Electricity: motive power systems – Motor-reversing – Automatic and/or with time-delay means
Reexamination Certificate
2000-01-24
2001-10-09
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Motor-reversing
Automatic and/or with time-delay means
C318S282000
Reexamination Certificate
active
06300734
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to motor control apparatus and, more particularly, to a motor control apparatus for a railway switch machine having a reversible motor.
2. Background Information
In order to optionally switch a railroad train operating on a first track to a second, merging track, it is typical to provide a switch with a pair of “switch points” which are selectively movable horizontally to deflect the train toward one or the other of the tracks. The switch can encompass a pair of switch rail lengths of the second track which extend several feet in length with the switch points being essentially tapered end sections of those rail lengths. The switch points, typically labeled as “normal” and “reverse”, are selectively movable back and forth between a pair of stock rails. These provide a normal position in which the train is directed toward the first track by the normal switch point being positioned against a first rail of the first track, and a reverse position in which the train is directed toward the second track by the reverse switch point being positioned against the opposite rail of the first track.
The switch points are typically attached to each other via a plurality of tie rods, at least one of which doubles as a switch throw rod. The throw rod is driven by a remotely controlled electrical switch machine, or, in some instances, by a hand lever operated switch machine, between extended and retracted positions. Depending upon the side of the track on which the switch machine is placed, the extended position can be the normal or the reverse condition of the switch points, and vice versa for the retracted position.
Switch machines employ reversible electric motors to drive a series of gears which are attached to the throw rod. Depending upon the control signals received at the switch machine, the motor is driven one direction or the other to either extend or retract the throw rod and, thus, move the switch points between normal and reverse switching positions. Lock connecting rods are also attached to the switch points. The lock connecting rods passively move back and forth with the switch points and cooperate with locking elements in the machine housing to lock the switch into a normal or a reverse switch position.
Referring to
FIG. 1
, a switch point adjuster
2
is schematically depicted. The exemplary switch point adjuster
2
utilizes two separate rods
3
,
4
and a frog
5
, although a single operating rod (not shown) may be employed. The exemplary switch point adjuster
2
is located at the center of the track
6
, although other such adjusters may be employed on the left side (with respect to
FIG. 1
) and opposite the switch machine
8
. The first rod
3
connects the switch point adjuster
2
to the frog
5
, and the second rod
4
connects the switch point adjuster
2
to the operating bar
10
of the switch machine
8
. Thus, when the switch machine
8
throws six inches, the slack is taken up in the switch point adjuster
2
so that the frog
5
is only moved its required amount. Both operating rods
3
,
4
are supported by support rollers (not shown).
As shown in
FIG. 2
, a railroad switch includes a pair of switch points
12
,
14
which are linked by one or more tie rods
16
. The switch points
12
,
14
are selectively movable between a “normal” position (as shown) and a “reverse” position. In the illustrated normal position, the switch point
12
, commonly called the normal switch point, is positioned against a stationary stock left rail
18
, and the switch point
14
, commonly called a reverse switch point, is moved away from a stationary stock right rail
20
. The stock left and right rails
18
and
20
are anchored to a plurality of cross ties
22
via rail anchors
24
in a conventional manner. In a normal position, the normal switch point
12
directs a train entering the railroad switch straight through the intersection via the right stock rail
20
and the switch point
12
, which tapers outward into a straight left rail
26
past the switch.
In a reverse position (not shown) both the normal switch point
12
and the reverse switch point
14
are moved to the right (with respect to
FIG. 2
) with the normal switch point
12
, thus, moving away from the stock left rail
18
and the reverse switch point
14
moving to a position against the stock right rail
20
. The reverse switch point
14
is then in a position to direct the train to the left via the left rail
18
, which curves to the left past the switch, and via the reverse switch point
14
, which tapers outward to a curved right track
28
past the switch.
The switch points
12
and
14
are selectively moved via a switch machine
30
. The switch machine
30
includes a reversible electric motor (M)
31
(shown in hidden line drawing) in a motor housing
32
. The motor
31
is connected to drive a series of gears
33
,
34
,
35
(shown in hidden line drawing) which, in turn, drive a throw bar
36
(shown in hidden line drawing), either to the left or the right (with respect to FIG.
2
). The throw bar
36
is connected to a throw rod
38
via a linkage
40
. The throw rod
38
, in turn, is connected to the tie rod
16
via a switch basket
41
. The switch basket
41
is internally threaded to receive threads
42
on the throw rod
38
, in order that the switch point position at either end of travel of the throw rod
38
is adjustable. For example, a typical stroke length for the throw bar
36
would be approximately five inches.
Historically, switch machine motor controls employed mostly 3-wire (
FIG. 4
) or 5-wire (
FIG. 5
) control for permanent magnet or wound field motors, respectively.
In a switch machine, linear motion of the mechanism moving the points (such as
12
and
14
of
FIG. 2
) is converted into rotary motion. Rotary operated cam switches, in turn, are used to open the motor circuit at the end of the stroke and steer current to change direction.
FIG. 3
illustrates the operation of cam switch (CSw1)
44
and cam switch (CSw2)
46
. For normal operation, CSw1 is closed for most of the cycle and, then, opens at the end of the cycle to open the motor circuit and stop the motor. For reverse operation, CSw2 is closed for most of the cycle and, then, opens at the end of the cycle to open the motor circuit and stop the motor.
FIG. 4
illustrates how the two cam switches
44
,
46
, in conjunction with a three-pole switch (SW1)
48
, are used to control a three-wire permanent magnet motor (M)
50
using 3 wires
52
,
54
,
56
. In
FIG. 4
, the full normal rotation is shown completed, there is no normal (N) current, CSw1 is open and CSw2 is closed. When SW1 is moved from the normal (N) to the reverse (R) position, reverse (R) motor current flows as indicated and the cam revolves in a suitable rotational direction until CSw2 opens and the motor
50
stops.
FIG. 5
shows how two cam switches
58
,
60
, in conjunction with a double-pole switch (SW2)
62
, are used to control a wound field motor (M)
64
using 5 wires
66
,
68
,
70
,
72
,
74
. In this case, motor armature current is reversed for each of the normal (N) and reverse (R) directions, but current through the field
76
is unidirectional. Operation of the cam switches
58
,
60
is the same as the respective cam switches
46
,
44
of FIG.
4
.
For both
FIGS. 4 and 5
, the point at which the respective motors
50
,
64
stop is not well controlled. This is because the circuit is simply opened and the precise stopping point is determined by inertia and by friction that is to be overcome. The friction is not well controlled, particularly, because the switch machine must operate over a wide temperature range. It is common for the friction to be significantly greater in cold weather because grease at cold temperatures is more viscous.
U.S. Pat. No. 5,747,954 discloses a two-terminal configuration having contacts at the terminals of the motor. An electronic controller circuit for the power down function of a highway crossing guard mechanism eliminates the “pumping” condition
Bozio Robert P.
Franke Raymond C.
Wydotis Leonard M.
Duda Rina I.
Eckert Seamans Cherin & Mellott , LLC
Houser Kirk D.
Nappi Robert E.
Union Switch & Signal Inc.
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