Switch actuator

A compact switching apparatus for a model railroad track, the apparatus having the capability of smoothly driving a track switch between terminal positions while providing for intended manual operation while precluding the reverse operation of the apparatus by the track switch. Circuitry includes light emitting diodes to indicate the position of the switch, and can also provide a residual holding current which helps maintain the switch in its intended position.

FIELD OF THE INVENTION
 The invention relates to model railroad switches and more particularly to
 an actuator for a model railroad switch.
 BACKGROUND OF THE INVENTION
 Although a multiplicity of switch actuators, often referred to as switch
 machines, exists, there is a need for a compact, reliable switch actuator.
 One type of known switch actuator uses solenoid coils arranged in a
 push-pull configuration to move a plunger back and forth. The plunger is
 connected to the switch mechanism by a linkage. A number of different
 actuators of this type are available, and all have the advantage of
 allowing a desirable long thin form factor that is well suited for
 placement between closely adjacent lines of track.
 Push-pull solenoid actuators have several disadvantages. They act very
 quickly, which might seem like an advantage, but fail to accurately
 simulate the action of real switches. In addition, they are electrically
 inefficient and require considerable power to operate. If power is applied
 to a solenoid coil of a push-pull solenoid actuator over an extended
 period of time, either accidentally or purposefully, the coil may generate
 a substantial amount of heat, sometimes enough to cause the destruction of
 the actuator.
 Some switching arrangements cause a switch actuator to move a switch to a
 safe position when a train approaches. Arrangements of this type sometimes
 lead to conditions, such as when a train is stalled on a section of track,
 that apply power to actuators for an extended period of time. While
 thermal protection could be added to push-pull solenoid switch actuators,
 doing so would increase the price and complexity of the actuators, large
 numbers of which may be required in complex railroad layouts.
 Another disadvantage of push-pull solenoid actuators is that while the
 actuator can effectively operate the switch mechanism, the reverse is also
 true, that is applying force to the switch mechanism can easily move the
 solenoid, thereby allowing the switch mechanism to be manually moved from
 one position to another. This can create problems. If the switch is
 manually moved from one of two safe positions, derailments can occur.
 Also, some control systems require that the position of all switches is
 known, and the possibility that a switch can be manually moved from the
 position selected by the actuator frustrates this.
 Some push-pull solenoid actuators include latching mechanisms to overcome
 this problem. That is, the switch actuators are designed so that the
 solenoid can move the switch mechanism from one position to the other, but
 force applied to the switch mechanism cannot move the switch from the
 selected position.
 In an attempt to overcome some of these problems, actuators are available
 that use small electric motors to operate the switch mechanism. Electric
 motors can more accurately simulate the action of real switches, and are
 desired by enthusiasts. Actuators are available that purposefully reduce
 the speed of operation well below that which is possible with a solenoid
 to more accurately simulate authentic switching action.
 An example of a slow motion switch actuator is described in U.S. Pat. No.
 4,695,016 to Worack. The actuator uses a small high speed motor coupled to
 a gear train for operating an output pin that is connected to a switch.
 While the mechanism described in the '016 patent provides a realistic
 switching action, it introduces an additional problem. The gearing
 mechanism provides no protection against manual operation of the switch.
 The motors used in switch actuators of the type described in the '016
 patent, for cost reasons, are not as small as would be desirable.
 Depending on the particular design, it can be relatively easy to move a
 switch operated by a motor driven switch actuator manually from one
 position to another, intentionally or otherwise.
 Moreover, known switch actuators such as the actuator shown in the '016
 patent, are larger than is desirable, and cannot be physically mounted
 between adjacent lines of track. One solution is to mount the actuators
 beneath the platform supporting the model railroad layout. While this
 hides the bulky actuator, it makes installation more difficult and is
 undesirable for that reason.
 It is an object of this invention to provide a switch actuator, switch
 machine for a model railroad switch that overcomes all of the problems of
 prior art switch machines mentioned above.
 It is another object of this invention to provide a switch machine that is
 compact and reliable.
 It is another object of this invention to provide a switch machine that has
 a long, thin form factor similar to a push-pull solenoid actuator, but
 which has the aesthetic advantages of a motor driven actuator.
 It is another object of this invention to provide a motor driven actuator
 that effectively resists manual movement of a switch in a way previously
 obtainable only in solenoid actuators.
 In accordance with another aspect of the invention, the face gear includes
 a manual actuator permitting rotation of the face gear for manually moving
 a switch.
 In accordance with another aspect of the invention, the face gear includes
 an indicator actuator for visually indicating the position of a switch.
 In accordance with another aspect of the invention, the switch machine
 provides for a small residual current through the motor, which ensures
 that the machine is maintained in a selected position.
 SUMMARY OF THE INVENTION
 Briefly stated, and in accordance with a presently preferred embodiment of
 the invention, a switch machine comprises a motor having an output shaft
 aligned with a longitudinal axis of the motor, a pinion attached to the
 output shaft of the motor, a face gear engaging the pinion, a cam on the
 face gear, an elongated actuator lever having a primary access aligned
 with the access of the motor, and a cam-following surface on the lever
 engaging the cam, the force exerted by the cam on the cam-following
 surface being substantially perpendicular to the axis of the face gear for
 substantially preventing force exerted on the actuator from turning the
 face gear.
 The motor is a DC motor, which is powered by rectified current from an AC
 source. The direction of the current through the motor, and hence the
 direction of rotation of the shaft, is determined by switching the current
 to pass through either of two oppositely disposed steering diodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring now to the drawings, a model railroad switching apparatus 20 has
 an elongate housing 30, with a body 32 which has a substantially flat top
 portion 34 but is open from below. An underside cover plate, which is
 present in the completed assembly, is not shown. As best shown in FIG. 8,
 the housing 30 is mounted alongside a section of track 50 including a
 track switch 52, which lies within the area enclosed by the dotted line
 and consists of two rails 54. Each rail has a pivotable but otherwise
 fixed end 56 and a movable end 58, the movable ends 58 being connected to
 a common throw bar 60 which can be moved laterally relative to the track
 50 between two functional positions. FIG. 8 shows the switch 52 in a
 position which would guide a train through a turnout curve; in the
 alternative position to that of FIG. 8, the train would follow a straight
 through path.
 Within the body 32 is mounted a DC electric motor 70 with a longitudinal,
 reversibly rotatable, driveshaft 76 whereto is concentrically affixed a
 pinion 78, which engages a face gear or crown gear 80. The face gear 80 is
 disposed so that it in response to the rotation of the pinion 78, it can
 rotate about a generally vertical axis 82.
 As best seen in FIG. 4, the side of the face gear 80 opposite the pinion 78
 has a cam 84 which is fixedly attached thereto and therefore rotates about
 the same axis 82. A cam-post 86 projecting upwardly from the cam 84 is
 parallel to, but spaced apart from, the axis 82. The cam 84 has a
 functional surface 88, which is generally concentric with the face gear
 80. A longitudinal lever 90 has a pivot hole 98 movably engaging a pivot
 post 100, which is attached to the body 32. An end 92 of the lever 90
 protrudes beyond the housing 30 through an opening 40, and is operably
 connected to the throw bar 60 by a coupling 62 which is preferably a
 spring link. The lever 90 has a generally rectangular aperture 94, which
 receives the cam 84 so that the functional surface 88 engages a
 cam-following surface 96. When actuated by the motor 70, the cam 84 can
 cause the lever 90 to be move smoothly between a left terminal position
 and a right terminal position, shown respectively in FIGS. 6 and 7,
 causing a corresponding movement of the track switch 52.
 The apparatus 20 also provides that the track switch 52 can be operated
 manually. The cam-post 86 projects above the top portion 34 through an
 arcuate slot 36 shaped to allow the post to be moved by an operator so
 that the cam 84 cam can be rotated and the track switch 52 actuated
 manually. Simply rotating the cam-post 86 from one side to the other will
 rotate the crown gear 80, which drives the lever 90 and throws the track
 switch 52 to its alternate position. However, it is important to
 distinguish between intended manual operation and unintended movement of
 the track switch 52 in response, say, to vibration of the track caused by
 a nearby train. It is evident especially from FIGS. 6 and 7 that any force
 transmitted from the track switch 52 to the lever 90 would be resisted,
 since a resultant force on the cam would be substantially directed towards
 the axis 72 of the face gear 70, and would therefore have insufficient
 moment about the axis 72 to cause rotation of the face gear 70. Therefore,
 unintended movement of the track switch 52 is precluded.
 In response to a drive current, the driveshaft 76 can rotate in a direction
 determined by the position of a cut-out switch 130 with two selectable
 positions. As the cam 84 causes the lever 90 to complete a transition from
 one terminal position to another, the cut-out switch 130 moves from one of
 its selectable positions to the other. The terminal positions of the lever
 are shown in FIG. 6 and 7. The actuation of the cut-out switch 130 is
 accomplished by two trip-posts 102 mounted on the crown gear 80. Depending
 on the current position of the cut-out switch 130, one or other of the
 trip-posts 102 drives against a tab 104 of a latch 106, shown in FIGS. 3
 and 6, to actuate the cutout switch 130, thereby interrupting the drive
 current. When the trip-post 102 pushes against the tab 104, the latch 106
 rotates about a pivot point 107 and a ramp 108 on the latch, shown in FIG.
 3, causes the cut-out switch to change states thereby removing power to
 the motor 70.
 Thus, in response to the movement of the cut-out switch 130, the rotation
 of the motor 70 ceases. It is emphasized that the trip-posts 102 are
 positioned so that they do not actuate the switch 130 until the transition
 of the lever 90 is effectively complete; otherwise the drive current would
 be prematurely interrupted. The electrical operation of the apparatus 20
 will be described later in further detail.
 It is important to note that on the opposite side of the crown gear from
 the motor pinion contact point there is a support post 38 on the top
 portion 34, shown in FIG. 3, that assures intimate contact between the
 crown gear 80 and the pinion gear 78.
 The structural parts of the apparatus 20 are typically made from plastic.
 In particular, the face gear 80, the cam 84, the cam-post 86 and the
 trip-posts 102 are typically molded together as an integral part.
 The switching apparatus 20 includes a printed circuit board 110. An
 electronic circuit 112 for a first embodiment of the apparatus 20 is
 illustrated in FIG. 1, wherein are shown areas corresponding to the
 apparatus 20, a controller 120 and a source 122 of alternating current
 such as provided on most toy train transformers. A first side 72 of the
 motor 70 is connected the AC source 122, and a second side 74 is connected
 to the cut-out switch 130 at a common terminal 132. The switch is driven
 by the lever 90, which is best shown in FIG. 3. The cut-out switch 130
 selectably closes against a left terminal 134 or a right terminal 136,
 which are respectively connected to a left diode 138 and a right diode
 140. The diodes 138 and 140 connect respectively to a left input terminal
 142 and a right input terminal 144, and is electrically oriented in
 opposite directions relative to the motor 70. Thus, current of opposite
 polarity is supplied to the motor 70 according to which of the diodes 138
 or 140 are actuated.
 The left input terminal 142 can be connected to ground by closing a control
 switch such as a left push button switch 150; if the cut-out switch 130 is
 closed against the left terminal 134, as shown in FIG. 1, this completes
 an electrical circuit which includes the motor 70 and the left diode 138;
 the drive current then flows in a selected direction through the motor 70,
 as determined by the left diode 138. Similarly, when the cut-out switch
 130 is closed against the right terminal 136 and a right push button
 switch 152 is actuated, the drive current flows through the motor 70 in
 the opposite direction as determined by the right diode. The driveshaft 76
 rotates accordingly and drives the face gear 80 and cam 84, the lever 90,
 the coupling 62 and the track switch 52 in the appropriate direction. It
 is evident from FIG. 1 that if the wrong push button switch is operated,
 e.g., the right push button switch 152 is actuated when the cut-out switch
 130 is closed against the left terminal 134, no drive current can flow.
 The push button switches 150 and 152 are preferably constructed so that
 they remain closed just long enough to preclude the drive current from
 being interrupted prematurely.
 As indicated earlier, the trip-posts 102 move the cut-out switch 130 to its
 alternate position when the lever 90 reaches its new terminal position,
 breaking electrical contact at one of the input terminals 142 or 144, then
 immediately creating contact at the opposite input terminal 144 or 142.
 This disconnects the drive current and stops the motor 70 without,
 however, establishing an opposite drive current until the next actuation
 of the appropriate push-button switch 150 or 152.
 Being able to tell the position of the track switch 52 at a distance is
 important to alert the operator to possible problems if the track switch
 52 is not thrown to the proper position. This is sometimes done with flags
 or colored lamps, but these are often not easily seen or are large and
 subject to burnout in the case of lamps. To solve these problems the
 switch apparatus 20 and remote controller 120 are equipped with light
 emitting diodes (LEDs).
 Referring again to FIG. 1, the first embodiment of the switching apparatus
 20 has a green LED 160 and a red LED 162. It is not only desirable to show
 the state of the switch, but in particular to have an indication
 characteristic of whether the switch is thrown for straight through travel
 or for a turnout. Generally, if the green LED is illuminated, the switch
 is understood to be set for straight through or mainline travel.
 Conversely, if the red LED is illuminated the switch is in a turnout
 position. This can also be accomplished in a second embodiment of the
 invention, which has an alternative circuit 114 as shown in FIG. 2. With
 circuits 112 and 114 as configured in the states illustrated in FIGS. 1
 and 2, the green LEDs 160 would be illuminated.
 It should be noted that the LEDs 160 and 162, and current-limiting
 resistors 164 are aligned such that current powering the LEDs will flow
 through the motor 70. However, this residual current is not large enough
 to cause the motor 70 to operate. In the circuit 112 of FIG. 1, the
 residual current opposes the direction of flow of the most recent drive
 current, while in the alternative circuit 114 of FIG. 2, it can be seen
 that the residual and the most recent drive currents have the same
 polarity. If the residual current were large enough to be a concern, the
 alternative circuit 114 would be preferred, and can indeed be used to
 advantage. In a switching apparatus 20 for 00, H0, 0 or S gauge, the
 residual current could typically about 10 ma, or about an order of
 magnitude less than the typical motor drive current of the order of 100
 ma. While insufficient to actually drive the motor 70, this residual
 current nevertheless provides a small holding force by trying to drive the
 motor 70 in the same direction as the most recent drive current. In other
 words, the residual current in the alternative circuit 114 tends to hold
 the track switch 52 closed in the intended position. The magnitude of the
 drive current would be in part determined by the choice of resistors 164.
 If the switch machine were permanently coupled to the track switch 52 as is
 currently the case with some manufactured switches, the green led 160 and
 red led 162 would respectively be wired to correspond to straight through
 and turnout travel, as indicated earlier. Sometimes, however, the switch
 apparatus can optionally be mounted on either side of the track 50, and
 the problem is then assuring that the colors correctly indicate the track
 switch position. This switch apparatus provides sockets 166 on the PCB
 into which the LEDs are plugged, permitting the operator to easily unplug
 the LEDs after the switch apparatus is mounted and to plug them back into
 the printed circuit board to provide the correct color indication. This is
 made easier by providing a "D" shaped hole 42 in the cover that encourages
 a match to a flat on the LED, as shown in FIG. 4.
 In summary, then, the invention has the following advantages. The apparatus
 20 provides a compact, track-level electrical device for smoothly driving
 a model railroad track switch 52 so as to simulate the operation of a real
 track-switch; it further provides for intentional manual operation of the
 track switch 52; it can further provide a residual holding current which
 reinforces the track switch 52 in its intended position; and it precludes
 reverse operation of the apparatus 20 by the track switch 52. The
 apparatus 20 does not rise above the height of its associated track and
 can easily be accommodated within the minimum distance by which adjacent
 lines of track are spaced apart to maintain sufficient clearance between
 passing trains.
 The apparatus 20 has been shown and described in connection with model
 railroad switches, but it will be understood that the invention is not
 limited to this application. It could be used in any application where a
 smooth transition is desired. Whereas preferred forms of the invention
 have been shown and described, it will realized that modifications may be
 made thereto without departing from the scope of the following claims.