Note: Descriptions are shown in the official language in which they were submitted.
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ESCALATOR
BACKGROUND OF THE INVE~TION
Field of the Invention:
The invention relates in general to escalators,
and more specifically to arrangements for stopping an
escalator.
Description of the Prior Art:
Rule 80~ of the ANSI A17.1-1978 Safety Code for
Escalators states that "escalators should be provided with
an electrically released, mechanically applied brake capa-
ble of stopping an up or down traveling escalator with anyload up to brake design load".
The maximum braking effort is required to stop a
fully loaded escalator going down~ and thus the brake is
sized accordingly. For examp:le, the brake torque is selec-
ted to provide some minimum value of deceleration, such as
about 1 ft/sec2, when an escalator with rated load is
stopped while transporting passengers from an upper landing
to a lower landing. Thus, any o-ther condition than a fully
loaded escalator going down will result in a higher rate of
deceleration. The highest rate of deceleration would occur
when a fully loaded escalator is braked -to a stop while
transporting passengers from the lower landing to the upper
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landing. rhis may be about 8 to 10 ft/sec2 for a typica~
escalator with a fixed braking torque.
The prior art has disclosed many different
arrangements which adjust the brakin~ effort, in order ~o
decrease the range between the minimum and maximum rates of
deceleration which may occur, by taking such things as
speed, load and/or travel direction into account. For
example, the braking effort may be adjusted (a) according
to the load, (b) according to speed, such as in response to
an error signal which is responsive to the difference
between the actual speed and the desired speed of the
escalator while braking to a stop, or (c) in response to
travel direction. In general, such controlled braking
arrangements add substantially to the cost of an escalator,
as well as to the maintenance thereof, because of the more
complex mechanical and/or electrical apparatus required.
It would be desirable to provide a new and im-
proved stopping arrangement for an escalator which enables
an escalator to stop wit:hin a predetermined selected range
of deceleration rates, without requiring the speed, load or
travel direction to be sensed.
SUM~I~RY OF T~IE INVFNTION
Briefly, the present invention is a new and im-
proved escalator which has a fail-safe, fixed torque brake,
which will decelerate and stop an escalator within a prede-
termined selected range of deceleration, which range ~ay be
much smaller than prior art escalators equipped with a
fixed torque brake. In accordance with the invention, the
inertia of the escalator is increased, such as by adding a
flywheel to the escalator drive mechanism, with the fly-
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wheel being sized to prevent a ful:Ly loaded esc~llatortraveling in the up direction from stopping too cluickly.
This sets the upper limit to the range of deceleration.
The brake is sized to prevent a fully loaded escalator
going down from exceeding a predetermined stopping distance
This sets the lower limit to the range of deceleration.
Thus, a predetermined clesired range of deceleration is
achieved by adding a flywheel of predetermined size, and
selecting the brake to provide a predetermined braking
torque. The desired range of deceleration is then achievèd
automatically for any load and travel direction~ without
requiring speed, load or travel direction to be sensed.
BRIEF DESCRIPTION OF THE DRAWINGS~
The invention may be better understood, and
further advantages and uses thereof more readily apparent,
when considered in view of the following de-tailed descrip-
tion of exemplary embodiments~ taken with the accompanying
drawings in which:
Figure 1 is an elevational view of an escalator
2n which may be constructed according to the teachi~gs of the
invention;
Figure 2 is a plan view of a drive unit for an
escalator constructed according to the teachings of the
invention; and
Figure 3 is a schematic diagram which illustrates
a control circuit for the escalator of Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, and to Figure 1 in
particular, there is shown an escalator 10 of the type
which may utilize the teachings of the invention. Escala-
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tor lO employs a conveyor l2 Eor transpor~ing passengers,
between a Eirst or lower landing 1~ and a second or upper
landing 16. The conveyor 12 is of the endless type, having
an upper load bearing run 18 on which passengers stand
while being transported between the landings, and a lower
return run 20.
A balustrade 22 is disposed above the conveyor 12
for guiding a continuous, flexible handrail 24. The balus-
trade guides the handrail 24 as it moves about a closed
loop which includes an upper run 26 during which a surface
of a handrail 24 may be grasped by passengers as they are
transported along the conveyor 12, and a lower return run
28. The handrail 24 is guided around the balustrade by
suitable guide means, such as a T-shaped guide member which
is located within the C-shaped cross-section of the hand-
rail 24.
Conveyor 12 includes a plurality of steps 36,
only a few of which are shown in Fig~ 1. The steps are
each clamped to a step axle, and ~hey move in a closed
path, with the conveyor 12 being Ariven in a conventional
manller, such as illustrated :in U.S. Patent 3,414,109, or
the conveyor 12 may be driven by a modular drive arrange-
ment as disclosed in U.S. Patent 3,677,388, both of which
are assigned to the same assignee as the present applica-
tion. For purposes of example, the modular drive arrange-
ment is shown in Fig. 1.
As disclosed in U.S. Patent 3,677,388, the con-
veyor 12 includes an endless belt 30 having first and
second sides, with each side being formed of toothed links
38, interconnected by the step axles to which the steps 36
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are connectecl. The steps 36 are supported by main and
trailer rol]ers l~o and 42, respectively, at opposite sides
of the endless belt 30. The main and trailer rollers ~0
and 42 cooperate with support and guide tracks 46 and 48,
respectively, to guide the steps 36 in the endless path or
loop.
The steps 36 are driven by a modular drive unit
52 which includes sprocket wheels, and a drive chain for
engaging the tooth links 38. The modular drive unit 52
includes a handrail drive pulley 54 on each side of the
-conveyor which drives the handrail unit 56.
Fig. 2 is a plan view of drive unit 52 shown in
Fig. 1, with the drive unit 52 shown in ~ig. 2 being con-
structed according to the teachings of the invention. In
general, drive unit 52 includes a drive motor 60, such as a
three-phase, 60 Hz. induction motor, a gear reducer 62,
drive sprocke-t wheels 64 and 66~ and idler sprocket wheels
68 and 70. The gear reducer 62, which may be a commercial
36.2:1 gear reducer, has an input shaft 72 and an output
shaft 74. The drive motor 60 has a motor shaft 76. The
motor shaft 76 is coupled to the input shaft 72 o~ the gear
reducer 62 by any suitable means, such as via pulleys 78
and 80, and a timing belt 82. A broken belt switch 84
monitors the integrity of belt 82.
The output shaft 74 of gear reducer 62 is con-
nected to the drive sprockets 64 and 66, and each driven
sprocket is coupled with an idler sprocket via a drive
chain 86. As illustrated, the drive chain may have three
strands, with the outer two s-trands engaging teeth on the
sprocket, and with the inner strand engaging the teeth on
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the toothe~l links 38, to drive the endless belt 30 about
its guidecl loop. ~ fai:L-safe friction brake 9~, which is
electrically released and mechan:ically applied, is mounted
on input shaf~ 72 of the gear reducer 62. ~rake 90 rnay be
of any suitable type, such as the caliper brake illustrate~
in the hereinbefore-mentioned U.S. Patent 3,677,388, or the
plate type brake illustrated in Fig. 2. In the plate type,
a first plate member 92 rotates with shaft 72, and a second
plate member 94, which is non-rotatable, is pulled back
away from the rotatable plate 92 electrically, against a
pressure from a spring or permanent magnet. If the elec-
trical power connected to the brake is disconnected, ~he
brake sets due to the pressure from the spring or permanent
magnet, and is thus "fail-safe".
While the fail-safe function and the controlled
braking torque function are preferably provided by a single
brake as described, it is to be unders-tood that these func-
tions may be provided by two separate brakes. For example,
an electrically applied brake may be used to provide the
desired braking torque because of the ease in selecting the
torque, and a separate fail-sa~e brake may be used to brake
the escalator due to power failure.
As will be hereinafter explained, a flywheel 100
is added to the drive unit 52, with the flywheel 100 being
preferably applied to that element of the drive having the
greatest rotational speed. Since the stored energy or
momentum provided by a flywheel increases with the square
of the rotational speed, the size of the flywheel may be
reduced to a minimum by applying it to a r~tational part
having the highest rotational speed. Thus, if there is a
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reduction in the pulley arrangement 78 and 80 between the
drive motor 60 and the reducer 62 J the preferable location
for the flywheel is that illustrated in Fig. 2, i.e., on
the motor shaft 76. If there is no reduction in the pulley
arrangement, i.e., the arrangement is 1:1, the flywheel may
be applied to the input shaft 72 of the reducer 62. Or,
the required inertia may be divided and applied to both the
motor shaft 76 and to the reducer input shaft 72. While
the flywheel 100 i5 indicated as being a separate compon-
ent, the flywheel 100 may be designed as part of thè pulley78, the pulley 80~ or both.
The following relationship applies to the drive
unit 52 and escalator arrangement shown in Figs. 1 and 2:
. (~educer ~atio x Brake Torque) + Pas~enger`~oad
(1) deceleratlon =
Illertla of Escalator
When the escalator is traveling in the upward direction,
the passenger load is positive, making both terms in the
numerator of relationship (1) positive, resulting in a
large value of deceleration. When the escalator is moving
in the downward direction, the passenger load is negative,
but always smaller than the brake torque, in order that the
brake be capable of holding a full load of passengers.
Since the two terms tend to cancel, they result in a re-
duced level of deceleration.
From relationship (1), set forth aboveJ it is
recognized that there are two variables that can be ad-
justed to give a desired deceleration, the brake torque and
inertia. It is further recognized that it is not necessary
to provide the same rate of deceleration for any load in
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either travel direction, as a range of deceleration may be
provided which is entirely acceptable for passenger comfort
For purposes of example, it will be assumed that a desir-
able range is between 1 and 4 ft/sec2. Calculat:ions will
be presented for this range, and also for a range of 1 to 2
ft/sec2 .
Using the range of 1 to 4 ft/sec2 as an example,
the greatest deceleration, 4 ft/sec2 will occur in the full
load up direction, since the brake torque and passenger
load have the same sign when traveling up. The minimum
rate of deceleration, i.e., 1 ft/sec2, will occur at full
load down, with all other loads in either direction result-
ing in a deceleration rate between 1 and ~ ft/sec2.
There are two basic equations, one for full load
up, and one for full load down, and two unknowns, the
inertia and brake torque. Thus, it is possible to deter-
mine the exact sizes of the brake and inertia that will
satisfy the equations. Once calculated, these values
identify the smallest values which may be used and still
provide the predetermined selected range of deceleration.
If larger values of inertia are used, larger values of
braking torque must also be used. The net effect is that
the range of deceleration will be reduced. Thus, if a
smaller desired range than 1 to ~ ft/sec2 is selected, such
as 1 to 2 ft/sec2, the flywheel will have to be larger, and
so will the braking torque.
The inertia of the typical prior art escalator is
too small to provide the required amount of inertia to pre-
vent a fully loaded stairway going up from stopping too
quickly, i.e., higher than the selected upper limit of
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ft/sec2, and it may typically be about ~ to 10 ft/sec2..
Thus, adding a predetermined amo-unt of inertia to the
escalator system is a first s-tep in the present invention.
With inertia added to the system, according to the teach-
ings of the invention, the brake of the typical prior art
escalator will then be too small to prevent a fully loaded
escalator traveling in the down direction from exceeding a
predetermined desired ma~imum stopping dis-tance. Thus,
increasing the size or torque rating of the brake, and the
amount of the increase, are also part of the present inven-
tion. As hereinbefore stated, the brake may be the same
type of on-off, fail-safe friction brake commonly used on
escalators. However~ its torque rating will be higher than
on the typical prior art escalator, typically 50% higher
than the average rating.
Tne required flywheel size may be determined for
a predetermined escalator from the following relationships:
(2) Required Inertia = 2 x Raded Passenger Load
eslre ece eratlon Range
(3) Flywheel Inertia = Required Inertia - Actual Inertia
In relationship (2), the deceleration range is
determined by subtracting the minimum desired deceleration
from the maximum desired deceleration.
The required brake torque is ~etermined for a
predetermined escalator from the following relationship:
(4) Brake Torque =
Rated Load x (Max. Deceleration + Min. Deceleration)
Ratio of Speed Reducer x (Max. Deceleration - Min Deceleration~
Using these relationships, the required flywheel
size and brake size have been calculated for typical 32 and
48 inch wide modular drive escalators, with a 20 foot rise.
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The flywheel and brake sizes have been calculated for a
deceleration range of 1 to 4 Et/sec2, and also for a range
of 1 to 2 ft/sec . The calculated 1ywheel and brake sizes
are illustrated in Table I below.
TABLE I
Escalator Speed Flywheel ~ ft2) Brake
(FPM) Applied to Motor Shaft (ft #)
Dec. Rang~ ~ - ft/sec Dec. Rangi ~ _ ft/sec2
1 to 41 to 2 1 to 4 1 to 2
10 32" Width
10.8 35.2 77 142
120 18.6 62.4 77 142
90/120 42.5 142.0 77 142
48" Width
16.3 53 115 214
120 29 93 115 ` 214
90/120 66 212 115 214
While the escalator brake is a fixed brake, i.e.,
it is not adjustable, the braking torque may not be con-
stant throughout the speed range as an escalator is brakedto a stop. The particular brake torque versus speed rela-
tionship will depend upon the specific brake selected. In
determining the flywheel size in Table I, an average brak-
ing torque is assumed. I the braking torque o the par-
ticular brake selected does not increase`appreciably at the
lower RP~I of the drive motor, the calculated size of the
flywheel may be used without change. However, if a brake
is used which does significantly increase the braking
torque at the lower rpm, the flywheel size will have to be
larger than calculated in order to prevent the maximum
deceleration from being exceeded.
Practical experience has shown that some varia-
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tion in sys~em con~ponents is to be expected. The brake
torque, gearing efficiency, drag, etc., can all contribute
to this variation. Thus, it is preferable to specify a
brake which is about 10% larger than the calculations
indicate, with some acljustment means on the brake to pro-
ide, for example~ a plus zero minus 20% torque range.
Then, by running the escalator unloaded, the exact brake
torque for each escalator may be obtained by adjusting the
brake torque until the desired stopping distance is ob-
lo tained. This adjustment will then guarantee the desireddeceleration range regardless of load or travel direction.
~ ig. 3 is a schematic diagram which illustrates a
control arrangement which may be used. A safety relay SFR
is connected between conductors 102 and 104, which are
connected to a source of electrical potential via a string
of safety contacts, shown generally as safety circuits 106.
The safety circuits may include contacts from the broken
belt switch 84, switches responsive to broken step links
38, skirt safety switches, step up-thrust switches, broken
drive chain switches, under/overspeed switch, maintenance
switches, and the like.
If the safety circuits 106 indicate there is no
malfunction in the system, relay SFR is energized and it
closes a contact SFR-l in the circuit of a control relay
CR. A start pushbutton 108 completes a series circuit
between conductors 102 and 104 which also includes the coil
of the control relay CR, and n.o. contact SFR-l of safety
relay SFR. A seal-in contact CR-l of relay CR and a stop
pushbutton 110 are serially connec-ted across the start
pushbutton 10~.
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The drive motor 60 is connected to a source 112
of electrical poten~ial via a contactor lll~ which includes
an operating coil 116. The operating coil 116 is connected
between conductors 102 and 104 via a normally open contact
CR-2 of the control relay CR.
The brake coil BK of brake 90 is connected be-
tween conductors 102 and 104 via a normally open contact
CR-3 of control relay CR, and the safety circuits 106.
Thus, if the safety circuits are all closed, the safety
relay SFR will be energized and its normally open contact
SFR-l will be closed. Actuation o the start pushbutton
108 will then cause control relay CR to pick up and seal in
via its contact CR-l. Contact CR-2 of the control relay CR
will also close to pick up contactor 114 to energize the
drive motor, and contact CR-3 of the control relay CR will
close to energize the brake coil BK and disengage the
brake.
If the stop pushbutton 110 is depressed, relay CR
will drop and its contacts CR-2 and CR-3 will open to de-
energize the drive motor 60 ancl engage the brake ~0. Thesame result will occur i~ any contact of the safety circuit
106 opens, as relay SFR will drop to open its contact SFR-l
and drop the safety relay CR.
