more of the disclosed methods.

At least some embodiments of the disclosed methods can be implemented using a computer or computer-based device that performs one or more method acts, the computer or computer-based device having read instructions for performing the method acts from one or more computer-readable storage media. The computer-readable storage media can comprise, for example, one or more of optical disks, volatile memory components (such as DRAM or SRAM), or nonvolatile memory components (such as hard drives, Flash RAM or ROM). The computer-readable storage media do not cover pure transitory sig- nals. The methods disclosed herein are not performed solely in the human mind.

The disclosure refers to the following figures, in which:

FIG. 1 shows a plan view of an exemplary embodiment of a building floor.

FIG. 2 shows a block diagram of an exemplary embodiment of an access control system. FIG. 3 shows a block diagram of an exemplary embodiment of an access control method.

FIG. 4 shows an exemplary embodiment of a distance table.

FIG. 5 shows a plan view of an exemplary embodiment of a building floor.

FIG. 6 shows a signal diagram for an exemplary exchange of signals in an access control system.

FIG. 7 shows a block diagram of an exemplary embodiment of a computer.

FIG. 1 shows a plan view of an exemplary embodiment of a building floor 100 in which various embodiments of the disclosed technologies can be used. The floor 100 comprises a lobby 102, which is accessible from outside of the building by an exterior door 110. Interior doors 120, 122, 124 allow access to rooms A, B, and C, respectively. In this particular example, the lobby 102 is also served by two elevators 130, 132. In further embodiments, doors that control access to other areas (e.g., stairwells, garages, storage spaces, outdoor spaces) are present. As used in this application and in the claims, a "door" refers generally to a barrier that is used to control access to an area. Thus, in addition to planar elements that slide or that rotate on hinges, a door can also include barriers such as a gate or a turnstile. Such barriers can be physical (e.g., a bar or other object) or sensor-based (e.g., an optical sensor, a motion sensor, or another sensor). In some cases, a door is an elevator door. The phrase "building door" refers to a door that is not an elevator door, but can include an exterior door, an interior door, an office door, a turnstile, or another type of barrier.

FIG. 2 shows a block diagram of an exemplary embodiment of an access control system 200. The system 200 comprises a computer-based control unit 202. The control unit 202 comprises at least one processor and at least one computer-readable storage medium, which stores instructions for the processor. When the processor executes the instructions, the control unit 202 performs one or more of the method acts disclosed herein. The control unit 202 is communicatively coupled to additional components through a network 204. The control unit 202 is coupled to a door 210 and to a door 212. The doors 210, 212 can comprise respective door sensors 220, 222. The door sensors 220, 222 detect movement at the respective door. This detecting can comprise detecting the movement of the user at or near the door. This movement of the user can result from the user passing through the door. This detecting can also comprise detecting movement of the door 210, 212. For example, the sensors 220, 222 can detect if the door is being opened, being closed, or both. Generally, the sensors 220, 222 can comprise motion sensors, optical sensors, pressure sensors, camera sensors, or other sensors.

One or both of the doors 210, 212 can further comprise respective actuators 230, 232, which can operate in response to an electronic signal. For example, in some embodiments, the actuator 230 can lock or unlock a lock for the door 210. In further embodi- ments, the actuator 230 can open or close the door 210.

The system 210 can also include additional doors.

Also coupled to the control unit 202 is an input device 240 for the door 210. The input device 240 obtains credential information for a user and provides this information to the control unit 202. Generally, credential information allows for distinguishing a user from one or more other users, and examples of credential information are given below. The credential information can be provided by the user with a data carrier 244, for example, one or more of: an RFID (radio-frequency identification) device (e.g., having a card form factor or other form factor), including near-field communication (NFC) devices and far- field communication devices; magnetic storage devices (e.g., magnetic strip cards); or optical code devices. Accordingly, the input device can comprise an RFID reader, an NFC reader, a magnetic reader, an optical scanner, or another type of reader. In additional embodiments, the credential information is provided by the user through a keypad or a biometric reader. In FIG. 2, an input device 242 is also provided for the door 212.

The control unit 202 is also coupled to a database 250. The database 250 stores information that describes, for example, access rights for one or more users. The database 250 can also store "automatic destinations" for one or more users. An automatic destination is an indication of a door through which a user is expected to pass after passing through a previous door. The database 250 can also store additional information, as described herein.

In further embodiments, the control unit 202 is also coupled to a computer-based elevator control unit 260. The elevator control unit 260 can control one or more aspects of an elevator system in a building (though some embodiments can be used in settings where no elevator installation is present).

The control unit 202 can also be coupled to one or more other components 270. For example, the other component 270 can be a remote monitoring system. In some cases, the components of the system 200 are located locally, while in other cases, at least some components are remotely located from each other (e.g., the components form a distributed system).

FIG. 3 shows a block diagram of an exemplary embodiment of an access control method 300. At least a portion of the method 300 can be performed using, for example, a com- ponent such as the control unit 202. Although the method 300 is described herein as being performed in the context of a system such as the system 200 of FIG. 2, it can also be used with other systems.

In a method act 310, a user is identified. This identification is made based on credential information provided to the control unit 202, possibly through an input device 240, 242. Generally, a user is "identified" when the access control system is able to distinguish the user from one or more other users or groups of users. Depending on the embodiment, the credential information comprises, for example, one or more of a name for the user, a number, a biometric feature, or another type of information.

In a method act 320, movement at a first door is detected. The first door is one to which the passenger has access (perhaps as a result of providing the credential information), and the movement is assumed to result from the identified user passing through the door. The movement is detected using one or more sensors, for example, the door sensor 220, 222.

In a method act 330, a travel time for the user is determined. The travel time describes the approximate amount of time that the user is expected to take to travel from the first door to a second door. For example, in the context of the building floor 100 of FIG. 1 , the access control system determines a travel time for the user to travel from the exterior door 110 to the interior door 124. The second door is determined based on an automatic destination for the user.

In a method act 340, the access control system determines that the travel time has elapsed since the detecting of the movement at the first door. By this point, the user is expected to be at or near the second door.

In a method act 350, the second door is unlocked. This can be performed using, for example, a command sent to an actuator 230, 232 of the second door. The second door can then be opened by the user. A door is "unlocked" when an impediment to the user passing through the door is physically or electronically removed. For a door with a mechani- cal lock, this could mean, for example, that a deadbolt is opened. For some doors, this could mean that an electronic alarm is deactivated. A door is "locked" or "relocked" when the corresponding impediment for the door is physically or electronically activated.

Particular embodiments of the method 300 comprise an additional method act 360, in which the second door is re-locked after the access control system determines that the second door has not been opened within a certain amount of time. This determination can be based on data from a sensor for the second door. This time limit can be, for example, 10 seconds, 20 seconds, 30 seconds, 60 seconds, 2 minutes, 5 minutes or another amount of time. In some cases, the time limit can be set by a user or by a system administrator. This feature can help prevent an unauthorized party from opening the second door after it has been unlocked. For example, the second door can be unlocked for a user, but the user may be delayed from reaching the second door. Since the user is not present to open the second door, the door is re-locked after an additional amount of time has passed.

In some cases, the second door is unlocked such that the unlocking is not apparent to anyone who happens to be near the second door at the time. For example, the unlocking is not indicated by any audio or visual indicators on or near the second door. This can improve the security of the access control system, since otherwise an unauthorized person may notice that the second door is unlocked and then open the door.

Various methods can be used to determine the travel time for a given user and a given pair of doors.

In some embodiments, the distance between the first and second doors is retrieved from a table stored in the database 250. FIG. 4 shows an exemplary embodiment of a distance table 400. In this particular example, the distance table 400 describes distances between various doors of the floor 100 of FIG. 1. For example, table 400 shows that: the path 150 between the exterior door 110 and the interior door 124 has a length of 10 meters; the path 152 between the elevator 130 and the interior door 122 has a length of 9 meters; and the path 154 between the interior door 120 and the interior door 122 has a length of 5 meters. Of course, the size of the table 400 and the actual values stored therein vary according to the particular embodiment.

In some cases, the distances between two doors are calculated based on a coordinate system describing the locations of the doors in an area and based on a path that the user is expected to take between the doors. The paths 150, 152, 154 are shown in FIG. 1 as comprising straight lines with 90-degree turns, but the paths can also be modeled with curved lines, which may better represent the actual paths that users walk between doors.

Once the appropriate distance has been retrieved, a user's individual walking speed can be retrieved from another table stored in the database 250. The individual walking speed is manually added to the database previously. In some cases, the individual walking speed can be modified by one or more of the user, an administrator, or another party.

The access control system calculates the travel time based on the distance between the first and second doors and the user's individual walking speed.

In other embodiments, the travel time for a given user and a given pair of doors is manu- ally programmed into a list in the database 250. In further embodiments, the travel time for a given user and a given pair of doors is determined using one or more adaptive methods. As used herein, an "adaptive" method is a method that adjusts one or more parameters over time based on feedback received by the access control system. A first embodiment of an adaptive method determines the distance between two doors based on a pre-defined walk speed. First, the amount of time that a user takes to travel between two particular doors is measured. This measurement can be performed during, for example, a "commissioning" or "setup" period. This measured time is multiplied by the pre-defined walk speed to obtain the distance between the two doors. The distance can be stored in, for example, a distance table in a database. Later, when the access control system expects a user to travel between those particular doors, the corresponding travel time can be determined. For example, the stored distance between the doors can be retrieved from the database and divided by the pre-determined walk speed. Of course, since the distance between the doors is related to the travel time by the pre-determined walk speed, the values stored in the database can be any of distance values, travel time values, and a value derived from the distance value or the travel time value.

Later, new travel times or distances can be measured and stored for use in place of the previous travel times or distances. In different variations of this embodiment, the new travel times or distances can be compared with or statistically combined with the previous travel times or distances. For example, a distance between two doors can be computed (or re-computed) using the average of a previous travel time and a new travel time. This can be repeated using measurements of multiple users. In further variations of this embodiment, outlying measured values (e.g., very large or very small values) are disregarded. Of course, the act of re-computing the distance between two doors does not necessarily signify that the physical arrangement of the doors has changed since a previous computation (though that might be the case). Instead, the newly calculated distance may reflect characteristics of one or more users, such as the actual paths taken by the users or the actual walk speeds of the users. In a non-limiting example of this first embodiment, a commissioning period is conducted for an access control system. During this commissioning period, the time that a user (e.g., a test user) takes to walk from an exterior building door to an interior building door is measured. The measured time is 5 seconds. Based on a pre- determined walk speed for the user of 1.4 meters per second, the distance between the two doors is calculated to be 7 meters. (In this example, the pre- determined walk speed is a "generic" speed used for initially configuring the access control system.) This distance and the measured time are stored in a database of the access control system. After the commissioning period is finished and the access control system is in normal operation, another user passes through the exterior door towards the interior door. For this user, the control system determines a travel time by reading the stored distance from the database and dividing the distance by the pre-defined walk speed. Thus, for this user, the control system uses a travel time that is the same as the time measured during the commissioning period. However, this user actually needs a longer time to travel between the two doors, a fact which the control system recognizes when the user is detected as actually opening the second door. The longer time is a result of a particular path that the user chooses to take between the doors. Based on the user's actual travel time, the control system calculates a new distance and stores this new distance in the database. The next time that this user travels between the same two doors, the new distance is used to determine the travel time for the user. Thus, the access control system learns to respond more appropriately to this particular user.

A second embodiment of an adaptive method determines individual walk speeds of particular users. Initially, a user's stored, individual walk speed may be a default value or a custom, manually set value. During operation, a given user's walk speed can be calculated based on predefined distance values between two doors. The user's walk speed can also be based on adaptively determined distance values between two doors. In any case, the distance values can be retrieved from a database. The access control system then calculates the new individual walk speed by dividing the distance between the doors by a measured travel time. The newly calculated individual walk speed can later be used in place of the previous individual walk speed (e.g., in place of the default value). Alternatively, two or more walk speeds (e.g., an older walk speed and a newer walk speed) can be averaged to produce an average individual walk speed. This value is stored by the control system and applied later, when the user moves between the same two doors or between other combinations of doors. The individual walk speed can be stored in the database of the access control system.

In further variations of this embodiment, outlying measured values (e.g., very large or very small values) are disregarded. In some variations of this embodiment, an individual walk speed for a particular user can be set as a fixed value that is not changed, regardless of a measured walk speed. In additional variations, a user's walk speed can have an upper limit, a lower limit, or both. In some cases, a manually defined offset is added or subtracted from a learned walk time. In a non- limiting example of this second embodiment of an adaptive method, a user passes through an exterior door and moves toward an interior door. In determining the travel time for this user, the access control system reads the user's individual walk speed and the distance between the two doors from a database. The system then calculates the corresponding travel time. When the user passes through the second door, its door sensor sends a signal to the access control system. The system thus determines that the user arrived at the second door 5 seconds later than expected, and thus the actual individual walk speed was slower than the individual walk speed retrieved from the database. The system averages these two walk speeds to create a newly calculated walk speed, which is then stored in the data base for future use. A third embodiment of an adaptive method uses stored travel-time values in conjunction with additional environmental information. The additional environmental information can include one or more of any of the following: temporal information (e.g., the time of day, the day of the week); traffic information (e.g., the number of users traveling between the same doors at about the same time, the number of users traveling at a similar time in a similar part of the building); group information (e.g., walk speeds of one or more other users traveling at about the same time); and other information. The additional information can allow the access control system to determine a travel time that is appropriate for a given time, a given traffic situation, a given travel path, or a given group of users. For example, a travel time over a given path could be determined based on measurements taken only for users traveling along that same path. As another example, a travel time for a given time of day or day of the week can be determined based on previous measurements for that time or day. As another example, an expected walk speed for a user can be limited to the walk speed of other users on that path at that time. Thus, the use of the additional information can help account for factors that can affect how quickly a user moves between two doors. For example, a user may move more slowly through a hallway if there are many other people there, especially if those other people are moving in a different direction than the user. As another example, a user may move more slowly going up a staircase than walking across a level floor. As a further example, a healthy person may move more slowly if walking behind or in the company of a person in a wheelchair.

In some cases, the additional information is evaluated using one or more statistical methods. For example, the statistical methods may: calculate average values; calculate median values; use quantiles to limit calculated values; or weight values depending on different factors (e.g., how recent the values are, or how similar an actual path's distance or location in a building is compared to the distance or location of a path for which a previous value was recorded).

In some cases, determining travel times using an adaptive method can be simpler than using a non-adaptive method (e.g., the method described above that uses the distance table 400, or the method described above that uses a manually programmed list). Adaptive methods do not necessarily require a coordinate system that describes the locations of the doors. Thus, the effort of defining the position of every door in a coordinate system, or adjusting the individual walk speed, or both, can be avoided. Generally, adaptive methods like those described herein can help an access control system to automatically adapt to changes in a building layout. Such changes may arise, for example, when barriers created by remodeling or other events create detours that alter travel times between doors. Adaptive methods can also allow the access control system to adjust to personal characteristics of a user (e.g., walk speed of a user), including as those characteristics change over time. For example, a user's walk speed may change with the user's health or age. Adaptive methods can also combine information about multiple users in an area, and then adjust travel times according to how crowded the area is, or according to the presence of slower users. Compared with methods that use only manually defined or static values, adaptive methods can allow an access control system to more accurately determine values for distances between doors or walk speeds of users, or both. This is because, for example, multiple actual measurements are used.

Some embodiments of the disclosed technologies can be used with an elevator system. As shown in FIG. 2, the control unit 202 can be coupled to an elevator control unit 260. In such cases, the elevator doors (e.g., the elevator hall doors or the car doors) can serve as the first door in the method 300. After the elevator doors open at the destination floor and the travel time has elapsed, then the second door is unlocked. In some cases, the second door is for an office or apartment of the user. The user can be identified before boarding the elevator to travel to the destination floor where the second door is located. For example, in cases where the elevator system uses destination call control technology (such as Schindler ID or PORT from the Schindler Group of Switzerland), the user can be identified as part of placing a destination call for the elevator. The destination call can be placed using any type of credential described herein.

In further embodiments, the elevator doors (e.g., the elevator hall doors or the car doors) can serve as the second door in the method 300.

In particular embodiments, two or more doors are unlocked successively after a user is identified and after movement at a first door is detected. FIG. 5 shows an exemplary embodiment of a building floor 500 where such embodiments can be used. In FIG. 5, an exterior door 510 opens into a lobby 502, where an interior door 526 opens into a second lobby 504. From the lobby 504, interior doors 522, 524 open into rooms Y and Z, respectively. Elevators 530, 532 are also accessible from the lobby 502.

When a user is identified and movement at a first door (e.g., the exterior door 510) is detected, then a travel time for the user between the first and second doors is determined. In this particular example, the second door is the interior door 526, and the user is generally traveling along the path 550. (Of course, these details are only non-limiting examples.) After the determined travel time between the first and second doors has elapsed, the second door (interior door 526) is unlocked. A travel time for the user between the second door and a third door (here, interior door 524) is also determined. Once the movement at the second door is detected, and after the travel time between the second and third doors has elapsed, the third door is unlocked for opening by the user. Thus, the user can use a credential to gain access to a first door and then pass through multiple additional doors without having to present the credential again. If the access control system unlocks the second door, for example, but does not detect the second door as being opened within a time limit, then any further doors that the user was expected to pass through (e.g., the third door) are not unlocked. This may be relevant in situations where, for example, the user is delayed before opening the second door, or where the user simply takes a different path through the floor 500 than expected by the access control system.

Although not shown in FIG. 2 or FIG. 5, at least some of the doors have readers for ob- taining credential information (e.g., for reading RFID cards or other credentials). In some cases, each door has its own reader.

FIG. 6 shows a signal diagram for an exemplary exchange of signals in an access control system using one or more embodiments of the disclosed technologies. For ease of refer- ence, the signal diagram is described in the context of the system 200 of FIG. 2 and of the method 300 of FIG. 3, but other systems and methods can also be used.

During the signal exchange, an input device 240 receives credential information and sends the information to the access system control unit 202 in a signal 610. The control unit 202 verifies that the user associated with the credential information is authorized to pass through a first door (e.g., the door 210), and the control unit 202 then sends an unlock signal 620 to the first door (e.g., to the actuator 230). Once movement at the first door is detected, indicating that the user is passing through the first door, a movement signal 630 is sent from the first door to the control unit 202. The movement signal 630 is generated by the door sensor 220. The control unit 202 then waits for the user's travel time to elapse, after which it sends an unlock signal 640 to a second door (e.g., the door 212). The unlock signal 640 is sent to, for example, the actuator 232. Once the user opens the unlocked second door, the second door sends a movement signal 650 to the control unit 202. The movement signal 650 is generated by the door sensor 222 and confirms to the central control unit that the second door was opened. FIG. 7 shows a block diagram of an exemplary embodiment of a computer 700 (e.g., part of an access control system control unit, part of an elevator control unit, part of a reader, part of a database) that can be used with one or more technologies disclosed herein. The computer 700 comprises one or more processors 710. The processor 710 is coupled to a memory 720, which comprises one or more computer-readable storage media storing software instructions 730. When executed by the processor 710, the software instructions 730 cause the processor 710 to perform one or more of the method acts disclosed herein. Further embodiments of the computer 700 can comprise one or more additional components. The computer 700 can be connected to one or more other computers or electronic devices through an input/output component (not shown). In at least some embodiments, the computer 700 can connect to other computers or electronic devices through a network 740. In particular embodiments, the computer 700 works with one or more other computers, which are located locally, remotely, or both. One or more of the disclosed methods can thus be performed using a distributed computing system. At least some of the disclosed embodiments can allow a user to pass through multiple doors without having to present a credential to open each door. Instead, the user only needs to present the credential before passing through the first door. One or more successive doors are unlocked automatically after the appropriate travel time has elapsed. Wait- ing for the elapse of the travel time can also help ensure that a door is not unlocked too early (e.g., before the user arrives at the door to open it). This can reduce the risk that an unauthorized person will open the unlocked door instead of the user. Additionally, not having to unlock every door manually can be helpful to, for example, users whose hands are full (e.g., carrying shopping bags or other objects) or who are disabled. The disclosed technologies can also provide a user with a feeling of personal attention while passing through the building or other area.

In one non-limiting example, a user approaches an exterior building door. The user presents an electronic key (an RFID card) to a reader that is positioned near the exterior door. The reader reads credential information from the card (in this case, an identifica- tion number associated with the user) and sends this information to an access control system control unit. The control unit determines that the user is authorized to use the exterior door, and so the control unit unlocks the exterior door. After detecting that the user has opened the exterior door, the control unit determines a travel time for the user to move from the exterior door to an office door. During this time, the user is walking from the exterior door to the office door. After the travel time has elapsed, the control unit unlocks the office door. At about the same time, the user arrives at the office door and opens the door.

In another non-limiting example, a user travels in an elevator car to a floor where the user's apartment is located. Before boarding the elevator, the user placed a destination call using an RFID card. As a result, the elevator system and the access control system have identified the user. The access control system has also determined that the travel time for the user from the door of the elevator on the destination floor to the apartment door is fifteen seconds. Once the elevator car arrives at the floor where the apartment is located, the elevator hall doors open. This door movement is communicated to the access control system. Meanwhile, the user exits the elevator and walks toward the apartment door. After the fifteen-second travel time has elapsed, the access control system unlocks the apartment door. However, the user is not at the apartment door at this point, since the user stopped in the hallway to speak with a neighbor. The access control system provides a thirty-second window for the user to open the unlocked apartment door. When this window lapses without the access control system having received an indication that the apartment door was opened, the apartment door is re-locked. Later, the user unlocks the apartment door using the RFID card and opens the door. Although certain data are described herein as being stored in a table, a list, or in another data structure, generally such data can be stored in any suitable type of data structure. This applies to, for example, individual walking speed data and data for distances between doors.

Although some embodiments of the various methods disclosed herein are described as comprising a certain number of method acts, further embodiments of a given method can comprise more or fewer method acts than are explicitly disclosed herein. In additional embodiments, method acts are performed in an order other than as disclosed herein. In some cases, two or more method acts can be combined into one method act. In some cases, one method act can be divided into two or more method acts. As used herein, a "user" can be a person, a group of persons, a machine, or an animal.

Having illustrated and described the principles of the disclosed technologies, it will be apparent to those skilled in the art that the disclosed embodiments can be modified in arrangement and detail without departing from such principles. In view of the many possible embodiments to which the principles of the disclosed technologies can be applied, it should be recognized that the illustrated embodiments are only examples of the technologies and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims and their equivalents. I therefore claim as my invention all that comes within the scope of these claims.