Switch actuator

Details Switch actuator Switch actuator

2000-07-07

2001-10-30

Morano, S. Joseph (Department: 3617)

Railway switches and signals

Switches

Reexamination Certificate

active

06308920

ABSTRACT:

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.


REFERENCES:
patent: 4077591 (1978-03-01), Ray
patent: 4355776 (1982-10-01), Rydin
patent: 4695016 (1987-09-01), Worack
patent: 5494242 (1996-02-01), Ludwick et al.
patent: 5752678 (1998-05-01), Riley

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