Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
INTEGRATED LOCKING CONTROL AND STATUS INDICATOR FOR
MANUALLY OPERATED RAILWAY SWITCH STAND
FIELD OF THE INVENTION
This invention relates to a mechanism to provide a definite indication of the
position of
the switch controlled by a switch stand and to secure the stand against
unauthorized
switching, and is particularly applicable for stands used in dark territory.
BACKGROUND OF THE INVENTION
A railroad switch includes moveable switch points (sometimes called blades)
that direct
the wheels onto the appropriate track. The switch points are driven from a
first position,
to direct the train onto one track, to a second position, to direct the train
onto another
track, by a power operated switch machine, or by a manually operated switch
stand.
The points are locked in one position until required to be switched back to
the other
position. Rail terminology commonly refers to the switch point position for
the track
most frequently used as the "normal" position, and the position for the track
less
frequently used as the "reverse" position.
A power operated switch machine is typically used in areas of high rail
traffic or in other
areas where the expense of a centrally controlled signal system can be
justified. The
switch machine monitors whether the switch points have been locked and, if so,
in what
position they are locked, and notifies the signal system of this status. The
signal system
uses this information to regulate approaching trains and to ensure safe
operation given
the status of the switch points.
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At locations where the cost of a power operated switch machine is
uneconomical, a
manual switch stand may be used to control the operation of the switch points.
The
manual switch stand is operated by a railway employee standing adjacent to the
track.
To prevent tampering, most manual switch stands located outside of
classification yards
are locked with a padlock. To operate the switch stand, the employee must
unlock the
padlock, disengage the locking mechanism holding the switch points, and lift
or rotate
the hand throw lever to move the points to the new position. The locking
mechanism
must then be engaged and the employee must visually confirm that the points
are held
in the intended position before allowing a train to pass over the switch.
Before leaving
the switch, the employee must leave the switch points locked in a specified
position,
and reattach and relock the padlock. Safe operation of this type of system is
ensured
only if all employees are familiar with, and follow, a detailed set of rules
in order to
secure the switch stand.
However, a single human error can result in a manual switch stand being left
unattended in an incorrect position. If the switch stand is left unlocked,
vandals may
tamper with the hand throw lever, leaving the switch points in an unexpected
position, or
in a position in which the points are not locked in either of the expected
positions.
Numerous train accidents have been documented as a result of employee failure
to
properly secure a manual switch stand. U.S. Patent No. 5,642,870 to Sargis
describes
a switch stand having a locking device to clamp a throw lever within a cradle,
but no
means to secure that locking device against unauthorized operation.
The simplest way to iock a manually operated switch stand is to immobilize the
throw
lever. A switch stand system including a padlock to secure the hand throw
lever is
shown in U.S. Patent No. 6,164,601 to Scheer and McCord. U.S. Patent No.
383,965 to
Manning shows a spring-biased bolt extending into a recess in a throw lever,
securing
the lever until a key is inserted to retract the bolt. U.S. Patent No.
1,092,259 to Harn
shows an integral key-based lock to secure the throw lever. U.S. Patent No.
379,708 to
Manning shows a lock-case on the throw lever which slides to secure the lever
within a
guide on the switch stand. A series of patents issued to Torpey (U.S. Patent
Nos.
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952,022; 949,098; 900,131; and 868,305) show a locking bolt in a casing
integrated into
the switch stand housing, which engages notches provided in the hub of the
throw lever,
immobilizing the hub and lever until the bolt is raised.
A switch stand may also be secured by locking other parts of the switch stand.
A
system including multiple padlocks to secure various parts of the switch stand
is shown
in U.S. Patent No. 7,267,304 to Scheer. Generally, padlock-based security
systems
rely heavily on the competence and attention of the operator, as discussed
above.
In most situations, if a key is to be used to lock and unlock the switch
stand, it is
preferable that the locking mechanism physically retain the key in the lock
until the
points are confirmed to be fully locked in the normal or reverse position, and
the stand is
secured against further movement. This prevents a switch operator from leaving
a
switch open without also leaving his key behind, and also should prevent a key
from
being lost during switch operation. Further, if a key is left behind, it may
be traced to a
particular operator. U.S. Patent No. 525,678 to Dedel describes a specialized
key that
is retained within a lock once the lock is opened to release the throw lever,
and further
includes a belt worn by the operator, to which the key is attached, rendering
it very
difficult to leave a switch open accidentally.
In addition to properly securing the switch points controlled by a manual
switch stand, it
is important to monitor the position of the switch points and to clearly
communicate that
information to an oncoming train before it passes over the switch. If the
switch point
status can be visually displayed to an oncoming train, this allows the train
to stop for an
incorrectly positioned switch. Status display may be done through a flag-based
system,
such as that shown in U.S. Patent No. 7,267,304 to Scheer, which shows a multi-
coloured flag-based system, wherein the colour of the flag displayed to a
train operator
indicates the position of ihe switch. U.S. Patent No. 2,740,041 to Marcum
describes a
status indicator which uses appropriately colored lights to indicate the
switch position.
U.S. Patent No. 5,470,035 to Sagis shows an electrical switch stand having
lights to
indicate switch position.
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In order to monitor the position of the associated switch points, several
systems have
been used. U.S. Patent No. 5,348,257 to Ocampo shows a detection system
located
near the stock rail, along with a heating element to prevent adverse weather
conditions
from affecting the efficiency of the detector. U.S. Patent No. 2,740,041 to
Marcum
describes a status indicator having electrical contacts located between the
rails in the
switch, which respond to movements of the rod connecting the points to
illuminate
appropriately colored signal lights. U.S. Patent No. 6,427,949 to Hager et a[.
describes
a point detection system based on a linear variabfe differential transformer.
Many other
systems use proximity sensors. For example, U.S. Patent No. 6,149,106 to
McQuistian
describes a point position indicator having proximity sensors located on the
stock rails
at a switch. In U.S. Patent No. 5,806,809 to Danner, proximity sensors are
located near
the switch points, with other proximity sensors being located within the
switch machine
to monitor the position of various lock rods and lock bars. U.S. Patent Nos.
6,186,448
to Wydotis et al., 6,688,559 to Brushwood and 6,296,208 to Franke all
incorporate
proximity sensors near a sleeved point detection bar.
A common monitoring system is a switch circuit controller, such as that shown
in U.S.
Patent No. 5,598,992 to Chew. This type of controller is typically mounted to
the
railroad ties and is connected to the operating rod or to one or more switch
rods. Any
movement of a rod causes a crank arm associated with the controller to rotate,
in turn
rotating a cam shaft, and causing the appropriate electrical contacts to be
made within
the controller housing. However, a switch circuit controller must be regularly
adjusted to
compensate for lost motion between the cams of the cam shaft, the crank arm
and the
operating rod, as well as to ensure that all internal movable contacts are
properly
aligned. This is time-consuming, expensive and can be difficult to do
correctly. U.S.
Patent No. 6,484,974 to Franke discloses a switch machine controller using
Namur
sensors to detect point positions. U.S. Patent No. 6,062,514 to McQuistian
also
discloses a switch circuit controller based on proximity sensors.
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It is therefore an object of the invention to provide a locking mechanism and
a point
position indicator that overcomes the foregoing deficiencies.
In particular, it is an object of the invention to provide a simple means to
secure a switch
stand and to obtain constant indications of the status of the switch stand and
of the
associated switch.
It is a further object of the invention to provide a device which will secure
a switch and
will provide constant indications of the status of the switch, without the
need for ongoing
adjustment of the internal components of the device.
These and other objects of the invention will be appreciated by reference to
the
summary of the invention and to the detailed description of the preferred
embodiment
that follow.
SUMMARY OF THE INVENTION
Generally speaking, the invention employs two main mechanisms: an integrated
locking
system and an arrangement of sensors that can continuously notify an external
monitor
or monitoring device as to the status of the switch points.
The integrated lock system is designed to require the operator to insert a key
before
throwing the switch point lock handle. The lock handle must be physically
disengaged
(unlocked) before the switch points can be moved, but the handle cannot be
disengaged until the key is tumed. Further, once the key is inserted properly
it is
retained within the device and can only be removed once the locking handle has
been
retumed to an engaged (locked) position, presumably after the switch points
have been
moved to the desired position.
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To ensure proper and safe operation of the switch, the locking handle cannot
be
engaged unless the switch points are either in the "normal" position or the
"reverse"
position. The locking handle will not lock (and the key therefore cannot be
removed) if
the switch points are at any position between normal and reverse. The operator
cannot
leave the switch points unlocked in a mid-throw position without leaving the
key behind.
Sensors are used to continuously monitor the location and status of the switch
stand,
whether it is unlocked, locked in the normal position, or locked in the
reverse position.
An external device or monitor receives information obtained from these sensors
and
broadcasts the status of the switch points so that approaching trains can be
handled
accordingly.
The locking control and status indicator prevents human error from
compromising the
safety of manually operated railway switches. It requires employees operating
a switch
stand to leave the stand in a locked state, and it continuously indicates the
status of the
switch stand (unlocked, locked in normal, or locked in reverse) through an
external
notification device to a remote monitor.
In one aspect, the invention comprises a rail switch stand comprising an
elongated
spindle mounted for rotation about a vertical axis, wherein rotation of the
spindle is
adapted to cause actuation of a throw rod; a lever for manually actuating
rotation of the
spindle, the plane of motion of the lever being spatially offset from the
axis; a plate lying
substantially -in a horizontal plane and being coupled to an intermediate
portion of the
spindle for co-axial rotation therewith, the plate comprising at least one
engagement
surface for engaging a locking bar, wherein engagement of the locking bar in
the
engagement surface locks the spindle against rotation; and a lock sensor for
sensing
when the locking bar is engaged in the engagement surface. The engagement
surface
may be a notch in the plate. The locking bar may be vertically elongated and
displaceable into and out of engagement with the engagement surface by lateral
movement, which may be effected by movement of a handle member.
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In a further aspect, the invention comprises an enclosure mounted about an
intermediate portion of the spindle, and the plate is disposed in the
enclosure.
In yet a further aspect, the rail switch stand of the invention may comprise a
second
engagement surface, each of the engagement surfaces corresponding to first and
second positions of the throw rod. The engagement surfaces may be disposed
about
the plate at 90 degrees of angular separation.
In another aspect, the invention comprises a rail switch stand having a switch
position
sensor for sensing a rotational position of the plate, the rotational position
corresponding to the position of the throw rod. In a more particular aspect,
the switch
position sensor may comprise two contacts corresponding to two angularly
displaced
other contacts on the plate.
In yet another aspect, the invention comprises a retractable stop member for
retaining
the locking bar in a first position corresponding to engagement with the
engagement
surface when a key is in a locking state.
In another aspect, the invention comprises a switch stand having retention
means to
retain a key within the switch stand when the key is in a non-locking state.
In a more particular aspect, the invention comprises a rail switch stand
having a second
engagement surface disposed about the plate at 90 degrees of angular
separation from
a first engagement surface; and a switch position sensor for sensing the
rotational
position of the plate, the rotational position corresponding to the position
of the throw
rod; the switch position sensor comprising two contacts corresponding to two
angularly
displaced other contacts on the plate.
In another aspect, the invention comprises an integrated lock control and
status
indication device for a manually operated railway switch stand, comprising a
plate; a
locking member engageable with at least one engagement surface in the plate to
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prevent rotation of the plate; a handle member to control engagement and
disengagement of the locking member with the at least one engagement surface;
a lock
means to maintain the locking member in engagement with the engagement surface
until a matching key has been inserted; and a first sensor to sense the
engagement and
disengagement status of the locking member. In a further aspect, the
engagement
surface corresponds to a rail switch position of normal or reverse, and the
locking
member prevents rotation of the plate only if the rail switch is fully in a
normal or reverse
position. In yet a further aspect, the handle member can move into a locked
position
only when the locking member is engaged with the engagement surface, and the
lock
means may retain the key unless the locking member is engaged in the
engagement
surface.
In another aspect of the invention, the engagement or disengagement status of
the
switch and the switch stand may be communicated to an external notification
device.
In another aspect of the invention, the device may comprise a second sensor to
sense
the position of the plate and to provide an indication of a rail switch
position of normal or
reverse. The indication of a rail switch position may be communicated to an
external
notification device.
In yet another aspect, the invention comprises a manually operated railway
switch stand
comprising a throw handle rotatably connected to a spindle, by which switch
points may
be controlled; an plate through which the spindle passes, such that the plate
and the
spindle rotate in a coordinated manner; a locking member that may engage at
least one
engagement surface in the plate to prevent rotation of the plate and the
spindle; a
handle member to manually control engagement and disengagement of the locking
member with the at least one engagement surface; a lock means that maintains
the
locking member in engagement with the plate until a matching key has been
inserted;
and a first sensor to monitor engagement and disengagement status of the
locking
member. The invention may further comprise a second sensor to monitor the
position
of the plate and to provide an indication of a position of the switch points.
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The engagement or disengagement status and/or the indication of a rail switch
position
may be communicated to an external notification device.
In another aspect, the invention comprises a method of operating a rail switch
stand,
comprising the sequential steps of inserting a key to move a retractable stop
member
out of abutment with a locking member; turning a handle member to disengage
said
locking member from a first engagement surface on a plate; actuating a lever
to rotate a
spindle on which said plate is coaxially mounted, thereby rotating said plate
and
wherein rotation of said spindle causes rotation of a throw rod operatively
connected to
said lever; and sensing when said locking member is disengaged from said first
engagement surface through a first sensor means in operative communication
with said
locking member and thereby determining a status of said switch stand. The
status
sensed may be signaled to an extemai notification device. The method may
include the
further step of sensing a position of said throw rod through a second sensor
means in
operative communication with said plate. The position sensed may also be
signaled to
an external notification device,
In another aspect, the invention comprises a method of securing a rail switch
stand,
comprising the sequential steps of moving a lever operatively connected to a
throw rod
and to an elongated spindle, such that said throw rod is in a reverse or
normal position;
actuating a handle member to engage a locking member with an engagement
surface
on a plate mounted on an intermediate portion of said spindle; sensing that
said locking
member is engaged with said first engagement surface with a sensor means;
applying a
retractable stop member to a lateral portion of said locking member; and
removing a key
from a lock means controlling said retractable stop member. The method may
comprise
the further step of locking said lever in place, when said throw rod is in
said normal or
reverse position. A signal that said locking member is engaged with said first
engagement surface may be sent to an extemal notification device. The method
may
comprise the further step of sensing a position of said throw rod through a
second
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sensor means in operative communication with said plate. The position of said
throw
rod may also be signaled to an externat notification device.
The foregoing was intended as a broad summary only and of only some of the
aspects
of the invention. It was not intended to define the limits or requirements of
the invention.
Other aspects of the invention will be appreciated by reference to the
detailed
description of the preferred embodiment and to the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiment of the invention will be described by reference to
the
drawings in which:-
Fig. 1 is a perspective view of a switch stand incorporating the locking
control and
status indicator of the invention;
Fig. 2 is a top perspective view of the switch stand of Fig. 1, with the top
cover of the
locking control and status indicator of the invention removed; and
Fig. 3 is a sectional view of the locking control and status indicator of the
invention,
taken along line 3-3 of Fig. 2;
Fig. 4 is an enlarged sectional view of the locking control and status
indicator of the
invention, taken along line 4-4 of Fig. 2.
DETAILED DESCRIPTION OF THE INVENTION
Referring to Fig. 1, the switch stand 10 is preferably a manual stand
comprising a base
12 supporting a lever or throw handle 14 which moves between normal and
reverse
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11
positions and may be secured in those positions by foot latches 16. Fig. 1
illustrates the
throw handle 14 having a yoke 17 to interact with the foot latch 16, but it
will be
understood that any throw handle 14 of suitable configuration may be used, and
in
particular that the throw handle 14 need not have any yoke 17, but if a yoke
is present,
it may be of any suitable configuration. In addition, a secondary locking
method, such
as a padlock (not shown) may be used to secure the throw handle 14 to one of
the foot
latches 16, as is known in the art. The actuation of the throw handle 14
causes a
vertical, elongated spindle 18 to rotate, moving the appropriate rods, such as
throw
rods, and throwing the associated switch points (not shown). Rotation of the
spindle 18
also moves the mounted flag or target 22 to an appropriate position to
visually indicate
the position of the switch points.
Switch stand 10 is further fitted with an extended support 24 terminating in
an enclosure
26 designed to house the locking control and status indicating apparatus. As
best
shown in Figs. 2 and 3, the spindle 18 passes through the enclosure 26 and is
fitted
within a plate, such as index plate 28, inside the enclosure 26. The spindle
18 is
preferably fitted within index plate 28 such that rotation of the spindle 18
causes index
plate 28 to rotate in a coordinated, preferably essentially co-axial, manner.
Index plate
28 comprises one or more engagement surfaces, which may be of any appropriate
configuration, such as notches 30, and preferably comprises two notches, one
corresponding to a normal switch position, and the other corresponding to a
reverse
switch position.
A locking member, such as lock bar 32, is positioned to engage the index plate
28, and
may be spring biased to remain engaged with the index plate 28, or to force
the lock bar
32 out of engagement with the index plate 28. When the lock bar 32 engages
either of
two notches 30, the index plate 28 cannot rotate. This also prevents the
spindle 18
from rotating, and therefore prevents the throw handle 14 from being rotated,
preventing
the throw rod from being actuated and the switch points from being thrown.
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Lock bar 32 is moved in and out of engagement with the index plate 28 by
operation of
a handle member, such as lock handle 34 (see Fig. 1), which protrudes from the
enclosure 26. Lock handle 34 (see Fig. 1) is coupled to the lock bar 32 by any
suitable
means, such as a screw or bolt. As an additional safety feature, one or more
shear
bolts 36 may be used to couple the two assemblies. Shear bolt 36 is designed
to fail if
excessive force is applied to the lock handle 34, as might be done In an
attempt to
defeat the locking mechanism of the switch stand 10. Lock handle 34 is
preferably
made readily visible in order to allow an operator to easily determine the
position of the
lock. For example, the lock handle 34 may be somewhat large, or it may be
painted a
highly visible or luminous colour. In addition, the lock handle 34 preferably
has at least
two distinct positions, such as vertical and horizontal, so that an operator
can easily
visually verify whether it is locked or unlocked.
As best seen in Fig. 4, a lock mechanism, such as lock core 38, is preferably
located
near the lock handle 34, and may be operated by a regular mechanical key or an
electronic key (not shown). Lock core 38 is preferably located under an
overhang 40 of
the enclosure 26, or under some other type of protective hood, in order to
protect it from
the elements and from tampering. The lock core 38 preferably retains an
inserted key,
by mechanical or electrical retention, as appropriate, at all times when the
switch stand
is unlocked or when the switch points are in a mid-throw position. The lock
core 38
preferably is in a locked state by default, such as by spring-bias means or
magnetic
means, such that the key can only be inserted or removed when the lock core 38
is
locked. When the lock core 38 is in a locked state, a retractable stop member,
such as
lock core cam 42, abuts the lock bar 32, pressing it into the notch 30 and
preventing it
from moving out of contact with the index plate 28 unless lock core 38 is
opened. This
prevents unauthorized tampering with the switch points, and also prevents an
operator
from accidentally leaving the switch unlocked, unless he also leaves his key
behind.
Enclosure 26 further houses one or more sensors, which sense and provide
information
regarding the status of the switch and switch stand. In the preferred
embodiment, a
lock sensor, which may be a lock bar switch 44 (Fig. 2), is in contact with
the lock bar 32
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via one or more contacts 46, which provides an indication of whether the lock
bar 32 is
engaged or disengaged with the notch 30 in the index plate 28. If the lock bar
32 is not
engaged with one of the notches 30, the contact 46 on the lock bar switch 44
will open,
indicating that the switch is unlocked.
A second sensor, such as directional switch 48 which determines the switch
position, is
also located in the enclosure 26, in order to monitor the position of the
index plate 28 as
it rotates between the normal and reverse positions. The rotational position
of the index
plate 28 corresponds to the position of the railroad switch. Preferably, the
directional
switch 48 comprises at least two contacts 50, 52 (Fig. 3), one of which is
closed only
when the railroad switch is in the normal position and the other of which is
closed only
when the railroad switch is in the reverse position. The pair of contacts
provides two
distinct signals, each of which can be correlated to a specific switch
position. The
contacts 50, 52 may be actuated by any suitable engagement with the index
plate 28,
such as fitting into notches in the circumference of the index plate 28 or by
coming into
contact with teeth or other specifically selected contact areas on the index
plate 28.
The signals produced by each of the lock bar switch 44 and the directional
switch 48 are
preferably provided to a remote monitor by an extemal notification system 54.
The
extemai notification system may be of any type known in the art, including but
not
limited to, fixed wayside signals; analogue radio broadcasts to the crew on an
oncoming
train, which may be triggered by DTMF, or automatically as the train crosses
sensors
along the track; digital radio broadcasts to special devices in an oncoming
train; and
analogue or digital messages to a remote rail traffic control office.
Because of the self-contained nature of the locking control and status
indicator, and the
relatively simple binary nature of the signals received from the lock bar
switch 44 and
the directional switch 48, the invention is simple to operate and maintain. In
particular,
the invention is not subject to serious impact or vibrations from passing
trains or
otherwise during operation, and therefore does not require continuous
adjustment
throughout the lifetime of the device.
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The enclosure 26 can also be designed to accommodate additional equipment to
enhance the functionality of the switch stand 10. For example, a remote
locking
mechanism may be used in addition to the lock core cam 42, to further secure
the lock
bar 32. The remote locking mechanism, which may comprise a second lock bolt or
any
other means to immobilize the lock bar 32, would preferably normally be
engaged,
preventing any manual actuation of the switch stand 10. Upon receiving a
command
from a remote or local source, the remote locking mechanism would disengage
from the
lock bar 32, allowing the switch stand 10 to be operated as described above.
Upon
completion of the switching operation, the remote locking mechanism would
return to its
normal default locked condition.
The enclosure 26 may also be fitted with miniature communication equipment to
allow
two-way communications with the switch stand 10. These communications may take
any suitable form, such as conventional radio frequencies currently used by
railways,
commercial cellular phone systems or private satellite communications.
A Global Positioning System receiver may also be incorporated into the
enclosure 26.
This device would allow the switch stand 10 to distinguish its unique position
in an area
where several similarly fitted switch stands are operating.
Operation
In operation, the switch stand 10 is initially locked and aligned to position
the railway
switch points to allow travel along a selected railroad route, in either the
reverse or
normal direction. An operator would insert his electronic or mechanical key
into the lock
core 38, releasing the lock core cam 42 from its abutment with the lock bar
32, thereby
unlocking the switch stand 10. A mechanical key would likely release the lock
core cam
42 by rotating the key, while an electronic key could be rotated, or may send
a signal to
the lock core cam 42, instructing it to release. At this stage, the lock bar
switch 44 is
. . . ..... ~
CA 02678877 2009-09-16
open, indicating that the switch stand 10 is unlocked. Because the index plate
is still in
contact with one of the contacts 50, 52 in the directional switch 48, the
directional switch
48 will indicate that the switch is in the appropriate position, either
reverse or normal.
The extemal notification system 54 will consider these two readings in
combination and
will indicate that the turnout is unsafe for transit at track speed.
The key is preferably retained by the lock core 38, such as by mechanical,
electrical
magnetic or ay other suitable means, and cannot be removed until the switch
stand 10
is relocked.
The operator actuates the lock handle 34, which in tum frees the lock bar 32
from the
notch 30 in the index plate 28. This allows the index plate 28 to rotate
freely. Upon
pressing the foot latch 16, the operator can move the throw handle 14 from its
current
position to the opposite position, e.g. clockwise, in Fig. 1. The spindle 18
rotates,
moving the switch points and causing the index plate 28 to rotate. As the
index plate 28
rotates, it breaks contact with the contact in the directional switch 48,
causing the
directional switch 48 to indicate that the switch points are out of position,
i.e. not in the
reverse or normal position. The lock bar switch 44 is still open, indicating
that the
switch is unlocked. When these two readings are combined, the extemal
notification
system 54 will indicate that the tumout is unsafe for transit at track speed.
If a secondary locking mechanism, such as a padlock on the foot latch 16, is
used, the
operator would typically unlock and remove the padlock at any point prior to
depressing
the foot latch 16.
As the rotation of the throw handle 14 is completed, it will engage the
opposite foot latch
16, and the index plate 28 will complete its rotation, allowing the notch 30
to engage
with lock bar 32. The index plate 28 will also close the appropriate contact
50 or 52 in
the directional switch 48. The external notification system 54 will therefore
signal that
the switch is in the normal or reverse position, and that the switch is still
unlocked,
rendering the switch unsafe for transit at track speed.
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The operator then returns the lock handle 34 to its original position,
engaging the lock
bar 32 with notch 30. The operator can then rotate his key to the original
insertion
position, if necessary, re-engaging the lock core cam 42 with the lock bar 32,
and
forcing the lock bar 32 to remain within the notch 30. The lock bar 32 then
completes
the circuit with the contacts 46 of the lock bar switch 44, so the lock bar
switch 44 can
indicate that the switch is locked. The extemal not'rfication system 54 can
therefore
signal the remote monitor that the switch is in the normal or reverse position
and that
the switch is locked, so that it is safe for transit. These indications
reassure the
operator and the remote monitor that the switch is in a proper position and is
secure
against tampering or operator negligence.
If a secondary locking mechanism, such as a padlock on the foot latch 16, is
used, the
operator would preferably reattach and lock the padlock on to the foot latch
16 holding
the throw handle 14. The switch is then further secured against tampering.
It wil( be appreciated by those skilled in the art that other variations to
the preferred
embodiment described herein may be practised without departing from the scope
of the
invention, such scope being properly defined by the following claims.
