The present invention relates to systems and methods for controlling
The invention relates generally to the sensing of unauthorized passage
of objects, as well as people through the doors, especially "piggybacking".
Security doors are used in airports, banks, commercial buildings,
military installations, and other locations where restricted access is desirable.
One type of security door is a revolving door such as disclosed in US Patent No
4,627,193. Normally, in this type of door, a person inserts a pass card, then enters
a compartment on one side of the door. If the card is authorized, the door will
turn until the entered compartment moves from the entrance to the exit. As the
entered compartment revolves, all compartments move by a corresponding amount.
Therefore, it is possible for an unauthorized person to "tailgate", ie, to either
enter the compartment immediately following the one containing the authorized
person, or enter a compartment located at the exit. It is also possible for two
people to attempt to pass in the same compartment ("piggybacking").
One way that tailgating and piggybacking have been detected is by
the use of floor mats in the security door to detect when a compartment has been
entered. However, such mats have several drawbacks.
US Patent No 4,628,496 discloses the use of ultrasonic sensors, instead
of mats, but use of such sensors in a revolving door present difficult problems.
First, the sensors must distinguish between door panels and people or objects.
Because the sensors are merely turned off when the door panel passes by, objects
attached to, or close to, the door panel can get through the doorway undetected.
Second, to detect small objects, such as pass cards or firearms, the sensors must
have a high gain. Such a high gain increases the likelihood that reverberations
or echoes will cause false readings. This is especially true in a security revolving
door which has a substantially closed housing. Similarly, the greater the range
(portion of the floor to ceiling distance) covered by the sensor, the greater the
likelihood of false readings due primarily to echoes from the floor.
Piggybacking is detected by checking the passage of the number of persons past
a given number of ultrasonic sensors.
It is an object of the present invention to provide an improved system
and method for controlling a security door.
According to the present invention there is provided a control system
for a security door having a housing with a first portal, a second portal, and
movable door means, forming at least one compartment, for normally blocking passage
between the first and second portals, the control system comprising: means for
identifying an authorized user; means for moving the door means to move a compartment
containing the authorized user from the first portal to the second portal; means
for tracking movement of the door means and the compartment containing the authorized
user from the first portal to the second portal; sensing means disposed in the
housing for emitting energy waves into the housing between the first and second
portals, and for detecting echoes of the energy waves due to any objects or users
in the housing; and a controller connected to the means for moving, the means for
identifying, the means for tracking and the sensing means for driving the means
for moving in response to identification of an authorized user, and for determining
that there is a second user in the compartment containing the authorized user
in response to echoes detected by the sensing means, characterized in that the
controller includes means for determining a height of an object or user detected
by the sensing means and responsive to successive detected heights complying with
a height related criteria to determine that there is a second user in the compartment
containing the authorized user.
According to the present invention there is further provided a method
for controlling a security door of a type having a housing with a first portal,
a second portal, and a movable door means, forming at least one compartment, for
normally blocking passage between the first and second portals, the method comprising
the steps of: identifying an authorized user; moving the movable door means to
move a compartment containing the authorized user from the first portal to the
second portal in response to identification of an authorized user; keeping track
of the amount of movement of the door means; emitting bursts of energy waves from
sensing means into the housing between the first and second portals, and detecting
echoes of the energy waves with the sensing means due to any objects or users in
the housing; and determining that there is a second user in the compartment containing
the authorized user in response to echoes detected by the sensing means and the
amount of movement of the door means, characterized in that the determining step
comprises determining successive heights of an object or user in the compartment
and using the detected heights to determine when the compartment contains an unauthorized
A system and method of controlling a security door and embodying
the invention, will now be described, by way of example, with reference to the
accompanying diagrammatic drawings, in which:
Brief Description of the Drawings
Detailed Description of the Preferred Embodiment
- FIG. 1 is a perspective view of a security door incorporating sensors and a
control scheme according to the present invention;
- FIG. 2 is a view of the underside of the top of the security door of FIG. 1
to illustrate placement of the sensors;
- FIG. 3 is a schematic showing major components of the security door control
- FIGS. 4A and 4B are waveform diagrams of the energy waves emitted by, and reflected
toward, the sensor;
- FIG. 4C is a waveform diagram of energy waves emitted by the sensor;
- FIG. 5 is a schematic of the memory used in the control system according to
- FIG. 5A is a further schematic of the memory of FIG. 5; and
- FIG. 6 is a flowchart showing the inventive control scheme.
The control and sensor system for a security door according to the
invention operate together to detect the presence of unauthorized persons (or objects)
attempting to gain passage through the door by "piggybacking", as well as "tailgating."
When piggybacking or tailgating is detected, the control system will prevent the
unauthorized person or people from passing through by stopping the door. In a
preferred embodiment, the door will then be reversed to forcibly move the unauthorized
user(s) to the entrance or exit at which he (they) entered the door.
FIG. 1 shows a security door 20 with sensors and a control system
according to the present invention. Preferably, door 20 is a revolving door. The
door is incorporated into a wall 22 which separates a security area 24 from a
general access, or lesser, security area 26. The wall 22 with door 20 functions
as a security barrier between areas 24 and 26.
The door has a cylindrical housing 28 which includes upstanding,
semi-cylindrical panels 30. The panels 30, as shown in FIGS. 1 and 2, extend between
a circular bottom 32 and a top 42. The panels preferably span approximately 90°
of arc. Each panel 30 is fashioned from a pair of semi-cylindrical segments (such
as glass) connected between, and supported by, edge posts 36, a center post 38,
and a bottom skirt 40 secured to the bottom 32. The posts 38 are connected to
the wall 22 to incorporate the panels 30 into the wall structure. The semi-cylindrical
segments may be fashioned from various materials, including standard or safety
glass, bullet-proof glass, acrylic, or solid bars, as desired.
The top 42 is typically incorporated into the ceiling (not shown)
of the facility. The panels 30, top 42, and bottom 32 cooperate to define cylindrical
housing 28, having two arcuate portals, an entrance 44 in general access area
26, and an exit 46 in security area 24.
To prevent unauthorized persons from passing between the entrance
44 to exit 46, door 20 includes a revolving door member 48 disposed in the housing
(see FIG. 2). Revolving door member 48 has a rotatable shaft 50 supported between
the top 42 and bottom 32. The top 42 has an axial opening (not shown) through
which shaft 50 protrudes. Four wings 52 project outwardly from shaft 50 and are
of sufficient length to sweep close to semi-cylindrical panels 30. While door
20 preferably has four identical panels or wings 52 spaced roughly 90° from one
another, more or fewer panels with other spacing could be used, as desired. The
four spaced panels 52 cooperate with housing 28 to define four rotatable pie-slice-shaped
compartments. A person desiring to move from one of the areas 24, 26 to the other
enters a selected compartment and travels therewith between entrance 44 and exit
Door 20 has a drive system 60 which includes an electric motor, a
motor multiplier, and a gear reducer, such as described in U.S. Patent No. 4,627,193,
hereby incorporated by reference. Drive system 60 is coupled to revolving door
member 48 so that operation of the drive system rotates member 48.
The door wings 52 each include a rectangular frame 70 supporting
a pane 72. The frame 70 has a length to project from the shaft 50 to sweep closely
to the semi-cylindrical panels 30 as the member 48 revolves and it has a height
to extend from a location near the bottom 32 to a position near the top 42.
To prevent unauthorized ingress and egress from security area 24,
a control system is provided. In the disclosed embodiment, the control system is
located in a box 94 on the top 42 of housing 28. While the following description
is (for purposes of explanation) primarily directed toward unauthorized entry into
security area 24, the description is equally applicable to the situation where
unauthorized items, including personnel, attempt to exit the security area.
As shown in FIG. 3, the inventive control system includes a main
processor 194, a security controller 294, and supporting peripheral hardware housed
within enclosure 94 for controlling the starting, stopping, and directional rotation
of the motor and shaft which turn the compartments. As a specific example of the
preferred embodiment, the main processor is an Intel 8749 or 8751 microprocessor
manufactured by Intel Corporation, and the controller is a Zilog Z8 microprocessor
manufactured by Zilog Corporation. The peripheral hardware includes a memory 394,
sufficiently large to perform calculations and control functions which will hereinafter
become apparent, for example, a random-access memory (RAM). Suitable types and
sizes of memory will be evident to one of ordinary skill and will depend upon
the desired speed and accuracy of the detection system and the various memory management
The main processor 194 includes, or is linked to, a mechanism which
determines door position, e.g., by using a pulse generator as set forth in U.S.
Patent No. 4,627,193. In that patent, door position is tracked by using a cam
and a cam follower, which has its motion translated by a proximity sensor into
pulses which occur at each predetermined increment of door rotation, e.g., 3°.
This mechanism is represented in FIG. 3 by position detection system 197. The pulses
are recorded by a counter, which is read by main processor 194. The value on the
counter corresponds to a specific amount of door rotation. The position indicator
also preferably gives a second signal indicating each 90° of rotation. These pulses
may be given directly to the security controller 294, too. When the door completes
180° of rotation, i.e., the point in the present embodiment where the entered
compartment has moved to the exit compartment, another proximity detector in detection
system 197 indicates such movement to main processor 194, and the processor stops
drive system 60 and resets the counter. The control system also includes identification
devices 110, 114, such as card readers or other devices for identifying an authorized
user, to initiate the entry sequence and anti-jam features, as set forth in that
In the present invention, to detect people or objects, the door includes
an array of sensors 99a-99h, preferably arranged in a circular pattern around the
ceiling of the housing, as depicted in FIG. 2. It is preferred to mount the sensors
on the ceiling, rather than the floor where they may be stepped on or subjected
to rain, water, snow, dirt, or other undesirable environmental conditions.
The sensors radiate energy waves, preferably ultrasonic, in a generally
conical shape and detect the echoes of the waves reflected from any physical surfaces
encountered. Having multiple concentric arrays of the sensors around center post-axis
24 allows greater coverage of the area in the compartment. Preferably, each circle
includes at least one sensor for each compartment, each sensor being placed at
an angular displacement about the center post-axis identical to that of the angle
defined by any two adjacent door panels 52. In the illustrated revolving door,
adjacent panels meet at 90° so that the sensors are separated by 90°. Although
this geometry is preferred, there are many other configurations and numbers of
sensors which will provide suitable coverage of the housing and which fall within
the spirit and scope of the invention.
In general, operation takes place as follows: Once an authorized
user has been identified by the card reader 110 or 114, main processor 194 activates
position detection system 197 and also activates drive system 60 to revolve the
compartments. At the same time, or substantially contemporaneously, the main processor
194 instructs security controller 294 to activate sensors 99a-99h to detect non-empty
compartments. The sensors emit bursts of ultrasonic waves and detect return echoes
from objects, including people. FIG. 3 shows controller 294 in association with
memory 394 and sensor 99a. Connection with, and operation of, the other sensors
is the same.
In particular, sensor 99a receives, at preset time intervals, a digital
waveform A1 from the controller having a frequency in the ultrasonic
range. The sensor has a transmitter 199a, which includes an amplifier for translating
the electrical waveform into successive bursts of ultrasonic acoustical waves directed
from the sensor head toward the floor of each compartment. Each sensor head also
includes a receiver 299a having a sense amplifier for detecting return echoes of
the waves. The transmitter and receiver are typically dormant when there is no
attempted passage through the revolving door. That is, signal A1 is
not being generated or sent.
During attempted passage, the transmitter and receiver are activated
by controller 294 which sends signal A1, and also a signal GC1,
adjusting the gain of the sense amp to an amount appropriate for receiving the
echoes. Preferably, the gain of the sense amp is increased over time by controlling
the time period between each clock signal in signal GC1. In other words,
the gain clock signal selectively increments the gain of the receiver in digital
steps, which may be set and implemented by using an integrated circuit in the
sensor head. Each pulse on the gain clock line increments a counter in the sense
amp in receiver 299a to select the next highest incremental gain step. The counter
is reset to the first, i.e., lowest gain step, by a burst signal. Control of the
time spacing between gain clock pulses determines the rate of increase of gain
with time following the burst, thus eliminating the need for different sensor heads
for different environments. A suitable gain clock signal is active low and is
approximately 15 microseconds wide.
The amount of increase of gain with respect to time may be selected
and set at installation, based primarily on the door structure. For example, in
a door with highly polished or mirror-like surfaces, a smaller gain with time
is appropriate than in a door with a textured rubber floor and bar-like door wings.
The bursts A1 through A8 are typically relatively
short, e.g., 0.5 ms, and drive the transmitter at a frequency on the order of
48 kHz, but this frequency may vary, as explained below. Preferably, the bursts
are active low.
After each burst, security controller 294 waits a predetermined period
of time so that the sense amp in sensor 99a can receive the echoes of any objects
the burst encounters. This "echo receive time" is at least as long as a maximum
desired distance d set for the sensors to detect objects in the chambers. For
example, in a typical door with a floor-to-ceiling distance of 8', d could be set
to 7' (12" above the floor). The echo receive time is determined empirically,
e.g., when the door is installed, or is calculated based on the speed of the ultrasonic
waves. Preferably, the time between bursts is set greater than the echo receive
time, so that any reverberations will die out, or substantially die out, by the
next burst. In addition, interference from other chambers will be minimized.
The echoes are received by the sense amps in sensors 99a through
99h in real time, and the gain of the sense amps is controlled over this time to
effectively convert the echoes into digital signals B1
The sense amps simply are "go"/"no go" detectors that pass a single-bit digital
signal B1 to an input port of the controller 294.
One of the problems with using sensors in a relatively closed structure,
such as a revolving door, is noise from echo reverberation causing false detection
of objects. The present invention solves this problem in a novel way. The problem
of echo reverberation is shown in FIG. 4A. When the bursts have a constant cycle
rate, "ghost" echoes of an initial echo occur due to multiple reflections, especially
in a closed chamber and especially where the energy waves are sufficiently powerful
to enable detection of small or soft objects. The ghosts will be received at the
same elapsed time following each particular burst. To avoid reading these ghosts
as true echoes, the system is modified in two ways. First, the burst cycle time
is varied, as shown in FIG. 4B. This causes ghosts to be misaligned. The preferred
time between bursts alternates such that T cycle 1 corresponds to 3° of door movement,
T cycle 2 corresponds to 3° plus one-half of the echo receive time, T cycle 3
corresponds to 3°, and so on. Second, the detected echoes following each burst
are stored (in memory 394 shown in detail in FIG. 5 as explained below) in relation
to the elapsed time from the most recent burst, and the stored echoes from (at
least) the last two bursts are logically ANDed to obtain a results array R. Any
echoes that occur at the same time interval after both the last two bursts will
result in a "1". Otherwise, the result is "0" for that time interval. As shown
in FIG. 4A, where the cycle times do not vary, ghosts will occur in cycles 2 and
3 at the same elapsed time, causing an erroneous detection. However, as shown
in FIG. 4B, the ghosts do not occur at the same elapsed time due to the varying
burst cycle, so the ghosts are cancelled out by the ANDing process.
Another problem that can arise by using sensors in a revolving door
is interference caused by echoes or reflections from bursts in one chamber reaching
sensors in other chambers. Often, the door wings are formed solidly, thus preventing
interference. In such a case, burst signals A1 through A8
are sent in any desired fashion, e.g., simultaneously, staggered, or sequentially.
That is, as shown in FIG. 4C, signals A1
through A8 are each
formed by signal portions I, II, etc. However, if the door wings are constructed
non-solidly, interference is likely to occur, so it is preferable to send sequential
or staggered signals A1
through A8. That is, A1
and A2 are sent to sensors 99a, 99b (e.g., in period I), then signals
A3 and A4 are sent to sensors 99c and 99d (e.g., in period
II), followed by signals A5 and A6 being sent to sensors
99e and 99f (e.g., in period III), then signals A7 and A8
are sent to 99g and 99h (e.g., in period IV). This pattern keeps repeating. Sequential
emission avoids detection of echoes due to bursts of sensors in one area by sensors
in another area.
Any reasonable staggered or sequential rotation of sensor operation
is acceptable. The stagger or sequence time should be set, taking into account
the gain of the sensor head and the dimensions of the chambers, as the smaller
the chambers and the greater the gain, the more multiple reverberations will be
likely to interfere with sensors in other chambers. Accordingly, the greater the
delay time between the activation of sensors in one chamber and activation of
sensors in another chamber, the more the reverberations die out. It should be noted
that reduction of the gain too much will jeopardize the ability to detect small
or soft objects, including reducing the ability to detect card passback.
With reference to FIG. 5, the storage of echoes and the ANDing process
will be explained in more detail. The memory is preferably in the form of multiple
storage arrays 101, et seq. Each array has eight columns, each column for storing
echoes of a particular sensor. Each bit in each column corresponds to an amount
of time it takes, following a burst from that particular sensor, for an echo to
return to the sensor. As time corresponds directly to the distance an object is
from the sensor, each bit in a column also corresponds to a particular distance
of an object from the sensor. In the disclosed embodiment, there are sixty-four
bits in each column. If the distance d is 7' (84"), and each bit represents a predetermined
incremental distance such as 1.5", fifty-six bits represent 7'. The controller
294 keeps track (e.g., by a timer, counter, or other means) of how much time has
elapsed since a burst, and places the "echo" or "no echo" signal received from
the sensor in the appropriate bit for that amount of time. That is, the controller
294 will place "1" (echo) or "0" (no echo) in each bit, at least up to fifty-six
in array 101 for echoes of a first burst. Following a second burst, the controller
fills array 102 in the same way. The process continues until array 10n has been
filled. Then, the controller fills the results array R by logically ANDing each
matching pair of bit and sensor numbers from each array 101 through 10n. For example,
the value stored in bit 1 for sensor 1 in array 101 will be ANDed with the values
stored for bit 1 for sensor 1 in arrays 102 through 10n, and the result will be
stored in bit 1 for sensor 1 in the results array R. If all the first bits are
"1", the first bit in the results array will have a "1"; otherwise it will have
a "0". The arrays 101, 102 ..., are preferably filled in a circular pattern.
This logical ANDing process, together with the varying of the burst
repetition rate (cycle time), removes, or at least minimizes, the affect of any
ghost reflections that get stored in any of the arrays 101 through 10n. For example,
if cycle times of the burst signals are constant, the ghost echoes are likely to
be stored in coincident bit numbers in each array 101 through 10n, causing a "1"
to be incorrectly stored in the results array R. When the cycle times are varied,
ghosts are not likely to coincide, so a false "1" stored in a particular bit in
one array will be eliminated during logical ANDing by a "0" in the same bit number
in another array. Generally, two arrays are sufficient to eliminate ghosts, but
if memory space is available, more arrays ensure greater reliability. The filling
of the storage arrays 101 through 10n and the results array R are all preferably
done in real time, but can be delayed, if desired.
Another problem with ultrasonic detectors is that a door panel passing
beneath the sensor returns an echo as would an object or a person in the compartment.
Accordingly, it is necessary to provide security controller 294 with a mechanism
for distinguishing between a door panel echo and an item in the compartment. If
an echo is returned from some minimum distance within which the top of the door
panel lies, the controller interprets the echo as being from a passing door panel
and does not undertake security procedures. In FIG. 5, the minimum distance is
represented by bit number "m" in each array and results array R, which is shown
as the second bit. (In general, the number will depend on the distance from the
sensor to the top of the door panel, and the incremental distance that each bit
in an array column represents.) So, when bits 1 and 2 are "0", no door wing is
passing by. However, if bit 1 and/or 2 is "1", a door wing is assumed to be passing
When a door wing has been detected, the system, i.e., controller
294, blanks out all responses, e.g., ignores any further sensor feedback from the
sensor(s) for which the wing has been detected. So, if a "1" is in bit 1 or 2
for sensors 99c and 99d (e.g., sensors 3 and 4 in FIG. 5) in array 101, the controller
294 clears all bits in array 101 for sensors 99c and 99d. The same will be true
if the controller detects a "1" in bit 1 or 2 in the next array 102. This clearing
process has the effect of creating all "0s" in the results array R for the columns
corresponding to the sensors (99c and 99d) where a door frame has been detected,
due to the ANDing process. If clearing takes place after ANDing, the results array
is either cleared in the corresponding column or ignored for that corresponding
The clearing process is important to avoid erroneous detection of
an object. When a door frame passes under a sensor, there often are numerous reflections
of an ultrasonic burst between the sensor face and the top of the door frame. Such
reflections would cause "1s" to be stored in the column corresponding to the sensor
for several time periods in the memory array, which might correspond to three or
four feet downward into the chamber. Accordingly, it is possible that these, or
some of these, false "ls" will AND with other false "1s" and cause the results
array to falsely indicate detection of an object. Although the count in the door
position detection system 197 could be used to determine when door frames are
passing particular sensors and the results array can be ignored for those sensors,
the "1s" recorded in the array 101, 102, ..., or 10n, might AND with future false
"1s" to create a false object detection. Clearing only the column corresponding
to the sensor detecting a door frame enables random placement of the sensors.
Use of array clearing also eliminates any dependence on tolerances in door position
detection. Moreover, as the door frame passes the radially outer sensors in fewer
burst cycles (and thus fewer degrees of rotation) than the radially inner sensors,
the controller recovers faster from door frame passage at the outer sensors. Thus,
sensing ability can be recouped relatively quickly, and without the tolerance
problems incurred by relying on door position detection.
Controller 294 evaluates the contents of the results array R and
passes the echo or no echo information to main processor 194 for decision making
regarding empty and non-empty compartments. That is, controller 294 preferably
sends at least eight signals (i.e., eight input lines) to processor 194.
The first four signals indicate object detection (other than a door
frame) at sensors 99a or 99b, 99c or 99d, 99e or 99f, and 99g or 99h, respectively.
Alternatively, a signal could be sent for each sensor. The fifth and sixth signals
indicate object detection by trapped man sensors 99i, 99j, respectively. The seventh
and eighth lines issue anti-piggybacking signals for the entrance and exit, as
discussed later. Additional inputs to indicate alarm output, tampering with the
sensor(s), failed sensor(s), or the like, may be added.
Where the control system is equipped with antipassback (prevention
of card passback) features, such as disclosed in U.S. Patent No. 4,627,193, object
detection can be used to improve the reliability of the system. If an object has
not been detected in the authorized chamber by a predetermined amount of rotation
of the door wings, such as 90° from their starting position, the processor could
stop and reverse the drive system until the door wings are returned to their starting
position. For example, with renewed reference to FIG. 2, if the starting position
is with wings 52 lying along lines A and B, and if the ID device 110 indicates
authorized entry at area 26, at least one of sensors 99a, 99b must indicate an
object by the time the door wings have moved 90°. Actually, when security measures
are required, the main processor preferably should begin stopping the door at some
point less than 90°, so that a smooth stop can be made before the compartment
communicates at all with the exit 46.
This antipassback feature can also require at least one of sensors
99c, 99d to indicate an object at some time between when the door wings have moved
90° to when they have moved 180°. Thus, even though antipassback normally prevents
the same ID device from recognizing the same card twice, if the authorized user
neglects to enter the door, the ID device where the user inserted the card will
still recognize that card.
In accordance with another aspect of the invention, the system detects
piggybacking. To do this, the system determines a threshold height, which is a
predetermined percentage of a maximum height detected, and determines the total
time that height readings exceed this threshold. If the total time reaches or
exceeds a predetermined time, the system interprets this as piggybacking. The system
also detects two individuals when height readings exceed the predetermined threshold
height, drop below it, and then exceed it again. This latter test looks for "two
peaks and a valley."
The anti-piggybacking system will be explained in more detail with
reference to FIG. 5A, which shows additional details of memory 394. There is an
additional array which keeps track of the maximum height HMAX detected
by each sensor for each burst. (This number is preferably stored in a binary form,
but is shown in base 10 in FIG. 5A for simplicity.) As bursts occur at, or substantially
at, increments of 3° of rotation of the door, the height is indexed by the door
angular rotation from its starting position of line A in FIG. 2. Thus, for example,
in FIG. 2, the door angle is about 45°. Since the door preferably rotates at a
constant speed, the door angle corresponds to elapsed time from the time that door
The maximum height is determined for each sensor by starting with
the earliest detected echo by that sensor following each burst. This number can
be taken from the array 101, 102, ... or 10n which is currently being filled,
or even from the results array R. For the readings shown in array 101 for sensor
2 in FIG. 5, the earliest detected echo is at bit number 44. Where each bit represents
1.5" and the total chamber height is 8' (96"), the current maximum height is 96"
minus 1.5" x 44 which equals 30". The maximum height is updated for each burst.
Therefore, in the example shown in FIG. 5A, sensor 2 (e.g., sensor 99b) first
detects an object at 9° of rotation. Sensor 1 (e.g., sensor 99a) has not yet detected
an object. The security controller calculates the height as 30" (e.g., a briefcase
at bit 44) and stores this in the memory array indexed at 9°. The maximum height
is then multiplied by a predetermined percentage x, which is sufficiently small
to detect people bending or kneeling, yet not too small as to cause almost anything
to be interpreted as piggybacking. Such a percentage could be on the order of
25%, or even up to about 90%, depending on the device's tolerances and the amount
of security required and whether or not briefcases and the like are to be detected.
Thus, the threshold HTH for sensor 2 at 9° is 30x, which is obviously
exceeded by 30" where x is less than 100%. The memory also keeps track of the
total time tAT above the threshold. This is now 3°, or one occurrence.
At 12°, both sensors 1 and 2 detect the object at 30" above the floor,
so the threshold for both sensors is 30x. Again, 30" is above 30x, so now the time
above the threshold for sensor 1 is 3° and for sensor 2 is 6°. At 15°, sensor
1 still detects only the top of the object, while sensor 2 now is detecting an
individual's head or hat at 72" from the floor. From 18° and on, the maximum height
detected is never more than 72", so the threshold remains at 72x for both sensors
1 and 2.
As noted above, the security controller compares the time above the
threshold to a predetermined time TAT, and if the predetermined time
is met or exceeded, the system interprets this as two individuals. In addition,
even if the predetermined time is not met, the system will interpret dropping below
the threshold, then rising above it again, as two individuals. This situation
is shown in FIG. 5A, where, at door angle 39°, sensor 2 drops to zero, then returns
to 69" at 45°. Sensor 1 also detects two individuals, as it drops to zero at 45°,
then returns to 69" at 48°. Therefore, even if 66° of door rotation is insufficient
to meet the time test for sensor 1, and 54° is insufficient to meet the time test
for sensor 2, the "two peaks and a valley" test will be met.
The total time test need not necessarily be the same for sensors
1 and 2, because the total time an object is under sensor 1 will tend to be greater
than sensor 2 due to the placement of sensor 1 closer to the door's axis. In addition,
the memory arrays in FIG. 5A could be replaced with one memory space or register
for each of "maximum height," "threshold," and "time above threshold," which are
updated after each burst, and also a space to keep track of when there has been
a first peak, a valley, and a second peak.
The total time that the detected height should be at, or above the
threshold to indicate piggybacking is preferably in a broad range between 15° to
80° (5-16 occurrences), and preferably the inner sensor, i.e., sensor 1 is set
at a longer time than the outer sensor, i.e., sensor 2, e.g., by 6° to 12°. The
broad time range depends upon a trade-off between security and incorrect detection
of piggybacking in that the shorter the time, the greater the security, but the
more likely that a single user such as one with a package, or unusually heavy,
or wearing a large hat, will be detected as piggybacking.
With reference to FIG. 6, which is a flowchart of the main operations
of the processor and security controller, an authorized user first inserts a card
into one of the key card readers 110, 114 to begin operation of the door. The
device 110 or 114 determines whether the user is authorized (step 6-1), and if
so, the processor 194 starts the drive system (step 6-2). A variable i is set to
1 (to represent array 101) (step 6-3), and the processor determines whether the
user has passed from the entry point to exit point (step 6-4). If so, the drive
system is deactivated (step 6-5) by the processor 194 and trapped man sensors
99i and 99j (described below) are activated (step 6-18) by the security controller
294. If passage is not complete, the controller sends signals A1 through
A8 to sensors 99a-99h, and the sensors emit ultrasonic energy waves
In steps 6-7 and 6-8, the echoes (signals B1
are received for each sensor and stored in array "i". The ANDing process also takes
place to fill or update the results array (step 6-8). When the results array R
is filled/updated, the security controller evaluates the results array to find
any echoes and their distances (step 6-9). This step may involve performing fail-safe
functions, as discussed in U.S. Patent No. 4,682,153 (Boozer et al), checking the
echoes to determine if a floor echo is present, and the like.
Now that the results array is filled and evaluated, in step 6-10
the security controller 294 determines the maximum height (HMAX), threshold
height (HTH), and time at or above HTH (tAT).
At step 6-1, the controller compares the actual time tAT with the predetermined
time limit TAT. If tAT does not exceed TAT, the
controller also determines if two peaks with a valley in between have been detected
(step 6-12), and if not, the controller then determines whether or not a door
wing has been detected (by examining the first m bit(s) in each column of array
"i") (step 6-13). If a door wing is detected, the clearing operation is performed
(step 6-14). The controller 294 will clear the columns in array "i" which correspond
to any sensors detecting a door wing. If, as shown in FIG. 6, ANDing has already
taken place, the controller may also ignore, e.g., inhibit, output for the corresponding
columns in the results array. Alternatively, ANDing could be delayed until after
the clearing operation.
The controller 294 may also detect sensor failure or blockage (step
6-15), and implement security measures in that case (step 6-20). Such security
measures will also be invoked if tAT ≥ TAT, or if a second
peak is detected after a first peak and a valley, since the controller will issue
a signal (indicating piggybacking) to the controller. Security measures may include
any or all of the following which are appropriate (as in other situations where
security measures are appropriate): stopping further progress of the door, stopping
and reversely rotating the door, and initiating an alarm. If no door wing is detected,
or after clearing (with no failure detection), the processor 194 examines the
inputs from the security controller 294. Whether or not a chamber is authorized
or unauthorized is determined by the processor 194, using outputs from identification
device 110 or 114, such as in U.S. Patent No. 4,627,193, or other suitable means.
That is, authorized entry at area 24 will be relayed by the identification device
114 to the processor 194, which will then recognize signals on the first or second
line from sensor 99a or 99b, or 99c or 99d as authorized, and signals on the third
or fourth line from sensor 99e or 99f, or 99g, or 99h as unauthorized. (The opposite
is true for authorized entry indicated by device 110.) Accordingly, the processor
knows which chambers are authorized and which are unauthorized for use, for steps
6-16 and 6-17. If there are echoes in unauthorized chambers, security measures
are taken. When security measures are taken, the memory is preferably cleared.
The memory is also preferably cleared where security measures have not been taken
by 90° of turn.
In the case where object detection is used to supplement an antipassback
feature, the processor performs step 6-17. That is, the processor checks for echoes
in authorized chambers by using the information on the first line or two lines
to it from the controller indicating detection or no detection at sensors 99a,
99b and 99c, 99d, the inputs of devices 110 and 114, and the input of the position
detection system 197 to determine if echoes have been received in the authorized
chambers by the predetermined amount of time or amount of door rotation. In this
way, the position detection system, which keeps track of the authorized chamber,
serves to keep track of the authorized user. If no echoes are received, then security
measures are implemented (step 6-20).
If there are no echoes in unauthorized areas, and there are echoes
in the authorized areas (or there is no antipassback feature), then the controller
294 next determines which storage array will be updated in response to echoes
from the next burst to be generated. This is done by determining whether the storage
array "i" that has just been filled is the last one (i=n) (step 6-21). If array
"i" is the last one, "i" is set to one (step 6-3) so that the first array 101 has
its contents replaced by the echoes in response to the next burst. If the storage
array that has just been filled is not the last array 10n, then "i" is incremented
by 1 (step 6-22), so that the next array has its contents replaced. Thus, the
contents of each array are successively updated, and the contents of the results
array are updated each time a storage array has been updated.
Sensor failure or blockage may be detected in several ways. If sensors
are all positioned such that all (or some) door wings will align with the sensors
at the same time, the processor or controller can simply check the results array
at the first and second bits for each sensor (or the ones which will align) to
determine if there is a "1" in at least one of the first and second bits for each
sensor. If all the sensors do not show a "1" in at least one of the first two
bits, tampering, malfunction, or other problem could be assumed. Another method
is measuring the amount of time that the first two bits contain at least one "1",
and assuming there is a sensor malfunction, jammed door, or tampering if the predetermined
time for the door to pass the sensor has been exceeded. In such a case, an alarm
is triggered, or building security is notified.
The range "d" to which the echo receive time is set is based on a
compromise between optimum coverage and avoiding noise caused by echoes from the
floor, which can occur due primarily to changes in the velocity of sound with
temperature. That is, as temperature increases, the velocity of sound increases
causing the floor to appear to move upward. The shift in apparent floor position
is about 0.1% per degree Fahrenheit. For a 10' floor-to-ceiling distance, there
is a shift of about 1' per 100°F.
In accordance with a further feature of the invention, the range
is controllable. As shown in FIG. 3, five DIP switches 81 through 85 set the range,
each switch representing an incremental increase in the range. For example, switch
81 is 48", switch 82 is 24", switch 83 is 12", switch 84 is 6", and switch 85
is 3", so that turning on all the switches results in a 93" range. If the ceiling
height is 8' (96"), the recommended maximum range is 7' (84"), as discussed above.
A reasonable minimum range is two-thirds of the door height (i.e., 64"). These
DIP switches are shown connected to the controller 294, but could alternatively
be inputted to the processor 194.
In response to the setting on the DIP switches, the controller determines
how many bits in each column of the arrays to fill (or to pay attention to). For
example, an 84" setting corresponds to 56 bits, and a 72" setting is 48 bits.
The optimal maximum distance setting (set by the DIP switches) can be lengthened
if real time temperature compensation is used. Such compensation is performed
by measuring the floor echo return time (i.e., the apparent distance of the floor)
and correcting for any changes from the expected time/distance. This processing
can be performed in any "dead time," e.g., during the time between bursts (after
the last bit in the array has been filled but before the next burst). Other processing,
such as running software timers and finding any failed sensors, can be performed
in the "dead time" too.
Additional DIP switches may be provided to provide an adjustable
percentage x of the maximum height for the threshold height, an adjustable time
limitation TAT, an adjustable length of time that a valley is detected
between two peaks, and other factors.
As shown in step 6-18, trapped man sensors 99i and 99j operate following
and at times other than authorized passage, in case an item or person is trapped
in a compartment at other than the entrance or exit. These sensors are the same
as the sensors 99a through 99h, and are controlled in the same way as sensors
99a through 99h. A single memory array or multiple memory arrays may be used for
these sensors 99i, 99j, and the ANDing process may also be used. When echoes from
a trapped item or person are detected (step 6-19), security measures (step 6-20)
In a modification, instead of using a separate processor and controller,
the control system can include just one microprocessor/controller to perform all
of these functions, such as represented by the box 494 shown in Figure 3 in broken