U.S. patent application number 12/613940 was filed with the patent office on 2011-05-12 for apparatus and method for variable torque braking of escalators and moving walkways.
This patent application is currently assigned to Kone Corporation. Invention is credited to Anthony Boom, Thomas Nurnberg.
Application Number | 20110108386 12/613940 |
Document ID | / |
Family ID | 43970232 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110108386 |
Kind Code |
A1 |
Nurnberg; Thomas ; et
al. |
May 12, 2011 |
APPARATUS AND METHOD FOR VARIABLE TORQUE BRAKING OF ESCALATORS AND
MOVING WALKWAYS
Abstract
A braking apparatus and method for an escalator or moving
walkway are provided. The braking apparatus may include a braking
element, a linearly controllable solenoid assembly, a biasing
mechanism, and a control device. The braking element may be adapted
to engage a brake drum or brake disk on a drive shaft of the
escalator or moving walkway. The linearly controllable solenoid
assembly may include a brake coil and an elongated member. The
elongated member may be moveable linearly along an axis and the
braking element may be coupled to the elongated member. The biasing
mechanism may be arranged to bias the elongated member in a first
direction along the axis to increase a torque applied to the drive
shaft by the braking element. The control device may be configured
to modulate a current to the brake coil based on at least one
measured parameter associated with an operating condition of the
escalator or moving walkway, whereby the elongated member is biased
in a second direction along the axis opposite the first direction
to decrease the torque applied to the drive shaft by the braking
element.
Inventors: |
Nurnberg; Thomas; (Port
Byron, IL) ; Boom; Anthony; (Moline, IL) |
Assignee: |
Kone Corporation
Helsinki
FI
|
Family ID: |
43970232 |
Appl. No.: |
12/613940 |
Filed: |
November 6, 2009 |
Current U.S.
Class: |
198/323 |
Current CPC
Class: |
B66B 29/00 20130101;
H02P 3/16 20130101 |
Class at
Publication: |
198/323 |
International
Class: |
B65G 43/00 20060101
B65G043/00 |
Claims
1. A braking apparatus for an escalator or moving walkway,
comprising: a braking element adapted to engage a brake drum or
brake disk on a drive shaft of the escalator or moving walkway; a
linearly controllable solenoid assembly including a brake coil and
an elongated member, wherein the elongated member is moveable
linearly along an axis, and wherein the braking element is coupled
to the elongated member; a biasing mechanism arranged to bias the
elongated member in a first direction along the axis to increase a
torque applied to the drive shaft by the braking element; and a
control device configured to modulate a current to the brake coil
based on at least one measured parameter associated with an
operating condition of the escalator or moving walkway, whereby the
elongated member is biased in a second direction along the axis
opposite the first direction to decrease the torque applied to the
drive shaft by the braking element.
2. The braking apparatus of claim 1, wherein the braking element
comprises a brake band adapted to extend around the brake drum or
brake disk on the drive shaft, and wherein a first end of the brake
band is adapted to be coupled to a fixed element of the escalator
or moving walkway.
3. The braking apparatus of claim 2, wherein a second end of the
brake band is adapted to be pivotably coupled to the elongated
member.
4. The braking apparatus of claim 2, wherein the brake band is
adapted to wrap approximately 270 degrees around the brake drum or
brake disk.
5. The braking apparatus of claim 1, wherein the axis is adapted to
extend substantially parallel to a tangent of the drive shaft.
6. The braking apparatus of claim 1, wherein the elongated member
comprises: a metal core arranged within the brake coil; a linkage
member coupled at a first end to the metal core; and a rod coupled
to a second end of the linkage member and to the biasing
mechanism.
7. The braking apparatus of claim 1, wherein the biasing mechanism
comprises a compression spring.
8. The braking apparatus of claim 1, wherein the elongated member
defines an intermediate portion adapted to be arranged adjacent to
an outer annular surface of the brake drum or brake disk, the
intermediate portion including an arch adapted to provide
additional clearance for the braking element when released from the
brake drum or brake disk.
9. The braking apparatus of claim 1, wherein the control device
comprises a processor, a current regulator device, and software
which, when executed by the processor, causes the control device to
control a braking profile of the escalator or moving walkway upon
receiving a stop command, the software comprising code segments
executable by the processor for: estimating a load on the escalator
or moving walkway by measuring a speed of the escalator or moving
walkway; and outputting an initial brake coil current corresponding
to a brake torque required to stop the escalator or moving walkway
having the estimated load at a stored programmable deceleration
rate.
10. The braking apparatus of claim 9, wherein the software further
comprises code segments executable by the processor for: estimating
a temperature of the brake coil before outputting the initial brake
coil current, whereby the initial brake coil current output
compensates for resistance variations in the brake coil.
11. The braking apparatus of claim 9, wherein the software further
comprises fuzzy logic software having code segments executable by
the processor for: decreasing the brake coil current when a
measured deceleration rate of the escalator or moving walkway is
less than the stored programmable deceleration rate, whereby the
torque applied by the braking element to the drive shaft is
increased; and increasing the brake coil current when a measured
deceleration rate of the escalator or moving walkway is greater
than the stored programmable deceleration rate, whereby the torque
applied by the braking element to the drive shaft is decreased.
12. The braking apparatus of claim 11, wherein the fuzzy logic
software comprises a symmetrical diminishing algorithm executable
by the processor to prevent the current regulator of the control
device from outputting a brake coil current greater than or equal
to a stored programmable maximum allowable value or less than or
equal to zero.
13. The braking apparatus of claim 11, wherein fuzzy logic software
further comprises code segments executable by the processor for:
measuring the deceleration rate of the escalator or moving walkway;
comparing the measured deceleration rate to the stored programmable
deceleration rate; and comparing the brake coil current output to
the maximum allowable value.
14. The braking apparatus of claim 13, wherein when the measured
deceleration rate is greater than the stored programmable
deceleration rate and the brake coil current output is less than or
equal to half of the maximum allowable value, the control device
increases the brake coil current output by an amount that is the
product of the brake coil current output and a predetermined
percentage greater than one hundred percent.
15. The braking apparatus of claim 13, wherein when the measured
deceleration rate is greater than the stored programmable
deceleration rate and the brake coil current output is greater than
half of the maximum allowable value, the control device increases
the brake coil current output by a predetermined percentage of the
difference between the maximum allowable value and the brake coil
current output.
16. The braking apparatus of claim 13, wherein when the measured
deceleration rate is less than the stored programmable deceleration
rate and the brake coil current output is greater than half of the
maximum allowable value, the control device decreases the brake
coil current output by a predetermined percentage of the difference
between the maximum allowable value and the brake coil current
output.
17. The braking apparatus of claim 13, wherein when the measured
deceleration rate is less than the stored programmable deceleration
rate and the brake coil current output is less than or equal to
half of the maximum allowable value, the control device decreases
the brake coil current output by an amount that is the product of
the brake coil current output and a predetermined percentage less
than one hundred percent.
18. The braking apparatus of claim 9, wherein the control device
further comprises a freewheeling diode flyback circuit coupled to
the brake coil, and wherein the software further comprises code
segments executable by the processor for: temporarily inserting an
additional resistance in the freewheeling diode flyback
circuit.
19. The braking apparatus of claim 1, wherein the control device
comprises a processor, a current regulator, and software which,
when executed by the processor, causes the control device to
control a braking profile of the escalator or moving walkway, the
software comprising code segments executable by the processor for:
modulating the brake coil current during a run mode of the
escalator or moving walkway to compensate for temperature changes
in the brake coil.
20. The braking apparatus of claim 19, wherein the software further
comprises code segments executable by the processor for: reducing
the brake coil current to a predetermined optimum value during a
run mode of the escalator or moving walkway.
21. The braking apparatus of claim 1, wherein the control device is
optionally configured to operate the braking element in a fixed
torque mode or a variable torque mode.
22. A method for controlling a braking profile for an escalator or
moving walkway using a braking apparatus comprising a braking
element arranged to engage a brake drum or brake disk on a drive
shaft of the escalator or moving walkway, and a linearly
controllable solenoid assembly including a brake coil and an
elongated member, wherein the elongated member is moveable linearly
along an axis, and wherein the braking element is coupled to the
elongated member, the method comprising: biasing the elongated
member in a first direction along the axis with a biasing mechanism
to increase a torque applied to the drive shaft by the braking
element; and modulating a current to the brake coil with a control
device based on at least one measured parameter associated with an
operating condition of the escalator or moving walkway, whereby the
elongated member is biased in a second direction along the axis
opposite the first direction to decrease the torque applied to the
drive shaft by the braking element.
23. The method of claim 22, further comprising: estimating a load
on the escalator or moving walkway by measuring a speed of the
escalator or moving walkway with the control device; and outputting
from the control device an initial brake coil current corresponding
to a brake torque required to stop the escalator or moving walkway
having the estimated load at a stored programmable deceleration
rate.
24. The method of claim 22, further comprising: estimating a
temperature of the brake coil with the control device before
outputting the initial brake coil current to compensate for
resistance variations in the brake coil.
25. The method of claim 23, further comprising: measuring a
deceleration rate of the escalator or moving walkway with the
control device; comparing the measured deceleration rate to the
stored programmable deceleration rate with the control device; and
comparing the brake coil current output to a maximum allowable
value with the control device.
26. The method of claim 25, wherein the modulating comprises:
decreasing the brake coil current when the measured deceleration
rate of the escalator or moving walkway is less than the stored
programmable deceleration rate, whereby the torque applied by the
braking element to the drive shaft is increased; and increasing the
brake coil current when the measured deceleration rate of the
escalator or moving walkway is greater than the stored programmable
deceleration rate, whereby the torque applied by the braking
element to the drive shaft is decreased.
27. The method of claim 22, further comprising: executing with the
control device a symmetrical diminishing algorithm configured to
prevent the control device from outputting a brake coil current
greater than or equal to a stored programmable maximum allowable
value or less than or equal to zero.
28. The method of claim 25, wherein the modulating comprises:
increasing the brake coil current output by an amount that is the
product of the brake coil current output and a predetermined
percentage greater than one hundred percent when the measured
deceleration rate is greater than the stored programmable
deceleration rate and the brake coil current output is less than or
equal to half of the maximum allowable value.
29. The method of claim 25, wherein the modulating comprises:
increasing the brake coil current output by a predetermined
percentage of the difference between the maximum allowable value
and the brake coil current output when the measured deceleration
rate is greater than the stored programmable deceleration rate and
the brake coil current output is greater than half of the maximum
allowable value.
30. The method of claim 25, wherein the modulating comprises:
decreasing the brake coil current output by a predetermined
percentage of the difference between the maximum allowable value
and the brake coil current output when the measured deceleration
rate is less than the stored programmable deceleration rate and the
brake coil current output is greater than half of the maximum
allowable value.
31. The method of claim 25, wherein the modulating comprises:
decreasing the brake coil current output by an amount that is the
product of the brake coil current output and a predetermined
percentage less than one hundred percent when the measured
deceleration rate is less than the stored programmable deceleration
rate and the brake coil current output is less than or equal to
half of the maximum allowable value.
32. The method of claim 22, further comprising: temporarily
inserting a resistance in a freewheeling diode flyback circuit of
the control device.
33. The method of claim 22, further comprising: modulating the
brake coil current during the run mode of the escalator or moving
walkway with the control device to compensate for temperature
changes in the brake coil.
34. The method of claim 33, further comprising: reducing the brake
coil current to a predetermined optimum value during the run mode
of the escalator or moving walkway with the control device.
Description
BACKGROUND
[0001] 1. Field of Invention
[0002] The present invention relates generally to controlled
braking mechanisms, and more particularly, to a variable torque
braking apparatus and method for use in conjunction with
escalators, moving walkways, and the like.
[0003] 2. Related Art
[0004] Current braking systems for escalators and moving walkways
(also known as, e.g., power walks or travelators) include, for
example, open control loop braking systems with guided compression
springs. Alternatively or in addition, closed control loop braking
systems with ceramic magnetic brakes have been utilized. Each of
these braking systems, however, present a variety of control
issues.
[0005] For example, open control loop systems with guided
compression springs are bi-stable braking devices. That is, the
brake is released during starting and running and applied with a
constant spring force when the escalator or power walk is stopped.
Due to this bi-stable functionality, the stopping distance and
stopping rates can vary widely depending on escalator loading. For
example, a lightly loaded escalator will stop in less time and over
a shorter distance than a fully loaded escalator.
[0006] To reduce the stopping distance differences between no load
and full load conditions on the escalator, a large flywheel is
often added to the motor to offset the effects of escalator
loading. Even though the large flywheel can provide the inertia to
prevent the escalator from stopping too quickly when the escalator
is lightly loaded, this same inertia is counterproductive when the
escalator is fully loaded. The large flywheel requires that the
brakes provide enough torque to stop the load on the escalator as
well as to stop the large flywheel. Thus, the presence of the
flywheel requires the brakes to be oversized for all
applications.
[0007] Moreover, notwithstanding the addition of a large flywheel,
the difference in stopping distance and rate can still vary between
no load and full load conditions. In many applications, this
difference in stopping distances can still pose a problem if the
customer requires that the stop distance range be narrower than the
open loop brake system can provide. Additionally, in the United
States and Canada, the ASME A17.1 Escalator Safety Code limits
maximum deceleration rates as well as maximum stopping
distances.
[0008] Another problem that can arise with open loop spring applied
braking systems is that the available brake torque may diminish
over time due to brake wear or environmental conditions. As a
result, the stopping rates and distances can become non-code
compliant and/or may not meet customer specifications if the brake
is not readjusted or replaced regularly.
[0009] In an effort to provide consistent stopping, some
manufacturers of escalators and moving walkways have added
inverters (e.g., AC drives) to provide dynamic motor braking. The
addition of inverters, however, can also have disadvantages.
Inverters can be costly and can require extra room in the escalator
truss for mounting. This can be prohibitive on some types of
escalators where there is no extra room in the truss. Also, at
least one of a dynamic resistor or a regeneration unit is required
to dump the generated braking energy. Both items also add cost and
require space for mounting.
[0010] Moreover, it is generally not practical to add closed loop
control to guided compression spring braking systems because the
brake coils on these types of units are bi-stable devices.
Bi-stable devices are designed to be either actuated or not
actuated. Consequently, controlling the brake linearly is not
possible through closed loop control.
[0011] Although ceramic magnetic brakes utilizing closed control
loop braking may solve many of the problems inherent in guided
compression spring open control loop braking systems, they
nevertheless present other issues. For example, while stopping
distances and rates achieved using closed loop controlled magnetic
braking systems may be much more consistent than with open loop
spring applied braking systems, the magnetic brake can tend to be
sluggish. Consequently, the braking system can be relatively slow
to hone in on a specific braking torque required for a given
escalator load. The result is that the stopping rate may either
under shoot or over shoot a set point at the beginning of the stop
sequence, thereby producing a "wavy" stop until the control is able
to hone in on the correct torque.
[0012] Furthermore, since the magnetic null characteristics of
magnetic brakes can vary from brake to brake, it is necessary to
tune the closed loop brake controller for each brake before putting
the brake into service. If the brake controller is not tuned, then
it is possible for the brake to drag slightly over time and/or
provide a stop that is not optimum. Also, the use of a magnetic
brake does not allow the addition of a second brake on the same
motor. As a result, magnetic brakes cannot be used for certain
applications, particularly in Europe where the European escalator
code (EN code) requires the use of compression guided springs as
well as a second brake whenever the rise of the escalator exceeds a
certain height.
SUMMARY
[0013] The invention is directed to a braking apparatus for an
escalator or moving walkway as well as a method for controlling a
braking profile for an escalator or moving walkway.
[0014] In an embodiment of the invention, a braking apparatus is
provided. The braking apparatus may include a braking element, a
linearly controllable solenoid assembly, a biasing mechanism, and a
control device. The braking element may be adapted to engage a
brake drum or brake disk on a drive shaft of the escalator or
moving walkway. The linearly controllable solenoid assembly may
include a brake coil and an elongated member. The elongated member
may be moveable linearly along an axis and the braking element may
be coupled to the elongated member. The biasing mechanism may be
arranged to bias the elongated member in a first direction along
the axis to increase a torque applied to the drive shaft by the
braking element. The control device may be configured to modulate a
current to the brake coil based on at least one measured parameter
associated with an operating condition of the escalator or moving
walkway, whereby the elongated member is biased in a second
direction along the axis opposite the first direction to decrease
the torque applied to the drive shaft by the braking element.
[0015] In another embodiment of the invention, a method for
controlling a braking profile for an escalator or moving walkway
using the braking apparatus is also provided. The method may
include biasing the elongated member in a first direction along the
axis with a biasing mechanism to increase a torque applied to the
drive shaft by the braking element. The method may further include
modulating a current to the brake coil with a control device based
on at least one measured parameter associated with an operating
condition of the escalator or moving walkway, whereby the elongated
member is biased in a second direction along the axis opposite the
first direction to decrease the torque applied to the drive shaft
by the braking element.
[0016] Further features and advantages of the invention, as well as
the structure and operation of various embodiments of the
invention, are described in detail below with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The foregoing and other features and advantages of the
invention will be apparent from the following, more particular
description of some example embodiments of the invention, as
illustrated in the accompanying drawings. Unless otherwise
indicated, the accompanying drawing figures are not to scale.
Several embodiments of the invention will be described with respect
to the following drawings, in which like reference numerals
represent like features throughout the figures, and in which:
[0018] FIG. 1 is a partial schematic side view of a braking
apparatus for an escalator or moving walkway according to an
embodiment of the invention;
[0019] FIG. 2 is a partial perspective view of the braking
apparatus of FIG. 1; and
[0020] FIG. 3 depicts a partial schematic illustration of a control
device of the braking apparatus of FIG. 1, including an exemplary
freewheeling diode flyback circuit according to an embodiment of
the invention.
DETAILED DESCRIPTION
[0021] In describing the example embodiments illustrated in the
drawings, specific terminology is employed for the sake of clarity.
However, the invention is not intended to be limited to the
specific terminology so selected. It is to be understood that each
specific element includes all technical equivalents that operate in
a similar manner to accomplish a similar purpose.
[0022] FIG. 1 is a partial schematic side view of a braking
apparatus 10 for an escalator or moving walkway, according to an
embodiment of the invention. The escalator or moving walkway (not
shown herein in further detail) may comprise any known or
conventional escalator or moving walkway as would be understood by
one of ordinary skill in the art. Escalators are also referred to
as moving staircases. Moving walkways are also referred to as
moving sidewalks (or speedwalks), moving ramps (or speedramps),
autowalks, and travelators and may include, for example, a
plurality of pallets arranged one after the other to form a
substantially even and/or linear track extending substantially
horizontally or somewhat inclined relative to a direction of
motion. FIG. 2 is a partial perspective view of the braking
apparatus of FIG. 1.
[0023] The braking apparatus 10 shown in the embodiment depicted in
FIGS. 1 and 2 includes a braking element 12, a controllable
solenoid assembly including a brake coil 14 and an elongated member
16, a biasing mechanism 18, and an electronic control device 20.
The braking apparatus 10 may be arranged and configured to stop the
escalator or moving walkway at a predetermined deceleration rate
and within a predetermined stop distance regardless of the load on
the escalator or moving walkway when an emergency shutoff sequence
or command is initiated. In this way, passengers on the escalator
or moving walkway may remain safe and comfortable during
deceleration. Such an emergency shutoff sequence may be initiated
manually by the pressing of an emergency shutoff button or switch
(not shown) or automatically via one or more sensors (not shown)
arranged to monitor the operating status of the escalator or moving
walkway. The braking apparatus 10 may stop the escalator or moving
walkway by applying a variable torque to an output mechanism of an
AC drive motor 22, in particular, a drive shaft and/or a brake drum
26 (brake disk) secured to the drive shaft 24, based on a measured
load on the escalator or moving walkway.
[0024] According to the embodiment shown in FIGS. 1 and 2, the
braking element 12 may be, for example, in the form of a brake band
of friction material (e.g., metal, plastic, rubber, leather, cloth,
fiber composite, etc.) arranged concentrically around an outer
annular surface 28 of the brake drum 26. The braking element 12 may
be optionally engageable with at least a portion (e.g.
approximately 270 degrees) of the outer annular surface 28 of the
brake drum 26 to apply a variable or adjustable torque thereto. The
braking element 12 may be secured at a first end 30 to a fixed
point on the escalator or moving walkway, for example, on a housing
of the drive motor 22. A second end 32 of the braking element 12
may be pivotably attached to the elongated member 16 to ensure
consistent clearance of the braking element 12 from the brake drum
26 when released. One or more spacing rollers may be utilized in
combination with a pin to pivotably attach the second end 32 of the
braking element 12 to the elongated member 16.
[0025] The brake coil 14 of the solenoid assembly may be mounted on
a bracket or frame 34 which may be fixedly secured to, for example,
the housing of the drive motor 22 or another stationary portion of
the escalator or moving walkway. The elongated member 16 may
include a metallic core 36 moveably arranged within the windings of
brake coil 14 and coupled at an outer end to an intermediate
portion or linkage member 38. The intermediate linkage member 38
may be arranged adjacent to the outer annular surface 28 the brake
drum 26 and may include an arched or curved portion adapted to
provide additional clearance for the braking element 12 when it is
released from the brake drum 26. The elongated member 16 may also
include another end linkage member or rod 40 coupled to the
intermediate linkage member 38 and to an adjustable plate 42. The
elongated member 16, including metallic core 36, intermediate
linkage member 38, and end linkage member 40, could also be formed
as a single integrally formed member.
[0026] The elongated member 16 is arranged to be linearly moveable
bi-directionally along an axis A as indicated by double-ended arrow
B shown in FIG. 1. The biasing mechanism 18, which may be, for
example, a compression spring, is arranged to bias the elongated
member 16 in a first direction (i.e., to the right in FIG. 1) along
the axis A to increase a torque applied to the drive shaft 24 (via
brake drum 26) by the braking element 12. On the other hand, when a
current is supplied to the brake coil 14, the elongated member 16
is biased in a second direction (i.e., to the left in FIG. 1) along
the axis A to decrease the torque applied to the drive shaft 24
(via brake drum 26) by the braking element 12. That is, as current
to the brake coil 14 is increased, the torque applied to the drive
shaft 24 by the braking element 12 is decreased or removed. In this
way, the elongated member 16 is utilized in tension to provide a
low hysteresis, pull release linkage for optimum variable torque
control. The tension in the elongated member 16 maintains a
straight alignment of action and movement to minimize extraneous
lateral movement and friction in the linkage that can occur with
compression-type release linkages. When the braking apparatus 10 is
mounted on an escalator or moving walkway, the axis A may extend
substantially perpendicular to the drive shaft 24 and substantially
parallel to a tangent of the drive shaft 24.
[0027] As shown in the embodiment depicted in FIGS. 1 and 2, the
rod 40 extends through an opening in a fixed plate 44 and is
attached at a second end to the adjustable plate 42 by, for
example, an adjustable threaded connection. The compression spring
18 acts to bias plate 42 and rod 40 in the first direction along
the line of action defined by axis A to increase the torque applied
to the drive shaft 24 (via brake drum 26) by the braking element
12. This is the default safety position of the braking apparatus 10
when no power is provided to the drive motor 22 and/or to the brake
coil 14. Allowing adjustment of the rod 40 relative to the plate 42
provides the ability to adjust the length and force of the
compressing spring 18 and, thus, the torque applied to the brake
drum 26. One or more brake wear switch indicators 46 may also be
provided proximate the rod 40 and plate 42.
[0028] The electronic control device 20 may be electrically coupled
to or in electronic communication with one or more of the brake
coil 14, the drive motor 22, and the brake wear switch indicators
46 via electrical and/or electronic links 50, 52, and 54,
respectively. The control device 20 may include, for example, but
not limited to, a printed circuit board (PC Board) that may
include, for example, a proportional-integral-derivative controller
(PID) such as a programmable logic controller (PLC) or a digital
controller implemented with a microcontroller unit (MCU) or
processor 100. The control device 20 may also be configured with
software, including fuzzy logic software, for execution by the
processor 100. The control device 20 may also include a current
regulator device 62 such as, for example, a pulse-width modulation
(PWM) device.
[0029] The control device 20 may be configured to modulate a
current supplied to the brake coil 14. As noted above, when the
control device 20 outputs a current to the brake coil 14, the
elongated member 16 is biased linearly in the second direction (to
the left in FIG. 1) along the axis A opposite the first direction
to decrease or remove the torque applied to the drive shaft 24 (via
brake drum 26) by the braking element 12. The amount of current
supplied to the brake coil 14 may be varied or adjusted based on
the output value of the PWM device 62 and/or the status of one or
more of the drive motor 22 and the brake wear switch indicators 46
received by the control device 20 via electrical and/or electronic
links 52 and 54. As a result, the torque applied to the drive shaft
24 can be adjusted to control a braking profile of the escalator or
moving walkway.
[0030] During operation of the escalator or moving walkway, the
control device 20 may provide a current to the brake coil 14
sufficient to ensure that the braking element 12 is open, that is,
to ensure the braking element 12 does not contact or apply any
torque to brake drum 26. The control device 20 may, for example,
output a minimum brake coil current necessary to keep the brake
open while conserving energy. Upon initiation of a stop sequence,
for example, by manually pressing an emergency stop button or
automatic sensing of an run operation error, the control device 20
can execute a stop algorithm to modulate the brake coil current as
needed in a closed loop control to apply a variable torque to the
motor output drive shaft 24 to stop the escalator or moving walkway
at a predetermined deceleration rate and within a predetermined
stop distance regardless of the load on the escalator or moving
walkway.
[0031] After receiving a stop command, the control device 20 may
first estimate a load on the escalator or moving walkway by
measuring an instantaneous speed of the AC drive motor 22, to which
power has been cut. For example, upon initiation of the stop
sequence, the control device 20 may request/receive (via link 52)
RPM data of the motor 22 with respect to a motor droop
characteristic at a specified time after the stop command and,
based on the RPM data, calculate the estimated load on the
escalator or moving walkway. Such calculation may involve utilizing
a RPM-load look-up or correlation table. The control device 20 may
then initially adjust (i.e., reduce) the brake coil current to an
estimated level sufficient to stop the escalator or moving walkway
at a stored programmable deceleration rate based on the estimated
load. By doing so, the initial brake torque output command from the
control device 20 may be very close to an actual brake torque
required to stop the given load at the predetermined deceleration
rate. An advantage of having the initial brake torque being very
close to the actual required brake torque is that time is
thereafter minimized for the control device 20 to find the precise
torque required to stop a given load at the predetermined
deceleration rate. As a result, under-shooting and/or over-shooting
the desired deceleration rate is minimized and a more stable
consistent stop is thereby provided.
[0032] The control device 20 may also, upon receiving the stop
command, estimate a temperature of the brake coil 14. As the brake
coil 14 warms up or cools down, the resistance in the brake coil 14
varies proportionately. If temperature variations in the brake coil
14 are not compensated for, a given PWM output could result in a
different brake coil current providing different brake torque
values at different times and thereby prevent the braking apparatus
10 from providing a consistent deceleration over the normal
operating temperature range of the brake coil. The control device
20 may, for example, compensate for brake coil temperature by
monitoring how much the PWM device duty cycle changes during normal
operation. When a stop command is given, the actual PWM output
value may be subtracted from some known PWM output value for a
given brake coil current. The difference is called the offset. The
offset can be positive or negative and may be added to the
estimated PWM output value for loading. In this way, the control
device 20 may be able to compensate for temperature-related
resistance variations in the brake coil 14 and thereby provide a
consistent deceleration rate over the normal operating temperature
range of the brake coil 14.
[0033] The control device 20 may also include closed loop fuzzy
logic software configured to continuously or intermittently adjust
and/or modulate the brake coil current (and therefore the applied
torque) during the stop sequence to precisely control the braking
deceleration rate of the escalator or moving walkway. The control
device 20 may continuously or intermittently measure the
deceleration rate of the escalator or moving walkway via link 52
and compare the measured value to the predetermined stored
programmable deceleration rate. When the measured deceleration rate
of the escalator or moving walkway is less than the stored
programmable deceleration rate (indicating a heavy load), the
control device 20 may decrease the brake coil current, thus
increasing the torque applied by the braking element 12 to the
drive shaft 24. On the other hand, when the measured deceleration
rate of the escalator or moving walkway is greater than the stored
programmable deceleration rate (indicating a light load), the
control device 20 may increase the brake coil current, thus
decreasing the torque applied by the braking element 12 to the
drive shaft 24. The control device 20 may continue to modulate the
brake coil current accordingly until the escalator or moving
walkway comes to a complete stop.
[0034] The fuzzy logic software of the control device 20 may
include a symmetrical diminishing algorithm with clipping logic
executable by the processor to precisely control the deceleration
rate (braking profile) of the escalator or moving walkway during
the stop sequence and to prevent the control device 20, in
particular the current regulator or PWM device 62, from outputting
a brake current (corresponding to the PWM current output value)
greater than or equal to a stored programmable maximum allowable
value or less than or equal to zero. The fuzzy logic software may
include instructions to monitor the actual PWM current output value
and compare this output value to the stored programmable maximum
allowable value. The control device 20 can then output an adjusted
output value corresponding to a particular brake torque to be
generated.
[0035] When the measured deceleration rate is greater than the
stored programmable deceleration rate (set point) and the current
regulator's actual output value (e.g., a PWM value) is less than or
equal to half of the maximum allowable value, the control device 20
may increase the output value by an amount that is the product of
the actual output value and a predetermined percentage greater than
one hundred percent. For example, if the measured deceleration rate
is greater than 175% of the stored programmable deceleration rate
and the actual output value is less than or equal to 50% of the
maximum allowable value, then the actual output value may be
increased by 130%. If the measured deceleration rate is greater
than 150% (but less than or equal to 175%) of the stored
programmable deceleration rate and the actual output value is less
than or equal to 50% of the maximum allowable value, then the
actual output value may be increased by 118%. If the measured
deceleration rate is greater than 125% (but less than or equal to
150%) of the stored programmable deceleration rate and the actual
output value is less than or equal to 50% of the maximum allowable
value, then the actual output value may be increased by 106%. If
the measured deceleration rate is greater than 110% (but less than
or equal to 125%) of the stored programmable deceleration rate and
the actual output value is less than or equal to 50% of the maximum
allowable value, then the actual output value may be increased by
103%.
[0036] When the measured deceleration rate is greater than the
stored programmable deceleration rate (set point) and the actual
output value is greater than half of the maximum allowable value,
the control device 20 may increase the output value by a
predetermined percentage of the difference between the maximum
allowable value and the actual output value. For example, if the
measured deceleration rate is greater than 175% of the stored
programmable deceleration rate and the actual output value is
greater than 50% of the maximum allowable value, then the output
value may be increased by adding 30% of the difference between the
maximum allowable value and the actual output value. If the
measured deceleration rate is greater than 150% (but less than or
equal to 175%) of the stored programmable deceleration rate and the
actual output value is greater than 50% of the maximum allowable
value, then the output value may be increased by adding 18% of the
difference between the maximum allowable value and the actual
output value. If the measured deceleration rate is greater than
125% (but less than or equal to 150%) of the stored programmable
deceleration rate and the actual output value is greater than 50%
of the maximum allowable value, then the output value may be
increased by adding 6% of the difference between the maximum
allowable value and the actual output value. If the measured
deceleration rate is greater than 110% (but less than or equal to
125%) of the stored programmable deceleration rate and the actual
output value is greater than 50% of the maximum allowable value,
then the brake output value may be increased by adding 3% of the
difference between the maximum allowable value and the actual
output value.
[0037] Thus, if the actual output value is less than 1/2 of the
maximum allowable output, then the change in the current
regulator's output value is the product of some predetermined
percent and the actual output value. Whereas, if the actual output
value is greater than 1/2 of the maximum allowable output then the
change in output value is the sum of the actual output value and a
percent of the difference between the actual output value and the
maximum allowable output. So, the farther away from the maximum
output the greater the output value can be increased. Also, the
closer the actual output value is to the maximum allowable output,
then the smaller the output value can be increased. In this way,
the actual output value can never increase to be equal to or
greater than the maximum allowable output.
[0038] In contrast, when the measured deceleration rate is less
than the stored programmable deceleration rate (set point) and the
actual output value is greater than half of the maximum allowable
value, the control device 20 may decrease the output value by a
predetermined percentage of the difference between the maximum
allowable value and the actual output value. When the measured
deceleration rate is less than the stored programmable deceleration
rate and the actual output value is less than or equal to half of
the maximum allowable value, the control device 20 may decrease the
output value by an amount that is the product of the actual output
value and a predetermined percentage less than one hundred percent.
Thus, the logic for decreasing the brake coil current is similar to
that for increasing the current. The farther away from a zero
output, the greater the actual output value can be decreased. Also,
the closer the actual output value is to a zero output, then the
smaller the output value can be decreased. In this way, the actual
output value can never decrease to be equal to or less than a zero
output.
[0039] As the control device 20 recalculates the current
regulator's output value, it limits the actual output value to the
stored maximum or minimum PWM output value. That is, if the
calculated PWM output value exceeds the maximum possible PWM output
value, then the control device 20 sets the PWM output value to the
maximum PWM output value. Likewise, if the control device 20
calculates a PWM output value of less than the minimum output
value, then the control device 20 sets the PWM output value to the
minimum allowed PWM output value.
[0040] A result of the execution of the fuzzy logic software by the
control device 20 is that the deceleration rate may remain more or
less constant regardless of the load on the escalator or power
walk. This can allow longer periods of time between required brake
adjustments since only the torque required to stop a given load is
applied and can eliminate the need to precisely mathematically
model the entire mechanical system of an escalator or moving
walkway in order to determine the appropriate brake torque for a
given load. Furthermore, the symmetrical diminishing algorithm and
clipping logic may provide a more stable, responsive control
without delay time introduced into the system due to what is known
as Integral Wind Up.
[0041] The control device 20 may also include a freewheeling diode
flyback circuit 60 coupled to the brake coil 14. Freewheeling diode
flyback circuits are known in the art and are commonly used to
avoid damage to circuitry due to flyback effects of inductive
loads. FIG. 3 depicts a schematic illustration of a freewheeling
diode flyback circuit 60 of the control device 20 and coupled to
the brake coil 14 and including a permanent flyback resistor 70 on
the anode side of a high speed flyback diode 72. The
microcontroller unit or processor 100 of the control device 20 may
be configured to temporarily insert an additional flyback resistor
74 in the freewheeling diode flyback circuit 60 to reduce the brake
set time. Inserting the additional resistance 74, which is shorted
out by a switch 80 during operation of the escalator or moving
walkway, can reduce the inductance-to-resistance (L/R) time
constant of the brake coil 14. Reducing the set time of the brake
can reduce coasting time and distance during the time it takes for
the brake to set. That is, reducing the set time of the brake can
reduce the amplitude of any velocity increase during the time it
takes for the brake to set when the escalator is heavily loaded and
can provide for more consistent stop profiles over the entire
loading range of the escalator or moving walkway.
[0042] The additional flyback resistance 74 must be removed after a
short duration of time since it may be of sufficient size to
prevent the brake coil 14 from being controlled by the PWM device
62 of the control device 20. Only the normal flyback resistor 70
must remain in the circuit for control of the brake.
[0043] The control device 20 may also, for example, reduce the
brake coil current to a specified minimum level during a run mode
of the escalator or moving walkway to conserve energy. The brake
coil current can be reduced after the brake opens since it takes
less current to hold the brake open than it does to open the brake.
The control device 20 may, for example, modulate or reduce the
brake coil current during a run mode of the escalator or moving
walkway to an optimum minimum value based on measured temperature
changes in the brake coil 14. For example, as the brake coil 14
warms up or cools down, the resistance in the brake coil 14 may
vary proportionately causing a given brake coil current output of
the control device 20 to provide a different relative position of
the elongated member 16 of the braking apparatus 10. If the brake
coil current drops too low, the brake may set during normal run
operation. On the other hand, if brake coil current is too high,
the brake coil 14 could overheat. Thus, controlling the brake coil
open current while compensating for brake coil temperature allows
the control device 20 to hold the brake coil current steady at an
optimum value over the entire operating temperature range of the
brake coil 14. Reducing the brake coil current while in the run
mode may help reduce energy consumption, reduce brake coil running
temperature, reduces escalator controller power supply
requirements, and/or reduces heat dissipation in the control device
20.
[0044] The control device 20 may be optionally configured to
operate the braking element 12 in a fixed torque mode or a variable
torque mode. Furthermore, the braking apparatus 10 may be a modular
unit configured such that multiple braking apparatuses 10 may be
coupled to one or more control devices 20 and stacked on a single
brake drive shaft 24. Such a modular braking apparatus 10 may be
installed with new escalators or moving walkways and may also allow
retrofitting of existing escalators or moving walkways.
[0045] In general, the braking apparatus 10 may provide a
consistent stopping distance and stopping rate for an escalator or
moving walkway for all escalator loading conditions. No flywheel is
required since the closed loop control device 20 compensates for
escalator loading. Moreover, no inverter, braking resistor, or
regeneration unit is required. Also, no adjustment of the brake
control device is required at installation.
[0046] While various exemplary embodiments of the present invention
have been described above, it should be understood that they have
been presented by way of example only, and not limitation. Thus,
the breadth and scope of the invention should not be limited by the
above-described embodiments, but should instead be defined only in
accordance with the following claims and their equivalents.
* * * * *