Note: Descriptions are shown in the official language in which they were submitted.
3 03
~BQ~IMITY ~ TQ~
The invention relates to a proximity detector for
the detection of the presence and position of objects and
people or parts ther~of in the path of moving mechanical
devic~s, su~h as automatic sliding doors, automatic swing
doors or moving vehicles of robots, to, for example,
enable corrective safety action to be taken.
Tha present application has been divided from
Canadian patent application No. 522,201.
It is common practice in the construction of
automatic doorways to include means of ensuring that the
doors cannot close on a peræon causing discomfort or
injury. A numb~r of aontactless sy6tem are known for
detecting the pre3ence of a person in a doorway,
particularly the presence o~ a person in the space which
the door is approaching. British Patent Specifications
711515, 856985, 1108884, and European Patent 0097139 are
but a few which de cribe sy tems of this nature.
All of them involve positioning a proximity detector
on the door establishing conditions whereby a person can
be identified in th~ space or volume which the door is
approaching but being able to ignore walls and other fixed
ob~ects by balance bridge t~chniques or by reducing the
sensitivity when the door i~ close to the fixed object.
While this approach works satisfactorily in many
instances, it is not always reliable in practice and
tends to be prone to false ~iring under changing site
conditions. For example, when very close to fixed objects
the slightest variation in door position may cause a
balance bridge circuit to give a false detection, If the
sensitivity is reduced under these condition~, then
'nulls' often occur where detection is not possible.
This invention provides a means of increasing the
sensitivity and range of detection and maintaining and
often increasing the sensitivity when the sensor is very
close to objects not to be detected, without false firing.
It is preferable with sliding or swing doors to
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provide types of protection aB follows:
1) For a person very close to the leading edge or
side of a closing door detection is necessary over the
full length of the leading ~dge or side o~ the door, this
detection range must be adequate to prevent a person
~hand, ~oot, etc.) belng touched by the door, l.e. to be
greater than the ~topplng distance og the door.
2) For a person approaching a door, detection is
necessary to establish the presence of the person to delay
-~ 10 the door closure.
3) With building sliding doors it is necessary to
e~tablish detection o~ a person approaching a door ~o open
the door.
4) With a swing door it is necessary to establish
separate detection of persons approaching a door from
either side to operate a ætop circuit to prevent the door
from hitting one of the persons.
5) With a swing door it is necessary to establish
detection also outside the path o~ the door opening to
allow timely response.
The lnvention uses as its ~asis a method of, and
apparatus for, controlling th~ range and annular vision of
a detection unit which i8 mounted on or near a moving
object (e.g. door) for the purpose of providing
information as to th2 posi~ion o~ other objects,
stationary or movable, within a specified space or volume.
Two types of detection units are discussed, namely
reflective acoustic (e.g. sonic or ultrasonic) and
electromagnetic.
According to the pr2s~nt invention there is provided
a two conductor transmi~sion ~ystem for transmitting
power and data betw~en two ~tations, the system comprising
a first station linked to a second station by only first
and gecond conductors, the first station including a DC
source for supplying the first and second conductors with
DC power, a synchronisation pulse generator, a first
modulator for modulating the DC power fed to the
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conductors with the synchronisation pulses, a data
torminal connected to said first conductor for receiving
data trans~itted from th~ sQcond tation, and first
inhibiting means respons$vs to the synchronisation pulses
to inhibit the passagQ o~ data to th~ data terminal during
the transmission of 6ynchronisation pulses, the second
station comprising data signal generating means connected
to the first and sacond conductors to receive DC power and
synchronisation signals therefrom, the data signal
generating means being arranged to generate data signals
indicative of a monitored condition, a second modulator
for modulating the DC power flowing along the first
conductor in respons~ to the generated data signals, and
second inhibiting mean~ responsive to the data signals
generated to render thQ data signal generating means
insensitive to the data signals appearing on the first
conductor.
~he invention will now be described, by way of
exampl~, with ref~rsnce to the accompanying d$agrammatic
drawings, in which:
Figure 1 shows a ~ensor or detector unit and an
object with a smooth planar ~.urface;
Figur~ 2 ~hows a sen80r unit with a curved object;
Figure 3 shows a sensor unit and its detection
profile;
Figure 4 shows a sliding door with a detection unit
on the top Or the door;
Figure 5 shows a sliding door with a detection unit
on the bottom Or the door;
Figure 6 shows a sliding door with six detection
units;
Figure 7 shows a plan o~ a swing door with two
detection units;
Figure 8 shows a plan of a swing door with twelve
detection units:
Figure 9 shows a plan of a swing door and various
arrangements of detection units;
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Figure lOA shows a section through a detection unit
along line W-W in F~gure lOB:
Figure lOB shows a front elevation of a detection
unit in a position in which it is mounted on the leading
edge of a sliding door:
Figure lOC shows a plan to Figure lOB;
Figure 11 shows a circuit diagram;
Figure 12 is a circuit diagram of one of the
comparators shown in the diagram of Figure 11:
Figure 13 is a block diagram of the synchronisation
circuit for the sensor or det~ctor unit;
F$gura 14 i~ a diagram o~ a multisensor unit;
Figura 15 is a circuit diagram of a blanking
circuit; and
Figur~ 16 is a pulse diagram for the circuit of
Figure 15.
Referring to Figure 1, a transmitter 1 is sending
out energy in the dir~ction 4. Rec~iver 2 is sensitive to
this energy in the direction 7 and will givs an electric
response thereto. Barrier 3 between the transmitter 1 and
the receiver 2 is impermeable to this energy and restricts
the direct coupling of the en~rgy betwe~n transmitter 1
and receiver 2. In the embodiment shown in Figures 1 to
8, the elements 1, 2 and 3 form a single sensor unit. The
illustrated ob~ect 5 has a reflective surface. It is
assumed that the energy s~gnal in direction 4 obeys laws
similar to the laws governing the reflection of light and
so bounces in direction 6 away form the receiver 2.
Similarly in Figure 2 there will be a return energy
signal from the ob~ect 9 in the directlon 7 towards the
rece~ver 2 if the-point of re~lection lies on a tangent 8
with equal angles of incidencQ and reflection. Using
these principles, a system may be constructed to
d~fferentiate between ~mooth and textured surfaces. In
the case o~ a textured sur~ace which is made up o~ a
multltude o~ curved surfaces ~ome will be in such an
orientation as to cause re~lection of energy in the
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direction 7 towards thQ receiv~r 2.
Referring to Figure 3 the said transmitters or
receivers may be transducers of acoustic or
ele~tromagnetic ~nergy (~or example in the infrared region
of the spectrum). These transducers can be manufactured
in suah a w~y that they exhibit maximum radiant intensity
(transmitters) or maximum sensitivity (receivers) in the
direction of the X axis. The intensity or sensitivity of
the transdua~r3 w~ all of~ in proportion to the angle
of their deviation ~rom the X axis. It follows therefore
that these transducers ~ay be considered to radiate
(transmitters) or receive (recaivers) energy in the form
of a conical pro~ile lo. A textured ob~ect 11 will cause
re~lection o~ many signals in the direction 4 ~rom the
transmitter 1 into the receiver 2 (signals in the
direction 7). The size o~ the receiver signals will be
proportional to:
(1) Sur~ace area Or the ob~ect 11 wlthin the
conical detection area 10.
(2) Reflective constant o~ the surface of the
ob~ect 11 ttexture, colour, reflectivity, etc.).
(3) The total distance ~ravelled by the signals.
(4) The distance of the object 11 from the X axis
in the direction of Y and/or Z axes.
The receiver 2 could be connected to a measuring
device (not shown) which gives a response (detection) only
when a present threshold level i8 exceeded. The threshold
may be such that the ob~ect 11 only gives a response with
the conical profile 10. Within this conical profile,
detection will occur. By arrangement of the attitude of
the transmitter 1, barrier 3 and receiver 2 with respect
to each other and to thQ ob~ects to be detected and
objects to be ignored, it i~ possible to control the space
or volume in which dstection occurs.
Referring to Figure 4, a sensor unit 1-3 is mounted
at the top o~ an automatic sliding door 12. The door 12
slides in the direction S. ~he barrier 3 is between the
Y
\
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transmitter 1 and the rQcoiver 2 and re6tricts the direct
signal path. The axis X i8 tilted away from the vsrtical
so as to produce a det~ction pro~ile 10 which extends from
the door edge 12A into the opening. It is preferable that
no signal may bQ ~mitted from the transmitter 1 in such a
direction as to cause reflection from the edge 5 back
towards the rece~ver 2.
The ~dge 5 is assumed to be a relatively smooth
surface and as ~uch will not return any significant signal
to the receiver 2 ~rom the transmitter 1. The object 9,
situated within the d~tection profile 10, possesses
textured surfaces and offer points some o~ which reflect
signals from the transmittar 1 to the receiver 2 (~igure
2).
As the door 12 moves in the direction S and gets
very close to the edge 5, the ~ignals transmitted ~rom the
transmitter 1 are re~l~cted back and ~orth between the
leading edge 12A of the door 12 an~ the edge 5 thereby
increasing the density Or the transmitted and returned
signals. This has the advantage o~ increasing sensitivity
to small ob~ects (e.g~ f~ngers~ when the door is nearly
closed.
The range along the axis X of the sensor unit has to
be accurately controlled to prevent the floor 5A from
being detectedl and yet allow ~or detection of objects on
the floor (e.g. feet). This application $s therefore
most suitable for acoustic transmitters/receivers using
the relatively slow speed o~ sound. When using acoustic
transducers range can be controlled on a "time till
received" basis. In addition, time slot 'blanks' can be
incorporated in the circuit to ignore signals from
protruding ob~ects, e.g. door knobs and frames. This will
be disclosed in more detail in connection with Figures 15
and 16 described hereinafter~
Figure 5 shows an alternative arrangement with the
sensor unit 1-3 mounted at the bottom of the leading edge
12A of the door 12. The arrangement is othPrwise the same
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as that in Figure 4 and the same principles of detection
apply. Here the range along the X axis is no longer
critical provided that the ceiling 5~ is higher than the
detection height o~ the ob~ect 9. Howevar, the detection
range in the dir~ction S rapidly diminishes towards the
floor 5A.
For more critical applications an arrangement of
sensors may be used. Figure 6 show~ a possible
arrangement o~ four sensor units 21-24 mounted along the
door edge 12A o~ whic~ units 21 and 22 ~ace downwards and
units 23 and 24 face upwards. Each sensor unit comprises
a transmitter, a barrier and a receiver as in the prsvious
ex~mples. The angle o~ detection in the Y and Z axes
(Figure 3) has to be increased to give the same range ~rom
the door edge 12A in th~ direction S as in Figure 5.
~owever, the detection range in the X axis is no longer
critical due to the overlapping of the detection profiles.
Therefore instead of the acoustic units used in the
previous examples other, e.g. infrared or microwave, units
may be used. Other arrangements of units may be used to
provide the required detection profile.
The detection profile still diminishes towards the
floor 5A, so that it i8 still difficult to detect an
object near the floor. This can be easily overcome by
using two additional units 26 and 27. Both these units
are looking forward i.e. with their X axes in the
direction S. The sensor unit 26 positioned at the floor
le~el will detect ob~ect~ at th~ floor level. The sensor
unit 27 may have a pro~ila along its X axis greater than
the sensor unit 26 but within the prorile of the sensor
unit 24, and i8 used solQly to disabl~ the ~ensor unit 26
when the door i8 close to the edge 5 to prevent detection
of the edge.
Figure 7 ~hows the plan view of a sensor unit 1-3
mounted on the ~ide A o~ a swing door 12 near its pivot
point 16. The detection profile in the X axis (Figure 3)
is horizontally across the door opening and tilted away
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~rom the door 12 so as to produce a detection profile lOA
which extends from the door on the side A into the opening
area. It is assumed that a wall 35 (or other barrier
extending perpendicular to the door when in its normally
closed position) has a r~latively smooth surface and will
not reflect a ~ignal from the transmitter 1 to the
receiver 2 when the door i~ open. As the door 12 comes to
close proximity with th~ wall 35, th~ signals transmitted
from the transmitter l are re~lected back and forth
between the door 12 and the wall 35 giving an increased
density of transmission and incre~sed detection
~ensitivity to ~mall ob~ct~. A~ with single sensor unit
arrangements on ~liding doors (Figure 4) the range along
the axis X of the unit has to be accurately controlled.
This application i~ therefor~ most suitable for acoustic
implementation (SeQ for exampl~ Figures 12 and 13).
Signals reflected from thQ door jam 13 may be used to
calibrate the overall time ~lot rangs 17 to allow for
automatic site setting to different door widths and to
provide immunity to atmospheric and environmental changes.
Further, the signal reflected ~rom the door jam 13 may be
used to provide its own tim~ 810t blank 14 thus avoiding
detection of the face of the door jam 13. Further time
810t blanks may be insert~d as requested. A similar
sensor pair 15 may exi t on the other side B of the door
12. This arrangement giva~ detection on both sides of the
door in detection area~ lOA and lOB to allow the door to
be controlled appropriately.
Figure 8 show~ the plan view o~ a sensor unit
arrangement 21-27 mounted along the face of a swing door
12. The X axes o~ the units 21 and 22 face at an angle to
the door away rrO~ ths pivo~ point 16, and the X axes of
the unit8 23 and 24 face at an angle to the door towards
the pivot point 16. The det~ction profile in the Y and Z
axes has to be increased to give ~he same range in the
area A as before ~Pigure 7). More care is needed with the
detection profiles o~ units 23 and 24 to prevent
1~0317~
reflection from the wall 35 as the door ~wings about the
point 16 towards the wall 35. Th~ X axis of the detector
26 faces away from the door 12 along a tangent to the arc
of the door. Th~ unit 27 may face in the same direction
as the unit 26 with its detection profile greater than
that of the unit 26 but within that of the unit 24. The
signal from the uni~ 26 serve~ to compensate for the
diminished range of d~tection o* the unit 24 near the
leading edge 12A of the door 12. The uni~ 27 disables the
lo unit ~6 when the door 12 1~ close to the wall 35 to
prevent detection thereof. ~ore or less units may be
needed in the arrangement to provide the required
detection profile. A similar sensor unit arrangement may
exist on the other side B o~ the door 12 to give detection
on both sides of the door.
The principle related are extendable to
transmitters and receivers which are situated not next to
each other but on dir~erent moving or statlonary surfaces.
As long as the transmitter 8ignals have no direct line of
sight to the receiver and the trans~itter signals cannot
bounce off fixed or moving ob~ects which are not to be
detected, e.g. doors, wall or roof, into the receiver to
produce sufficient ~ignal to swamp signals bounced off
ob~ects to be detected, then the transmitters and
receivers and barriers can bQ positioned anywhere.
Figure g shows but a few possible arrangements. In
one of them the tran~mitter 1 i5 mounted remotely from the
receiver 2. The barriers 3A and 3B at the receiver 2
define a conical detection profile while the barriers 3C
and 3D at the transmitter 1 define a conical transmission
profile. The inter~ection of these two conical profiles
defines a d~tection spac~ 10 within which detection of
reflective ob;ects will occur. As is apparent from Fig.
9, there i8 no dirsct line of sight between the
transmitter 1 and receiver 2. ~t will be understood that
by suitable screening or focusing the transmitt~d and
detected energy can acquire any desired profile and
1303~77
11
thereby the shape of the detection space or volume
produced by their intersQc~lon can be defined at will. It
will ~e further und~rstood that the stlle or walls 35A and
35B can be used for said screening. Ob;ect 9, anywhere
within the detection space 10 w~ll cause reflection of the
signals from the transmitter 1 into the receiver 2. As
the door 12 opens in the direction S into the detection
space 10 it will it~elf cause a moving shutter effect by
virtue of its impermeability to the energy used, leaving
a desirable (albei~ r~ducad) detection spacs or volume
extending at all times from the region of the leading edge
12A of the door 12. In prior art designs this has been
the most desirable yet most difficult area in which to
provide detection.
Any other transmittcr-receiver-~arrier combinations
may be arrang~d u~ing thi~ deslgn to cover any space, e.g.
transmitter 4 in combination with r~ceiver 6 to cover a
space nearer the closed door, and/or transmitter 1 with
receiver 7 covering th~ whol~ region between the door 12
and wall or stile 35A, and/or transmitter 8 with receiver
11 to cover the region of the leading edge 12A on the
other side o~ the door wh~n the door is open.
Figures 10A, 10B and 10C show a method of shuttering
an in~rared sensor unit (transmitter 1 and receiver 2) on
the leading edge of the 81~ ding door 12 o~ an elevator car
to give the desired detection profile (space) in the Y and
Z axes. The shuttering i8 achieved by the barriers 3, 4
and 6. The barrier 6 is a channel which restricts the 2
axis profile, the barrier 4 restricts the Y axis profile
to prevent forward vision in the direction S, and the
barrier 3 restricts the direct coupling of signals
between the transmitter 1 and the receiver 2. The
shuttering unirormly modifie~ the det~ction profile of the
units so that tolerances (the variation between optical
and mechanical axis Or the units which gives the inherent
profile of individual transmitters and the receivers
within the units) are no longer critical.
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12
The sensor unit is tilted away ~rom the leading edge
o~ the door 12 by an angle P to give the direction deslred
for the X axis (see Fig. 4). The sensor unit may al~o be
tilted at an angle Q to give the desired direction o~ the
X axis away from the lift car towards the landing.
If the wall being approached has a diffused or
textured surface, it may be desirable to colour it with a
matt-black finish to prevent nuisance detection. The
inside o~ the channel 6 i 8 preferably matt-black to
prevent internal reflectlons corrupting the desired
profile. This is alse de~irable for a pair o~ centre-
opening doors in which the detector~, mounted on the
leading edges of both doors, co~e face to face.
The outside lip 7 of the channel 6 i~ angled and
made reflective. Thus, when the door is very close to the
surface being approached, reflections will bounce back and
forth between the lip8 7 and that surface, thereby
increasing the density of transmis~ion and therefore the
sen~itivlty to æ~all ob~ects (~.q. finger6) i8 further
increased.
Figure 11 shows a circuit which may be used with
infrared detectors shown in Figure 6. Known circuit
techniques can be used to implement it. Each of the
sensor units 21 to ~7 i8 conne¢t~d to its own non-linear
amplifier 8 to 13 through a respective rectifier and
smoothing filter 48 to 53. outputs of amplifiers 8 to ll
are connected to a ~umming amplifier 14, the output of
which ig connected to ons input of each of four
comparators 16 to 19. ~h~ other input of each comparator
16-19 is conneated to one output of the respective one of
the amplifiers 8 to 11. ~ha outputs of the amplifiers 12
and 13 are conne¢ted to two separate inputs of the
comparator 20. The output of all the comparator~ 16 to 20
are connected to th~ input~ of ~h~ logical ''ORIl gate 41.
The output signal 42 from thQ gate 41 i~ the detection
signal indicativQ of ths presQncQ of a detected object.
In the sensor uni~ 21, 22, 23, 24, 26 and 27 the
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13
six infrared transmitter~ may be time-division multiplexed
or modulated at the di~erent ~requencies 80 that the six
rQceivers havQ means to distinguish their respective
transmitter signals. Each receiver signal may be
amplified using its own non-linear amplifier 8 to 13 with
roll off in gain with increasing signal. This technique
increases the dynamic rangQ of the circuit and will
prevent saturation of the amplifier when strong signals
are being received but maintains the sensitivity to
detected objects substantially constant.
The output signal of the summing amplifier 14
represents the average level of the four input signals
from the amplifiers 8 to 11. ~hi~ average signal is used
as the reference level for one input to each of the
comparator~ 16 to 19. The other inputs to the comparators
are derived from the output ~ignals from the amplifiers 8
to 11. The respective comparators givs an output if their
received ~ignal goe~ above or below a threshold band
established from and contred on the reference level from
amplifier 14. The comparator outputs are processed in the
OR gate 41 to give a detection output signal 42. Figure
12 ~hows the comparator 16 in more detail.
The comparator 16 comprises a pair of zener diodes
60 and 61 connected in serie~ with respective resistors 62
and 63 to de~ine the desired threshold band. A pair of
comparator units 64 and 65 each have one input connected
to receive a æignal from amplirier 8. The other input of
the comparator unit 64 i8 connected to the junction
between the resistor 62 and thQ zener diode 60 and the
other input o~ the comparator unit 65 is connected to the
~unction between the zener diode 61 and the resistor 63.
The output of the summing ampli~ier 14 is connected to the
~unction between the two zener diodes 60 and 61. The
outputs of the comparative units 65 and 64 are connected
in common to a respective input of the OR gate 41.
If a small rerlecting ob~ect increases the signal
received by the receiver Or the un~t 21 by a specified
~303177
amount above that received by the remaining receivers, it
wlll be detected as a signal from ampli~ier 8 above the
upper limit o~ the threshold band and the comparator 16
will give an output. Conversely, i~ a large reflecting
ob~ect increases th~ signal by a speci~ied amount to
receivers of the un~t~ 22, 23 and 24, the comparator 16
will still give an output 81 gnal as the signal ~rom the
amplirier 8 is now below the lower limit of the threshold
band established from the now the increased average signal
from the amplifier 14. In other words, any contrasting
surfaces are detected.
In practice the wall b~ing approached may not be a
perfect re~lector and will cause small signals to be
received on receivers o~ the units 21 to 24 when the door
i8 very close. The circuit Or Figure 11 however will not
give an output 42 as all signal~ from the ampli~iers 8 to
11 lncrease equally and therefore the signal output from
amplifier 14 correspondingly increases.
The average signal rrO~ the ampllfier 14 may be used
manually or automatically to reset the outputs of
amplifiers 8 to 11 to eguality at will and during initial
setting. This average signal from the amplifier 14 may
also be used during operation to adjust the outputs from
the amplifiers 8 to 11 i~ there i8 a large, or rapidly
increasing error signal or a continuous comparator signal
output from the comparators 16 to 19.
Detector units 26 and 27 form the floor circuit
(Figure 6).
Unit 26 i8 at th~ floor and unit 27 in the main
detection area. The galn from th~ amplifier 12 receiving
signals fro~ th~ unit 26 is 1GS8 than the gain from the
amplifier 13 rec~iving ignal~ from the unit 27. If the
~ignal from amplifier 12 ~xc0eds tha signal from the
amplifier 13, then ths comparator 20 gives a detection
signal. This ~ 8 fQd to the OR gate 41 to give an output
signal 42.
In an arrangement using acoustic sensors, in order
J
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to avoid the sensors detecting fixed ob~ects such as the
floor or a door knob, th~ blanking circuit shown in Figure
15 can be used. As shown in tha puls2 diagram o~ Figure
16 and under steady stat~ conditions, the transmitter 1
transmits a pulse signal A wh~ch is then reflected by the
door knob a~d the floor to provide pulses Bl and B3 in the
received signal B. Ths6Q signals if sustained will be
mamorised by a reference unit 98, which will then generate
blanking pulses Cl and C3 in ~ynchronism therewith. The
outputs of the referenc~ unit 98 and the receiver 2 are
fed to respactive inputs o~ an AND gate 99. In operation
tha pulses B1 and B3 rec~ived by ths receiver will
coincidQ wlth th~ blanking pu1~03 Cl and C3 and 80 no
output D will occur from th~ AND gate 99.
When an ob~ect to be dQtQcted i8 sensed by the
receiver 2, a pulse B2 will b3 generated. Because this is
a transient pul~e, it will n~t have b~sn stored in the
memory of the reference circuit 98. As a consequence no
corresponding blanking pul8e will have been generated and
so an output D2 will appear at the output of the A~ID gate
99 .
In this way stat~onary ob~ects re~lecting energy to
the receiver will generally be automatically ignored and
only transient objects will b~ detected.
With unmodulated infrared units it is preferable to
synchronise transmission to tha mains supply ~requency to
eliminate potential problems with modulated lighting
(e.g. fluorescent or incande~cent lights) and periodic
mains switching (.e.g. rrOm triac controllers nearby).
The synchronisation ~hould ~e per~ormed outside ~he zero
voltage crossing point, a~ triaca e~c., o~ten switch close
to zero voltage. If this feature is required, the
synchronisation ~ignal deriYed ~rom the mains supply naeds
to be made available at the unit on the moving door.
Further a two wire power path and a single wire return
detection signal path are required rOr the unit. Other
Xnown types of sensor units (e.g. capacitive) may also
1303177
16
require di~erent control slgnal~ at the sensor units.
Prior art systems send these signals 6eparately via a
multicore cable which is susceptible to fatigue and
breakage. It is preferable to use a minimum of conductors
in the flexible cable leading to the moving door to
all~viate this problem and to reduce the speci~ication and
cost. A two-wire system may be used according to the
invention to supply the unit.
The synchronisatlon oircuit ~or transmitting power
and data is shown more clearly in Figure 13. As shown an
AC supply unit 71 supplies AC power to an AC to DC
converter 72 to provide a DC source. A resistor 73 and
the emitter/collector path of a transistor 74 are
connected in series across the output o~ the converter 82.
First and second conductors in the form of flexible wires
or cables 75A and 75B connec~ the emitter/collector path
of transistor 74 in parallel ~ith the emitter/collector
path for a tran istor 76 (mounted on the movable door) and
also feed the sensor unit 79 with power through a
rectifier and filter provided by a diode 77 and a
capacitor 78.
A ~odulator formed by a pulse generator 69 connected
to the AC supply 71 supplies pulse3 synchronous with the
mains frequency to the base of ths transistor 74.
The output from the sensor unit 79 feeds the base of
the transistor 76 and also one input of an exclusive OR
gate 80. The other input of the exclusive OR gate 80 is
connected to the wir~ 75A.
The wire 75A i~ al80 connacted to one input of
another exclusive OR gate 70 forming an inhibiting means.
The outer input of tho gate 70 i8 connected to the output
of the pulse genera~or 69. ~he output of the exclusive OR
gate 70 ~B connected to a remote data terminal device 76,
for example, for a door controller, and/or to provide
further synchronisat$on s~gnals and control signals e.g.
$or further units.
In operation the pul~e~ generated by tho pulse
~303~77
17
genQratOr 69 modulate the power supply fed via line~ 75A
and 75B to the sensor 79 mounted on the movable door.
Sensor 79 iB a data signal generatin~ means and generates
data signals of the monitored condition. It al~o acts as
a sQcond modulator to modulate the signal on the lines 75A
and 75B. The exclusiv~ OR gate 80 acts as a second
inhibiting means to thG sen60r 79 in6ensitive to the
modulation which th~ ssnsor 7g itself produces on the
lines 75A and 75B. The Qxclusive OR gate 70 inhibits the
passage of pulses generated by the pulse generator 69 to
thQ remote device 76.
In this way only a two wir~ link i8 reguired between
a first and second station ~the door and the door frame)
thus reducing the problems of ~atigue.
In addition to the unit~ shown in Figure 6 at least
one further unit may be provided on the edge 5 such that
there is a direct sight between thi~ unit and one of the
units o the door. In this way a 'curtain' deteotion beam
extending acros~ th~ door opening oan be produced, which,
when broken, can be arranged to give a detection signal.
Further the 'curtain' signal may be used to desensitise
unit~ as necessary under adverse operat$ng conditions by
suitable ~odi~ication o~ tha arrangement of the units
relative to each other.
It will be understood that several sensor units can
be combined into an assembly which will then be used as
described in connection with a single unit.
Figure 14 shows a mul~i-element single sensor unit.
As shown four sensors 90 to 93 are positioned on the
leading edge 12A o~ a door so that the proriles overlap ~o
such an extent that the combined prorile 97 has an
extremity which extends generally parallel to the edge
12A. In this way any variation in range of the individual
profiles provided by the individual sensors will only have
a reduced e~fect on the width of the combined profile.
The transmitters of ~our sensors 90 to 93 are fed by
common line 94 and the receivers are connected to
1303177
~8
respectivQ inputs of a ~umming amplifier 95.
It will be appr~ciatQd that this multi-element
sensor unit can replace th~ slngle sensors Or any Or the
embodiments hereinbe~ore described.
With the embodiments described it will be readily
apparent that the manner in which the sensors can be
ad~usted to cover any shape Or detection space renders the
system extremely flexible.
Also while the b~ams p~oduced by individual sensors
are normally divergent to provide volumetric sensitivity
they can instead be made convergent to provide point
sensitivity.
The shape of the transmission and reception profiles
of each sensor can be controlled in many different ways
for example by collimated or divergent lenses, by
reflectors (~.g. parabolic) or by electromagnetic means.
~urthermore instead of beams of energy each sensor
may transmit or rece~ve beams o~ other media for example
air ~ets.
In a modification the barrier 3 between the
transmitter 1 and rece~Yer 2 can be omitted where a
directional property i8 inherent in their construction or
the control circuits are able to ignore a direct as
opposed to a reflected signal.
Experiments with a detQctor according to the
invention wera made in ~hich ob~ects w~re successfully
detected up to a distance o~ 3 ~tres from the censor
units.
